2009-12-02 Jb Evain <jbevain@novell.com>

[mcs.git] / class / corlib / Mono.Globalization.Unicode / SimpleCollator.cs

//
// SimpleCollator.cs : the core collator implementation
//
// Author:
//      Atsushi Enomoto  <atsushi@ximian.com>
//
// Copyright (C) 2005 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

//
// Here's a summary for supporting contractions, expansions and diacritical 
// remappings.
//
// Diacritical mapping is a simple tailoring rule that "remaps" diacritical
// weight value from one to another. For now it applies to all range of
// characters, but at some stage we might need to limit the remapping ranges.
//
// A Contraction consists of a string (actually char[]) and a sortkey entry
// (i.e. byte[]). It indicates that a sequence of characters is interpreted
// as a single character that has the mapped sortkey value. There is no
// character which goes across "special rules". When the collator encountered
// such a sequence of characters, it just returns the sortkey value without
// further replacement.
//
// Since it is still likely to happen that a contraction sequence matches
// other character than the identical sequence (depending on CompareOptions
// and of course, defined sortkey value itself), comparison cannot be done
// at source char[] level.
//
// In IndexOf(), the first character in the target string or the target char
// itself is turned into sortkey bytes. If the character has a contraction and
// that is sortkey map, then it is used instead. If the contraction exists and
// that is replacement map, then the first character of the replacement string
// is searched instead. IndexOf() always searches only for the top character,
// and if it returned negative value, then it returns -1. Otherwise, it then
// tries IsPrefix() from that location. If it returns true, then it returns
// the index.
//
// LAMESPEC: IndexOf() is lame as a whole API. It never matches in the middle
// of expansion and there is no proper way to return such indexes within
// a single int return value.
//
// For example, try below in .NET:
//      IndexOf("\u00E6", "a")
//      IndexOf("\u00E6", "e")
//


using System;
using System.Collections;
using System.Globalization;

using Uni = Mono.Globalization.Unicode.MSCompatUnicodeTable;
using UUtil = Mono.Globalization.Unicode.MSCompatUnicodeTableUtil;
using COpt = System.Globalization.CompareOptions;

namespace Mono.Globalization.Unicode
{
        internal class SimpleCollator
        {
                // this environment variable is for debugging quick check.
#pragma warning disable 169, 414
                static bool QuickCheckDisabled =
                        Environment.internalGetEnvironmentVariable (
                        "MONO_COLLATION_QUICK_CHECK_DISABLED") == "yes";
#pragma warning restore 169, 414                

                unsafe internal struct Context
                {
                        public Context (CompareOptions opt, byte* alwaysMatchFlags, byte* neverMatchFlags, byte* buffer1, byte* buffer2, byte* prev1, bool quickCheckPossible)
                        {
                                Option = opt;
                                AlwaysMatchFlags = alwaysMatchFlags;
                                NeverMatchFlags = neverMatchFlags;
                                Buffer1 = buffer1;
                                Buffer2 = buffer2;
                                PrevSortKey = prev1;
                                PrevCode = -1;
                                QuickCheckPossible = quickCheckPossible;
                        }

                        public readonly CompareOptions Option;
                        public readonly byte* NeverMatchFlags;
                        public readonly byte* AlwaysMatchFlags;
                        public byte* Buffer1;
                        public byte* Buffer2;
                        public int PrevCode;
                        public byte* PrevSortKey;
                        public readonly bool QuickCheckPossible;

                        public void ClearPrevInfo ()
                        {
                                PrevCode = -1;
                                PrevSortKey = null;
                        }
                }

                unsafe struct PreviousInfo
                {
                        public int Code;
                        public byte* SortKey;

                        public PreviousInfo (bool dummy)
                        {
                                Code = -1;
                                SortKey = null;
                        }
                }

                struct Escape
                {
                        public string Source;
                        public int Index;
                        public int Start;
                        public int End;
                        public int Optional;
                }

                static SimpleCollator invariant =
                        new SimpleCollator (CultureInfo.InvariantCulture);

                readonly TextInfo textInfo; // for ToLower().
                readonly bool frenchSort;
                unsafe readonly byte* cjkCatTable;
                unsafe readonly byte* cjkLv1Table;
                readonly CodePointIndexer cjkIndexer;
                unsafe readonly byte* cjkLv2Table;
                readonly CodePointIndexer cjkLv2Indexer;
                readonly int lcid;
                readonly Contraction [] contractions;
                readonly Level2Map [] level2Maps;

                // This flag marks characters as "unsafe", where the character
                // could be used as part of a contraction (whose length > 1).
                readonly byte [] unsafeFlags;

                const int UnsafeFlagLength = 0x300 / 8;

//              readonly byte [] contractionFlags = new byte [16];

                // This array is internally used inside IndexOf() to store
                // "no need to check" ASCII characters.
                //
                // Now that it should be thread safe, this array is allocated
                // at every time.
//              byte [] neverMatchFlags = new byte [128 / 8];

                #region .ctor() and split functions

                public SimpleCollator (CultureInfo culture)
                {
                        lcid = culture.LCID;
                        textInfo = culture.TextInfo;

                        unsafe {
                                SetCJKTable (culture, ref cjkIndexer,
                                        ref cjkCatTable, ref cjkLv1Table,
                                        ref cjkLv2Indexer, ref cjkLv2Table);
                        }

                        // Get tailoring info
                        TailoringInfo t = null;
                        for (CultureInfo ci = culture; ci.LCID != 127; ci = ci.Parent) {
                                t = Uni.GetTailoringInfo (ci.LCID);
                                if (t != null)
                                        break;
                        }
                        if (t == null) // then use invariant
                                t = Uni.GetTailoringInfo (127);

                        frenchSort = t.FrenchSort;
                        Uni.BuildTailoringTables (culture, t, ref contractions,
                                ref level2Maps);
                        unsafeFlags = new byte [UnsafeFlagLength];
                        foreach (Contraction c in contractions) {
                                if (c.Source.Length > 1)
                                        foreach (char ch in c.Source)
                                                unsafeFlags [(int) ch / 8 ]
                                                        |= (byte) (1 << ((int) ch & 7));
//                              for (int i = 0; i < c.Source.Length; i++) {
//                                      int ch = c.Source [i];
//                                      if (ch > 127)
//                                              continue;
//                                      contractionFlags [ch / 8] |= (byte) (1 << (ch & 7));
//                              }
                        }
                        if (lcid != 127)
                                foreach (Contraction c in invariant.contractions) {
                                        if (c.Source.Length > 1)
                                                foreach (char ch in c.Source)
                                                        unsafeFlags [(int) ch / 8 ] 
                                                                |= (byte) (1 << ((int) ch & 7));
//                                      for (int i = 0; i < c.Source.Length; i++) {
//                                              int ch = c.Source [i];
//                                              if (ch > 127)
//                                                      continue;
//                                              contractionFlags [ch / 8] |= (byte) (1 << (ch & 7));
//                                      }
                                }

                        // FIXME: Since tailorings are mostly for latin
                        // (and in some cases Cyrillic) characters, it would
                        // be much better for performance to store "start 
                        // indexes" for > 370 (culture-specific letters).

/*
// dump tailoring table
Console.WriteLine ("******** building table for {0} : contractions - {1} diacritical - {2}",
culture.LCID, contractions.Length, level2Maps.Length);
foreach (Contraction c in contractions) {
foreach (char cc in c.Source)
Console.Write ("{0:X4} ", (int) cc);
Console.WriteLine (" -> '{0}'", c.Replacement);
}
*/
                }

                unsafe private void SetCJKTable (
                        CultureInfo culture, ref CodePointIndexer cjkIndexer,
                        ref byte* catTable, ref byte* lv1Table,
                        ref CodePointIndexer lv2Indexer, ref byte* lv2Table)
                {
                        string name = GetNeutralCulture (culture).Name;

                        Uni.FillCJK (name, ref cjkIndexer, ref catTable,
                                ref lv1Table, ref lv2Indexer, ref lv2Table);
                }

                static CultureInfo GetNeutralCulture (CultureInfo info)
                {
                        CultureInfo ret = info;
                        while (ret.Parent != null && ret.Parent.LCID != 127)
                                ret = ret.Parent;
                        return ret;
                }

                #endregion

                unsafe byte Category (int cp)
                {
                        if (cp < 0x3000 || cjkCatTable == null)
                                return Uni.Category (cp);
                        int idx = cjkIndexer.ToIndex (cp);
                        return idx < 0 ? Uni.Category (cp) : cjkCatTable [idx];
                }

                unsafe byte Level1 (int cp)
                {
                        if (cp < 0x3000 || cjkLv1Table == null)
                                return Uni.Level1 (cp);
                        int idx = cjkIndexer.ToIndex (cp);
                        return idx < 0 ? Uni.Level1 (cp) : cjkLv1Table [idx];
                }

                unsafe byte Level2 (int cp, ExtenderType ext)
                {
                        if (ext == ExtenderType.Buggy)
                                return 5;
                        else if (ext == ExtenderType.Conditional)
                                return 0;

                        if (cp < 0x3000 || cjkLv2Table == null)
                                return Uni.Level2 (cp);
                        int idx = cjkLv2Indexer.ToIndex (cp);
                        byte ret = idx < 0 ? (byte) 0 : cjkLv2Table [idx];
                        if (ret != 0)
                                return ret;
                        ret = Uni.Level2 (cp);
                        if (level2Maps.Length == 0)
                                return ret;
                        for (int i = 0; i < level2Maps.Length; i++) {
                                if (level2Maps [i].Source == ret)
                                        return level2Maps [i].Replace;
                                else if (level2Maps [i].Source > ret)
                                        break;
                        }
                        return ret;
                }

                static bool IsHalfKana (int cp, COpt opt)
                {
                        return (opt & COpt.IgnoreWidth) != 0 ||
                                Uni.IsHalfWidthKana ((char) cp);
                }

                Contraction GetContraction (string s, int start, int end)
                {
//                      int si = s [start];
//                      if (si < 128 && (contractionFlags [si / 8] & (1 << (si & 7))) == 0)
//                              return null;
                        Contraction c = GetContraction (s, start, end, contractions);
                        if (c != null || lcid == 127)
                                return c;
                        return GetContraction (s, start, end, invariant.contractions);
                }

                Contraction GetContraction (string s, int start, int end, Contraction [] clist)
                {
                        for (int i = 0; i < clist.Length; i++) {
                                Contraction ct = clist [i];
                                int diff = ct.Source [0] - s [start];
                                if (diff > 0)
                                        return null; // it's already sorted
                                else if (diff < 0)
                                        continue;
                                char [] chars = ct.Source;
                                if (end - start < chars.Length)
                                        continue;
                                bool match = true;
                                for (int n = 0; n < chars.Length; n++)
                                        if (s [start + n] != chars [n]) {
                                                match = false;
                                                break;
                                        }
                                if (match)
                                        return ct;
                        }
                        return null;
                }

                Contraction GetTailContraction (string s, int start, int end)
                {
//                      int si = s [end - 1];
//                      if (si < 128 && (contractionFlags [si / 8] & (1 << (si & 7))) == 0)
//                              return null;
                        Contraction c = GetTailContraction (s, start, end, contractions);
                        if (c != null || lcid == 127)
                                return c;
                        return GetTailContraction (s, start, end, invariant.contractions);
                }

                Contraction GetTailContraction (string s, int start, int end, Contraction [] clist)
                {
                        if (start == end || end < -1 || start >= s.Length || s.Length <= end + 1)
                                throw new SystemException (String.Format ("MONO internal error. Failed to get TailContraction. start = {0} end = {1} string = '{2}'", start, end, s));
                        for (int i = 0; i < clist.Length; i++) {
                                Contraction ct = clist [i];
                                char [] chars = ct.Source;
                                if (chars.Length > start - end)
                                        continue;
                                if (chars [chars.Length - 1] != s [start])
                                        continue;

                                bool match = true;
                                for (int n = 0, spos = start - chars.Length + 1;
                                     n < chars.Length;
                                     n++, spos++) {
                                        if (s [spos] != chars [n]) {
                                                match = false;
                                                break;
                                        }
                                }
                                if (match)
                                        return ct;
                        }
                        return null;
                }

                Contraction GetContraction (char c)
                {
                        Contraction ct = GetContraction (c, contractions);
                        if (ct != null || lcid == 127)
                                return ct;
                        return GetContraction (c, invariant.contractions);
                }

                Contraction GetContraction (char c, Contraction [] clist)
                {
                        for (int i = 0; i < clist.Length; i++) {
                                Contraction ct = clist [i];
                                if (ct.Source [0] > c)
                                        return null; // it's already sorted
                                if (ct.Source [0] == c && ct.Source.Length == 1)
                                        return ct;
                        }
                        return null;
                }

                int FilterOptions (int i, COpt opt)
                {
                        if ((opt & COpt.IgnoreWidth) != 0) {
                                int x = Uni.ToWidthCompat (i);
                                if (x != 0)
                                        i = x;
                        }
                        if ((opt & COpt.OrdinalIgnoreCase) != 0)
                                i = textInfo.ToLower ((char) i);
                        if ((opt & COpt.IgnoreCase) != 0)
                                i = textInfo.ToLower ((char) i);
                        if ((opt & COpt.IgnoreKanaType) != 0)
                                i = Uni.ToKanaTypeInsensitive (i);
                        return i;
                }

                enum ExtenderType {
                        None,
                        Simple,
                        Voiced,
                        Conditional,
                        Buggy,
                }

                ExtenderType GetExtenderType (int i)
                {
                        // LAMESPEC: Windows expects true for U+3005, but 
                        // sometimes it does not represent to repeat just
                        // one character.
                        // Windows also expects true for U+3031 and U+3032,
                        // but they should *never* repeat one character.

                        // U+2015 becomes an extender only when it is Japanese
                        if (i == 0x2015)
                                return lcid == 16 ? ExtenderType.Conditional :
                                        ExtenderType.None;

                        if (i < 0x3005 || i > 0xFF70)
                                return ExtenderType.None;
                        if (i >= 0xFE7C) {
                                switch (i) {
                                case 0xFE7C:
                                case 0xFE7D:
                                        return ExtenderType.Simple;
                                case 0xFF70:
                                        return ExtenderType.Conditional;
                                case 0xFF9E:
                                case 0xFF9F:
                                        return ExtenderType.Voiced;
                                }
                        }
                        if (i > 0x30FE)
                                return ExtenderType.None;
                        switch (i) {
                        case 0x3005: // LAMESPEC: see above.
                                return ExtenderType.Buggy;
                        case 0x3031: // LAMESPEC: see above.
                        case 0x3032: // LAMESPEC: see above.
                        case 0x309D:
                        case 0x30FD:
                                return ExtenderType.Simple;
                        case 0x309E:
                        case 0x30FE:
                                return ExtenderType.Voiced;
                        case 0x30FC:
                                return ExtenderType.Conditional;
                        default:
                                return ExtenderType.None;
                        }
                }

                static byte ToDashTypeValue (ExtenderType ext, COpt opt)
                {
                        if ((opt & COpt.IgnoreNonSpace) != 0) // LAMESPEC: huh, why?
                                return 3;
                        switch (ext) {
                        case ExtenderType.None:
                                return 3;
                        case ExtenderType.Conditional:
                                return 5;
                        default:
                                return 4;
                        }
                }

                int FilterExtender (int i, ExtenderType ext, COpt opt)
                {
                        if (ext == ExtenderType.Conditional &&
                                Uni.HasSpecialWeight ((char) i)) {
                                bool half = IsHalfKana ((char) i, opt);
                                bool katakana = !Uni.IsHiragana ((char) i);
                                switch (Level1 (i) & 7) {
                                case 2:
                                        return half ? 0xFF71 : katakana ? 0x30A2 : 0x3042;
                                case 3:
                                        return half ? 0xFF72 : katakana ? 0x30A4 : 0x3044;
                                case 4:
                                        return half ? 0xFF73 : katakana ? 0x30A6 : 0x3046;
                                case 5:
                                        return half ? 0xFF74 : katakana ? 0x30A8 : 0x3048;
                                case 6:
                                        return half ? 0xFF75 : katakana ? 0x30AA : 0x304A;
                                }
                        }
                        return i;
                }

                static bool IsIgnorable (int i, COpt opt)
                {
                        return Uni.IsIgnorable (i, (byte) (1 +
                                ((opt & COpt.IgnoreSymbols) != 0 ? 2 : 0) +
                                ((opt & COpt.IgnoreNonSpace) != 0 ? 4 : 0)));
                        
                }

                bool IsSafe (int i)
                {
                        return i / 8 >= unsafeFlags.Length ? true : (unsafeFlags [i / 8] & (1 << (i % 8))) == 0;
                }

                #region GetSortKey()

                public SortKey GetSortKey (string s)
                {
                        return GetSortKey (s, CompareOptions.None);
                }

                public SortKey GetSortKey (string s, CompareOptions options)
                {
                        return GetSortKey (s, 0, s.Length, options);
                }

                public SortKey GetSortKey (string s, int start, int length, CompareOptions options)
                {
                        SortKeyBuffer buf = new SortKeyBuffer (lcid);
                        buf.Initialize (options, lcid, s, frenchSort);
                        int end = start + length;
                        GetSortKey (s, start, end, buf, options);
                        return buf.GetResultAndReset ();
                }

                unsafe void GetSortKey (string s, int start, int end,
                        SortKeyBuffer buf, CompareOptions opt)
                {
                        byte* prevbuf = stackalloc byte [4];
                        ClearBuffer (prevbuf, 4);
                        Context ctx = new Context (opt, null, null, null, null, prevbuf, false);

                        for (int n = start; n < end; n++) {
                                int i = s [n];

                                ExtenderType ext = GetExtenderType (i);
                                if (ext != ExtenderType.None) {
                                        i = FilterExtender (ctx.PrevCode, ext, opt);
                                        if (i >= 0)
                                                FillSortKeyRaw (i, ext, buf, opt);
                                        else if (ctx.PrevSortKey != null) {
                                                byte* b = ctx.PrevSortKey;
                                                buf.AppendNormal (
                                                        b [0],
                                                        b [1],
                                                        b [2] != 1 ? b [2] : Level2 (i, ext),
                                                        b [3] != 1 ? b [3] : Uni.Level3 (i));
                                        }
                                        // otherwise do nothing.
                                        // (if the extender is the first char
                                        // in the string, then just ignore.)
                                        continue;
                                }

                                if (IsIgnorable (i, opt))
                                        continue;
                                i = FilterOptions (i, opt);

                                Contraction ct = GetContraction (s, n, end);
                                if (ct != null) {
                                        if (ct.Replacement != null) {
                                                GetSortKey (ct.Replacement, 0, ct.Replacement.Length, buf, opt);
                                        } else {
                                                byte* b = ctx.PrevSortKey;
                                                for (int bi = 0; bi < ct.SortKey.Length; bi++)
                                                        b [bi] = ct.SortKey [bi];
                                                buf.AppendNormal (
                                                        b [0],
                                                        b [1],
                                                        b [2] != 1 ? b [2] : Level2 (i, ext),
                                                        b [3] != 1 ? b [3] : Uni.Level3 (i));
                                                ctx.PrevCode = -1;
                                        }
                                        n += ct.Source.Length - 1;
                                }
                                else {
                                        if (!Uni.IsIgnorableNonSpacing (i))
                                                ctx.PrevCode = i;
                                        FillSortKeyRaw (i, ExtenderType.None, buf, opt);
                                }
                        }
                }

                void FillSortKeyRaw (int i, ExtenderType ext,
                        SortKeyBuffer buf, CompareOptions opt)
                {
                        if (0x3400 <= i && i <= 0x4DB5) {
                                int diff = i - 0x3400;
                                buf.AppendCJKExtension (
                                        (byte) (0x10 + diff / 254),
                                        (byte) (diff % 254 + 2));
                                return;
                        }

                        UnicodeCategory uc = char.GetUnicodeCategory ((char) i);
                        switch (uc) {
                        case UnicodeCategory.PrivateUse:
                                int diff = i - 0xE000;
                                buf.AppendNormal (
                                        (byte) (0xE5 + diff / 254),
                                        (byte) (diff % 254 + 2),
                                        0,
                                        0);
                                return;
                        case UnicodeCategory.Surrogate:
                                FillSurrogateSortKeyRaw (i, buf);
                                return;
                        }

                        byte level2 = Level2 (i, ext);
                        if (Uni.HasSpecialWeight ((char) i)) {
                                byte level1 = Level1 (i);
                                buf.AppendKana (
                                        Category (i),
                                        level1,
                                        level2,
                                        Uni.Level3 (i),
                                        Uni.IsJapaneseSmallLetter ((char) i),
                                        ToDashTypeValue (ext, opt),
                                        !Uni.IsHiragana ((char) i),
                                        IsHalfKana ((char) i, opt)
                                        );
                                if ((opt & COpt.IgnoreNonSpace) == 0 && ext == ExtenderType.Voiced)
                                        // Append voice weight
                                        buf.AppendNormal (1, 1, 1, 0);
                        }
                        else
                                buf.AppendNormal (
                                        Category (i),
                                        Level1 (i),
                                        level2,
                                        Uni.Level3 (i));
                }

                void FillSurrogateSortKeyRaw (int i, SortKeyBuffer buf)
                {
                        int diffbase = 0;
                        int segment = 0;
                        byte lower = 0;

                        if (i < 0xD840) {
                                diffbase = 0xD800;
                                segment = 0x41;
                                lower = (byte) ((i == 0xD800) ? 0x3E : 0x3F);
                        } else if (0xD840 <= i && i < 0xD880) {
                                diffbase = 0xD840;
                                segment = 0xF2;
                                lower = 0x3E;
                        } else if (0xDB80 <= i && i < 0xDC00) {
                                diffbase = 0xDB80 - 0x40;
                                segment = 0xFE;
                                lower = 0x3E;
                        } else {
                                diffbase = 0xDC00 - 0xF8 + 2;
                                segment = 0x41;
                                lower = 0x3F;
                        }
                        int diff = i - diffbase;

                        buf.AppendNormal (
                                (byte) (segment + diff / 254),
                                (byte) (diff % 254 + 2),
                                lower,
                                lower);
                }

                #endregion

                #region Compare()

                public int Compare (string s1, string s2)
                {
                        return Compare (s1, s2, CompareOptions.None);
                }

                public int Compare (string s1, string s2, CompareOptions options)
                {
                        return Compare (s1, 0, s1.Length, s2, 0, s2.Length, options);
                }

                private int CompareOrdinal (string s1, int idx1, int len1,
                        string s2, int idx2, int len2)
                {
                        int min = len1 < len2 ? len1 : len2;
                        int end1 = idx1 + min;
                        int end2 = idx2 + min;
                        if (idx1 < 0 || idx2 < 0 || end1 > s1.Length || end2 > s2.Length)
                                throw new SystemException (String.Format ("CompareInfo Internal Error: Should not happen. {0} {1} {2} {3} {4} {5}", idx1, idx2, len1, len2, s1.Length, s2.Length));
                        for (int i1 = idx1, i2 = idx2;
                                i1 < end1 && i2 < end2; i1++, i2++)
                                if (s1 [i1] != s2 [i2])
                                        return s1 [i1] - s2 [i2];
                        return len1 == len2 ? 0 :
                                len1 == min ? - 1 : 1;
                }

                // mostly equivalent to CompareOrdinal, but the return value is
                // not based on codepoints.
                private int CompareQuick (string s1, int idx1, int len1,
                        string s2, int idx2, int len2, out bool sourceConsumed,
                        out bool targetConsumed, bool immediateBreakup)
                {
                        sourceConsumed = false;
                        targetConsumed = false;
                        int min = len1 < len2 ? len1 : len2;
                        int end1 = idx1 + min;
                        int end2 = idx2 + min;
                        if (idx1 < 0 || idx2 < 0 || end1 > s1.Length || end2 > s2.Length)
                                throw new SystemException (String.Format ("CompareInfo Internal Error: Should not happen. {0} {1} {2} {3} {4} {5}", idx1, idx2, len1, len2, s1.Length, s2.Length));
                        for (int i1 = idx1, i2 = idx2;
                                i1 < end1 && i2 < end2; i1++, i2++)
                                if (s1 [i1] != s2 [i2]) {
                                        if (immediateBreakup)
                                                return -1;
                                        int ret = Category (s1 [i1]) - Category (s2 [i2]);
                                        if (ret == 0)
                                                ret = Level1 (s1 [i1]) - Level1 (s2 [i2]);
                                        // no level2 and 4
                                        if (ret == 0)
                                                ret = Uni.Level3 (s1 [i1]) - Uni.Level3 (s2 [i2]);
                                        if (ret == 0)
                                                throw new SystemException (String.Format ("CompareInfo Internal Error: Should not happen. '{0}' {2} {3} '{1}' {4} {5}", s1, s2, idx1, end1, idx2, end2));
                                        return ret;
                                }
                        sourceConsumed = len1 <= len2;
                        targetConsumed = len1 >= len2;
                        return len1 == len2 ? 0 :
                                len1 == min ? - 1 : 1;
                }

                private int CompareOrdinalIgnoreCase (string s1, int idx1, int len1,
                        string s2, int idx2, int len2)
                {
                        int min = len1 < len2 ? len1 : len2;
                        int end1 = idx1 + min;
                        int end2 = idx2 + min;
                        if (idx1 < 0 || idx2 < 0 || end1 > s1.Length || end2 > s2.Length)
                                throw new SystemException (String.Format ("CompareInfo Internal Error: Should not happen. {0} {1} {2} {3} {4} {5}", idx1, idx2, len1, len2, s1.Length, s2.Length));
                        TextInfo ti = invariant.textInfo;
                        for (int i1 = idx1, i2 = idx2;
                                i1 < end1 && i2 < end2; i1++, i2++)
                                if (ti.ToLower (s1 [i1]) != ti.ToLower (s2 [i2]))
                                        return ti.ToLower (s1 [i1]) - ti.ToLower (s2 [i2]);
                        return len1 == len2 ? 0 :
                                len1 == min ? - 1 : 1;
                }

                public unsafe int Compare (string s1, int idx1, int len1,
                        string s2, int idx2, int len2, CompareOptions options)
                {
                        // quick equality check
                        if (idx1 == idx2 && len1 == len2 &&
                                Object.ReferenceEquals (s1, s2))
                                return 0;
                        if (options == CompareOptions.Ordinal)
                                return CompareOrdinal (s1, idx1, len1, s2, idx2, len2);
                        if (options == CompareOptions.OrdinalIgnoreCase)
                                return CompareOrdinalIgnoreCase (s1, idx1, len1, s2, idx2, len2);

#if false // stable easy version, depends on GetSortKey().
                        SortKey sk1 = GetSortKey (s1, idx1, len1, options);
                        SortKey sk2 = GetSortKey (s2, idx2, len2, options);
                        byte [] d1 = sk1.KeyData;
                        byte [] d2 = sk2.KeyData;
                        int len = d1.Length > d2.Length ? d2.Length : d1.Length;
                        for (int i = 0; i < len; i++)
                                if (d1 [i] != d2 [i])
                                        return d1 [i] < d2 [i] ? -1 : 1;
                        return d1.Length == d2.Length ? 0 : d1.Length < d2.Length ? -1 : 1;
#else
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        Context ctx = new Context (options, null, null, sk1, sk2, null,
                                QuickCheckPossible (s1, idx1, idx1 + len1, s2, idx2, idx2 + len2));

                        bool dummy, dummy2;
                        int ret = CompareInternal (s1, idx1, len1, s2, idx2, len2, out dummy, out dummy2, true, false, ref ctx);
                        return ret == 0 ? 0 : ret < 0 ? -1 : 1;
#endif
                }

                unsafe void ClearBuffer (byte* buffer, int size)
                {
                        for (int i = 0; i < size; i++)
                                buffer [i] = 0;
                }

                bool QuickCheckPossible (string s1, int idx1, int end1,
                        string s2, int idx2, int end2)
                {
#if true
                        // looks like it is buggy and inefficient, so just disable it.
                        return false;
#else
                        if (QuickCheckDisabled)
                                return false;
//                      if (s1.Length > 100 || s2.Length > 100)
//                              return false;
                        for (int i = idx1; i < end1; i++)
                                if (s1 [i] < 0x20 && (s1 [i] < '\x9' || s1 [i] > '\xD') || s1 [i] >= 0x80 || s1 [i] == '-' || s1 [i] == '\'')
                                        return false;
                        for (int i = idx2; i < end2; i++)
                                if (s2 [i] < 0x20 && (s2 [i] < '\x9' || s2 [i] > '\xD') || s2 [i] >= 0x80 || s2 [i] == '-' || s2 [i] == '\'')
                                        return false;
                        return true;
#endif
                }

                unsafe int CompareInternal (string s1, int idx1, int len1, string s2,
                        int idx2, int len2,
                        out bool targetConsumed, out bool sourceConsumed,
                        bool skipHeadingExtenders, bool immediateBreakup,
                        ref Context ctx)
                {
                        COpt opt = ctx.Option;
                        int start1 = idx1;
                        int start2 = idx2;
                        int end1 = idx1 + len1;
                        int end2 = idx2 + len2;
                        targetConsumed = false;
                        sourceConsumed = false;
                        PreviousInfo prev2 = new PreviousInfo (false);

                        if (opt == CompareOptions.None && ctx.QuickCheckPossible)
                                return CompareQuick (s1, idx1, len1, s2, idx2, len2, out sourceConsumed, out targetConsumed, immediateBreakup);

                        // It holds final result that comes from the comparison
                        // at level 2 or lower. Even if Compare() found the
                        // difference at level 2 or lower, it still has to
                        // continue level 1 comparison. FinalResult is used
                        // when there was no further differences.
                        int finalResult = 0;
                        // It holds the comparison level to do. It starts from
                        // 5, and becomes 1 when we do primary-only comparison.
                        int currentLevel = 5;

                        int lv5At1 = -1;
                        int lv5At2 = -1;
                        int lv5Value1 = 0;
                        int lv5Value2 = 0;

                        // Skip heading extenders
                        if (skipHeadingExtenders) {
                                for (; idx1 < end1; idx1++)
                                        if (GetExtenderType (s1 [idx1]) == ExtenderType.None)
                                                break;
                                for (; idx2 < end2; idx2++)
                                        if (GetExtenderType (s2 [idx2]) == ExtenderType.None)
                                                break;
                        }

                        ExtenderType ext1 = ExtenderType.None;
                        ExtenderType ext2 = ExtenderType.None;

                        int quickCheckPos1 = idx1;
                        int quickCheckPos2 = idx2;
                        bool stringSort = (opt & COpt.StringSort) != 0;
                        bool ignoreNonSpace = (opt & COpt.IgnoreNonSpace) != 0;
                        Escape escape1 = new Escape ();
                        Escape escape2 = new Escape ();

                        while (true) {
                                for (; idx1 < end1; idx1++)
                                        if (!IsIgnorable (s1 [idx1], opt))
                                                break;
                                for (; idx2 < end2; idx2++)
                                        if (!IsIgnorable (s2 [idx2], opt))
                                                break;

                                if (idx1 >= end1) {
                                        if (escape1.Source == null)
                                                break;
                                        s1 = escape1.Source;
                                        start1 = escape1.Start;
                                        idx1 = escape1.Index;
                                        end1 = escape1.End;
                                        quickCheckPos1 = escape1.Optional;
                                        escape1.Source = null;
                                        continue;
                                }
                                if (idx2 >= end2) {
                                        if (escape2.Source == null)
                                                break;
                                        s2 = escape2.Source;
                                        start2 = escape2.Start;
                                        idx2 = escape2.Index;
                                        end2 = escape2.End;
                                        quickCheckPos2 = escape2.Optional;
                                        escape2.Source = null;
                                        continue;
                                }
#if true
// If comparison is unstable, then this part is one of the most doubtful part.
// Here we run quick codepoint comparison and run back to "stable" area to
// compare characters.

                                // Strictly to say, even the first character
                                // could be compared here, but it messed
                                // backward step, so I just avoided mess.
                                if (quickCheckPos1 < idx1 && quickCheckPos2 < idx2) {
                                        while (idx1 < end1 && idx2 < end2 &&
                                                s1 [idx1] == s2 [idx2]) {
                                                idx1++;
                                                idx2++;
                                        }
                                        if (idx1 == end1 || idx2 == end2)
                                                continue; // check replacement

                                        int backwardEnd1 = quickCheckPos1;
                                        int backwardEnd2 = quickCheckPos2;
                                        quickCheckPos1 = idx1;
                                        quickCheckPos2 = idx2;

                                        idx1--;
                                        idx2--;

                                        for (;idx1 > backwardEnd1; idx1--)
                                                if (Category (s1 [idx1]) != 1)
                                                        break;
                                        for (;idx2 > backwardEnd2; idx2--)
                                                if (Category (s2 [idx2]) != 1)
                                                        break;
                                        for (;idx1 > backwardEnd1; idx1--)
                                                if (IsSafe (s1 [idx1]))
                                                        break;
                                        for (;idx2 > backwardEnd2; idx2--)
                                                if (IsSafe (s2 [idx2]))
                                                        break;
                                }
#endif

                                int cur1 = idx1;
                                int cur2 = idx2;
                                byte* sk1 = null;
                                byte* sk2 = null;
                                int i1 = FilterOptions (s1 [idx1], opt);
                                int i2 = FilterOptions (s2 [idx2], opt);
                                bool special1 = false;
                                bool special2 = false;

                                // If current character is an expander, then
                                // repeat the previous character.
                                ext1 = GetExtenderType (i1);
                                if (ext1 != ExtenderType.None) {
                                        if (ctx.PrevCode < 0) {
                                                if (ctx.PrevSortKey == null) {
                                                        // nothing to extend
                                                        idx1++;
                                                        continue;
                                                }
                                                sk1 = ctx.PrevSortKey;
                                        }
                                        else
                                                i1 = FilterExtender (ctx.PrevCode, ext1, opt);
                                }
                                ext2 = GetExtenderType (i2);
                                if (ext2 != ExtenderType.None) {
                                        if (prev2.Code < 0) {
                                                if (prev2.SortKey == null) {
                                                        // nothing to extend
                                                        idx2++;
                                                        continue;
                                                }
                                                sk2 = prev2.SortKey;
                                        }
                                        else
                                                i2 = FilterExtender (prev2.Code, ext2, opt);
                                }

                                byte cat1 = Category (i1);
                                byte cat2 = Category (i2);

                                // Handle special weight characters
                                if (cat1 == 6) {
                                        if (!stringSort && currentLevel == 5) {
                                                lv5At1 = escape1.Source != null ?
                                                        escape1.Index - escape1.Start :
                                                        cur1 - start1;
                                                // here Windows has a bug that it does
                                                // not consider thirtiary weight.
                                                lv5Value1 = Level1 (i1) << 8 + Uni.Level3 (i1);
                                        }
                                        ctx.PrevCode = i1;
                                        idx1++;
                                }
                                if (cat2 == 6) {
                                        if (!stringSort && currentLevel == 5) {
                                                lv5At2 = escape2.Source != null ?
                                                        escape2.Index - escape2.Start :
                                                        cur2 - start2;
                                                // here Windows has a bug that it does
                                                // not consider thirtiary weight.
                                                lv5Value2 = Level1 (i2) << 8 + Uni.Level3 (i2);
                                        }
                                        prev2.Code = i2;
                                        idx2++;
                                }
                                if (cat1 == 6 || cat2 == 6) {
                                        if (currentLevel == 5) {
                                                if (lv5Value1 == lv5Value2) {
                                                        // There is not really difference here.
                                                        lv5At1 = lv5At2 = -1;
                                                        lv5Value1 = lv5Value2 = 0;
                                                }
                                                else
                                                        currentLevel = 4;
                                        }
                                        continue;
                                }

                                Contraction ct1 = null;
                                if (ext1 == ExtenderType.None)
                                        ct1 = GetContraction (s1, idx1, end1);

                                int offset1 = 1;
                                if (sk1 != null)
                                        offset1 = 1;
                                else if (ct1 != null) {
                                        offset1 = ct1.Source.Length;
                                        if (ct1.SortKey != null) {
                                                sk1 = ctx.Buffer1;
                                                for (int i = 0; i < ct1.SortKey.Length; i++)
                                                        sk1 [i] = ct1.SortKey [i];
                                                ctx.PrevCode = -1;
                                                ctx.PrevSortKey = sk1;
                                        }
                                        else if (escape1.Source == null) {
                                                escape1.Source = s1;
                                                escape1.Start = start1;
                                                escape1.Index = cur1 + ct1.Source.Length;
                                                escape1.End = end1;
                                                escape1.Optional = quickCheckPos1;
                                                s1 = ct1.Replacement;
                                                idx1 = 0;
                                                start1 = 0;
                                                end1 = s1.Length;
                                                quickCheckPos1 = 0;
                                                continue;
                                        }
                                }
                                else {
                                        sk1 = ctx.Buffer1;
                                        sk1 [0] = cat1;
                                        sk1 [1] = Level1 (i1);
                                        if (!ignoreNonSpace && currentLevel > 1)
                                                sk1 [2] = Level2 (i1, ext1);
                                        if (currentLevel > 2)
                                                sk1 [3] = Uni.Level3 (i1);
                                        if (currentLevel > 3)
                                                special1 = Uni.HasSpecialWeight ((char) i1);
                                        if (cat1 > 1)
                                                ctx.PrevCode = i1;
                                }

                                Contraction ct2 = null;
                                if (ext2 == ExtenderType.None)
                                        ct2 = GetContraction (s2, idx2, end2);

                                if (sk2 != null)
                                        idx2++;
                                else if (ct2 != null) {
                                        idx2 += ct2.Source.Length;
                                        if (ct2.SortKey != null) {
                                                sk2 = ctx.Buffer2;
                                                for (int i = 0; i < ct2.SortKey.Length; i++)
                                                        sk2 [i] = ct2.SortKey [i];
                                                prev2.Code = -1;
                                                prev2.SortKey = sk2;
                                        }
                                        else if (escape2.Source == null) {
                                                escape2.Source = s2;
                                                escape2.Start = start2;
                                                escape2.Index = cur2 + ct2.Source.Length;
                                                escape2.End = end2;
                                                escape2.Optional = quickCheckPos2;
                                                s2 = ct2.Replacement;
                                                idx2 = 0;
                                                start2 = 0;
                                                end2 = s2.Length;
                                                quickCheckPos2 = 0;
                                                continue;
                                        }
                                }
                                else {
                                        sk2 = ctx.Buffer2;
                                        sk2 [0] = cat2;
                                        sk2 [1] = Level1 (i2);
                                        if (!ignoreNonSpace && currentLevel > 1)
                                                sk2 [2] = Level2 (i2, ext2);
                                        if (currentLevel > 2)
                                                sk2 [3] = Uni.Level3 (i2);
                                        if (currentLevel > 3)
                                                special2 = Uni.HasSpecialWeight ((char) i2);
                                        if (cat2 > 1)
                                                prev2.Code = i2;
                                        idx2++;
                                }

                                // Add offset here so that it does not skip
                                // idx1 while s2 has a replacement.
                                idx1 += offset1;

                                if (!ignoreNonSpace) {
                                        // add diacritical marks in s1 here
                                        while (idx1 < end1) {
                                                if (Category (s1 [idx1]) != 1)
                                                        break;
                                                if (sk1 [2] == 0)
                                                        sk1 [2] = 2;
                                                sk1 [2] = (byte) (sk1 [2] + 
                                                        Level2 (s1 [idx1], ExtenderType.None));
                                                idx1++;
                                        }

                                        // add diacritical marks in s2 here
                                        while (idx2 < end2) {
                                                if (Category (s2 [idx2]) != 1)
                                                        break;
                                                if (sk2 [2] == 0)
                                                        sk2 [2] = 2;
                                                sk2 [2] = (byte) (sk2 [2] + 
                                                        Level2 (s2 [idx2], ExtenderType.None));
                                                idx2++;
                                        }
                                }

                                int ret = sk1 [0] - sk2 [0];
                                ret = ret != 0 ? ret : sk1 [1] - sk2 [1];
                                if (ret != 0)
                                        return ret;
                                if (currentLevel == 1)
                                        continue;
                                if (!ignoreNonSpace) {
                                        ret = sk1 [2] - sk2 [2];
                                        if (ret != 0) {
                                                finalResult = ret;
                                                if (immediateBreakup)
                                                        return -1; // different
                                                currentLevel = frenchSort ? 2 : 1;
                                                continue;
                                        }
                                }
                                if (currentLevel == 2)
                                        continue;
                                ret = sk1 [3] - sk2 [3];
                                if (ret != 0) {
                                        finalResult = ret;
                                        if (immediateBreakup)
                                                return -1; // different
                                        currentLevel = 2;
                                        continue;
                                }
                                if (currentLevel == 3)
                                        continue;
                                if (special1 != special2) {
                                        if (immediateBreakup)
                                                return -1; // different
                                        finalResult = special1 ? 1 : -1;
                                        currentLevel = 3;
                                        continue;
                                }
                                if (special1) {
                                        ret = CompareFlagPair (
                                                !Uni.IsJapaneseSmallLetter ((char) i1),
                                                !Uni.IsJapaneseSmallLetter ((char) i2));
                                        ret = ret != 0 ? ret :
                                                ToDashTypeValue (ext1, opt) -
                                                ToDashTypeValue (ext2, opt);
                                        ret = ret != 0 ? ret : CompareFlagPair (
                                                Uni.IsHiragana ((char) i1),
                                                Uni.IsHiragana ((char) i2));
                                        ret = ret != 0 ? ret : CompareFlagPair (
                                                !IsHalfKana ((char) i1, opt),
                                                !IsHalfKana ((char) i2, opt));
                                        if (ret != 0) {
                                                if (immediateBreakup)
                                                        return -1; // different
                                                finalResult = ret;
                                                currentLevel = 3;
                                                continue;
                                        }
                                }
                        }

                        // If there were only level 3 or lower differences,
                        // then we still have to find diacritical differences
                        // if any.
                        if (!ignoreNonSpace &&
                                finalResult != 0 && currentLevel > 2) {
                                while (idx1 < end1 && idx2 < end2) {
                                        if (!Uni.IsIgnorableNonSpacing (s1 [idx1]))
                                                break;
                                        if (!Uni.IsIgnorableNonSpacing (s2 [idx2]))
                                                break;
                                        finalResult = Level2 (FilterOptions (s1 [idx1], opt), ext1) - Level2 (FilterOptions (s2 [idx2], opt), ext2);
                                        if (finalResult != 0)
                                                break;
                                        idx1++;
                                        idx2++;
                                        // they should work only for the first character
                                        ext1 = ExtenderType.None;
                                        ext2 = ExtenderType.None;
                                }
                        }
                        if (currentLevel == 1 && finalResult != 0) {
                                while (idx1 < end1) {
                                        if (Uni.IsIgnorableNonSpacing (s1 [idx1]))
                                                idx1++;
                                        else
                                                break;
                                }
                                while (idx2 < end2) {
                                        if (Uni.IsIgnorableNonSpacing (s2 [idx2]))
                                                idx2++;
                                        else
                                                break;
                                }
                        }
                        // we still have to check level 5
                        if (finalResult == 0) {
                                if (lv5At1 < 0 && lv5At2 >= 0)
                                        finalResult = -1;
                                else if (lv5At2 < 0 && lv5At1 >= 0)
                                        finalResult = 1;
                                else {
                                        finalResult = lv5At1 - lv5At2;
                                        if (finalResult == 0)
                                                finalResult = lv5Value1 - lv5Value2;
                                }
                        }
                        if (finalResult == 0) {
                                if (idx2 == end2)
                                        targetConsumed = true;
                                if (idx1 == end1)
                                        sourceConsumed = true;
                        }
                        return idx1 != end1 ? 1 : idx2 == end2 ? finalResult : -1;
                }

                int CompareFlagPair (bool b1, bool b2)
                {
                        return b1 == b2 ? 0 : b1 ? 1 : -1;
                }

                #endregion

                #region IsPrefix() and IsSuffix()

                public bool IsPrefix (string src, string target, CompareOptions opt)
                {
                        return IsPrefix (src, target, 0, src.Length, opt);
                }

                public unsafe bool IsPrefix (string s, string target, int start, int length, CompareOptions opt)
                {
                        if (target.Length == 0)
                                return true;
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        Context ctx = new Context (opt, null, null, sk1, sk2, null,
                                QuickCheckPossible (s, start, start + length, target, 0, target.Length));
                        return IsPrefix (s, target, start, length, true, ref ctx);
                }

                unsafe bool IsPrefix (string s, string target, int start, int length, bool skipHeadingExtenders, ref Context ctx)
                {
                        bool consumed, dummy;
                        CompareInternal (s, start, length,
                                target, 0, target.Length,
                                out consumed, out dummy, skipHeadingExtenders,
                                true, ref ctx);
                        return consumed;
                }

                // IsSuffix()

                public bool IsSuffix (string src, string target, CompareOptions opt)
                {
                        return IsSuffix (src, target, src.Length - 1, src.Length, opt);
                }

                public unsafe bool IsSuffix (string s, string target, int start, int length, CompareOptions opt)
                {
                        if (target.Length == 0)
                                return true;
                        int last = LastIndexOf (s, target, start, length, opt);
                        return last >= 0 && Compare (s, last, s.Length - last, target, 0, target.Length, opt) == 0;
/*
                        // quick check : simple codepoint comparison
                        if (s.Length >= target.Length) {
                                int si = start;
                                int se = start - length;
                                for (int i = target.Length - 1; si >= se && i >= 0; i--, si--)
                                        if (s [si] != target [i])
                                                break;
                                if (si == start + target.Length)
                                        return true;
                        }

                        PreviousInfo prev = new PreviousInfo (false);
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        return IsSuffix (opt, s, target, start, length, ref prev, sk1, sk2);
*/
                }
/*
                unsafe bool IsSuffix (string s, string t, int start, int length, ref Context ctx)
                {
                        int tstart = 0;
                        COpt opt = ctx.Option;

                        for (;tstart < t.Length; tstart++)
                                if (!IsIgnorable (t [tstart], opt))
                                        break;
                        if (tstart == t.Length)
                                return true; // as if target is String.Empty.

#if false
// This is still not working. If it is not likely to get working, then just remove it.
                        int si = start;
                        int send = start - length;
                        int ti = t.Length - 1;
                        int tend = -1;

                        int sStep = start + 1;
                        int tStep = t.Length;
                        bool sourceConsumed, targetConsumed;
                        while (true) {
                                for (; send < si; si--)
                                        if (!IsIgnorable (s [si]))
                                                break;
                                for (; tend < ti; ti--)
                                        if (!IsIgnorable (t [ti]))
                                                break;
                                if (tend == ti)
                                        break;
                                for (; send < si; si--)
                                        if (IsSafe (s [si]))
                                                break;
                                for (; tend < ti; ti--)
                                        if (IsSafe (t [ti]))
                                                break;
Console.WriteLine ("==== {0} {1} {2} {3} {4} {5} {6} {7} {8}", s, si, send, length, t, ti, tstart, sStep - si, tStep - ti);
                                if (CompareInternal (opt, s, si, sStep - si,
                                        t, ti, tStep - ti,
                                        out targetConsumed, out sourceConsumed,
                                        true) != 0)
                                        return false;
                                if (send == si)
                                        return false;
                                sStep = si;
                                tStep = ti;
                                si--;
                                ti--;
                        }
                        return true;
#else
                        // FIXME: it is not efficient for very long target.
                        bool sourceConsumed, targetConsumed;
                        int mismatchCount = 0;
                        for (int i = 0; i < length; i++) {
                                ctx.ClearPrevInfo ();

                                int ret = CompareInternal (s, start - i, i + 1,
                                        t, tstart, t.Length - tstart,
                                        out targetConsumed,
                                        // FIXME: could immediately breakup
                                        out sourceConsumed, true, true, ref ctx);
                                if (ret == 0)
                                        return true;
                                if (!sourceConsumed && targetConsumed)
                                        return false;
                                if (!targetConsumed) {
                                        mismatchCount++;
                                        if (mismatchCount > Uni.MaxExpansionLength)
                                                // The largest length of an
                                                // expansion is 3, so if the
                                                // target was not consumed more
                                                // than 3 times, then the tail
                                                // character does not match.
                                                return false;
                                }
                        }
                        return false;
#endif
                }
*/
                #endregion

                #region IndexOf() / LastIndexOf()

                // string

                public int IndexOf (string s, string target, CompareOptions opt)
                {
                        return IndexOf (s, target, 0, s.Length, opt);
                }

                int QuickIndexOf (string s, string target, int start, int length, out bool testWasUnable)
                {
                        int testedSourcePos = -1, testedTargetPos = -1;

                        testWasUnable = true;
                        if (target.Length == 0)
                                return 0;
                        else if (target.Length > length)
                                return -1;
                        testWasUnable = false;

                        int end = start + length - target.Length + 1;
                        for (int i = start; i < end; i++) {
                                bool no = false;
                                for (int j = 0; j < target.Length; j++) {
                                        if (testedTargetPos < j) {
                                                if (target [j] >= 0x80) {
                                                        testWasUnable = true;
                                                        return -1;
                                                }
                                                else
                                                        testedTargetPos = j;
                                        }
                                        if (testedSourcePos < i + j) {
                                                if (s [i + j] >= 0x80) {
                                                        testWasUnable = true;
                                                        return -1;
                                                }
                                                else
                                                        testedSourcePos = i + j;
                                        }
                                        if (s [i + j] != target [j]) {
                                                no = true;
                                                break;
                                        }
                                }
                                if (no)
                                        continue;
                                return i;
                        }
                        return -1;
                }

                public unsafe int IndexOf (string s, string target, int start, int length, CompareOptions opt)
                {
                        if (opt == CompareOptions.Ordinal)
                                return IndexOfOrdinal (s, target, start, length);
                        if (opt == CompareOptions.OrdinalIgnoreCase)
                                return IndexOfOrdinalIgnoreCase (s, target, start, length);
                        if (opt == CompareOptions.None) {
                                bool testWasUnable;
                                int ret = QuickIndexOf (s, target, start, length, out testWasUnable);
                                if (!testWasUnable)
                                        return ret;
                        }

                        byte* alwaysMatchFlags = stackalloc byte [16];
                        byte* neverMatchFlags = stackalloc byte [16];
                        byte* targetSortKey = stackalloc byte [4];
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (alwaysMatchFlags, 16);
                        ClearBuffer (neverMatchFlags, 16);
                        ClearBuffer (targetSortKey, 4);
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        Context ctx = new Context (opt, alwaysMatchFlags, neverMatchFlags, sk1, sk2, null, false);

                        return IndexOf (s, target, start, length,
                                targetSortKey, ref ctx);
                }

                // note that it wouldn't be used since ordinal IndexOf()
                // should be directed to icall.
                int IndexOfOrdinal (string s, string target, int start, int length)
                {
                        if (target.Length == 0)
                                return 0;
                        else if (target.Length > length)
                                return -1;

                        int end = start + length - target.Length + 1;
                        for (int i = start; i < end; i++) {
                                bool no = false;
                                for (int j = 0; j < target.Length; j++) {
                                        if (s [i + j] != target [j]) {
                                                no = true;
                                                break;
                                        }
                                }
                                if (no)
                                        continue;
                                return i;
                        }
                        return -1;
                }

                int IndexOfOrdinalIgnoreCase (string s, string target, int start, int length)
                {
                        if (target.Length == 0)
                                return 0;
                        else if (target.Length > length)
                                return -1;

                        int end = start + length - target.Length + 1;
                        for (int i = start; i < end; i++) {
                                bool no = false;
                                for (int j = 0; j < target.Length; j++) {
                                        // I think almost all text has more lower letters than upper ones. Thus with this invariant comparison ToLower() should be faster since it costs less operations.
                                        if (textInfo.ToLower (s [i + j]) != textInfo.ToLower (target [j])) {
                                                no = true;
                                                break;
                                        }
                                }
                                if (no)
                                        continue;
                                return i;
                        }
                        return -1;
                }

                // char

                public int IndexOf (string s, char target, CompareOptions opt)
                {
                        return IndexOf (s, target, 0, s.Length, opt);
                }

                public unsafe int IndexOf (string s, char target, int start, int length, CompareOptions opt)
                {
                        if (opt == CompareOptions.Ordinal)
                                return IndexOfOrdinal (s, target, start, length);
                        if (opt == CompareOptions.OrdinalIgnoreCase)
                                return IndexOfOrdinalIgnoreCase (s, target, start, length);
                        byte* alwaysMatchFlags = stackalloc byte [16];
                        byte* neverMatchFlags = stackalloc byte [16];
                        byte* targetSortKey = stackalloc byte [4];
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (alwaysMatchFlags, 16);
                        ClearBuffer (neverMatchFlags, 16);
                        ClearBuffer (targetSortKey, 4);
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        Context ctx = new Context (opt, alwaysMatchFlags, neverMatchFlags, sk1, sk2, null, false);

                        // If target is contraction, then use string search.
                        Contraction ct = GetContraction (target);
                        if (ct != null) {
                                if (ct.Replacement != null)
                                        return IndexOf (s, ct.Replacement,
                                                start, length, targetSortKey, ref ctx);
                                else {
                                        for (int i = 0; i < ct.SortKey.Length; i++)
                                                sk2 [i] = ct.SortKey [i];
                                        return IndexOfSortKey (s, start, length, sk2, char.MinValue, -1, true, ref ctx);
                                }
                        } else {
                                int ti = FilterOptions ((int) target, opt);
                                targetSortKey [0] = Category (ti);
                                targetSortKey [1] = Level1 (ti);
                                if ((opt & COpt.IgnoreNonSpace) == 0)
                                        targetSortKey [2] =
                                                Level2 (ti, ExtenderType.None);
                                targetSortKey [3] = Uni.Level3 (ti);
                                return IndexOfSortKey (s, start, length,
                                        targetSortKey, target, ti,
                                        !Uni.HasSpecialWeight ((char) ti), ref ctx);
                        }
                }

                // note that it wouldn't be used since ordinal IndexOf()
                // should be directed to icall.
                int IndexOfOrdinal (string s, char target, int start, int length)
                {
                        int end = start + length;
                        for (int i = start; i < end; i++)
                                if (s [i] == target)
                                        return i;
                        return -1;
                }

                int IndexOfOrdinalIgnoreCase (string s, char target, int start, int length)
                {
                        int end = start + length;
                        target = textInfo.ToLower (target);
                        for (int i = start; i < end; i++)
                                if (textInfo.ToLower (s [i]) == target)
                                        return i;
                        return -1;
                }

                // Searches target byte[] keydata
                unsafe int IndexOfSortKey (string s, int start, int length, byte* sortkey, char target, int ti, bool noLv4, ref Context ctx)
                {
                        int end = start + length;
                        int idx = start;

                        while (idx < end) {
                                int cur = idx;
                                if (MatchesForward (s, ref idx, end, ti, sortkey, noLv4, ref ctx))
                                        return cur;
                        }
                        return -1;
                }

                // Searches string. Search head character (or keydata when
                // the head is contraction sortkey) and try IsPrefix().
                unsafe int IndexOf (string s, string target, int start, int length, byte* targetSortKey, ref Context ctx)
                {
                        COpt opt = ctx.Option;
                        int tidx = 0;
                        for (; tidx < target.Length; tidx++)
                                if (!IsIgnorable (target [tidx], opt))
                                        break;
                        if (tidx == target.Length)
                                return start;
                        Contraction ct = GetContraction (target, tidx, target.Length - tidx);
                        string replace = ct != null ? ct.Replacement : null;
                        byte* sk = replace == null ? targetSortKey : null;
                        bool noLv4 = true;
                        char tc = char.MinValue;
                        int ti = -1;
                        if (ct != null && sk != null) {
                                for (int i = 0; i < ct.SortKey.Length; i++)
                                        sk [i] = ct.SortKey [i];
                        } else if (sk != null) {
                                tc = target [tidx];
                                ti = FilterOptions (target [tidx], opt);
                                sk [0] = Category (ti);
                                sk [1] = Level1 (ti);
                                if ((opt & COpt.IgnoreNonSpace) == 0)
                                        sk [2] = Level2 (ti, ExtenderType.None);
                                sk [3] = Uni.Level3 (ti);
                                noLv4 = !Uni.HasSpecialWeight ((char) ti);
                        }
                        if (sk != null) {
                                for (tidx++; tidx < target.Length; tidx++) {
                                        if (Category (target [tidx]) != 1)
                                                break;
                                        if (sk [2] == 0)
                                                sk [2] = 2;
                                        sk [2] = (byte) (sk [2] + Level2 (target [tidx], ExtenderType.None));
                                }
                        }

                        do {
                                int idx = 0;
                                if (replace != null)
                                        idx = IndexOf (s, replace, start, length, targetSortKey, ref ctx);
                                else
                                        idx = IndexOfSortKey (s, start, length, sk, tc, ti, noLv4, ref ctx);
                                if (idx < 0)
                                        return -1;
                                length -= idx - start;
                                start = idx;
                                if (IsPrefix (s, target, start, length, false, ref ctx))
                                        return idx;
                                Contraction cts = GetContraction (s, start, length);
                                if (cts != null) {
                                        start += cts.Source.Length;
                                        length -= cts.Source.Length;
                                } else {
                                        start++;
                                        length--;
                                }
                        } while (length > 0);
                        return -1;
                }

                //
                // There are the same number of LastIndexOf() methods as
                // IndexOf() related methods, with the same functionalities
                // for each.
                //

                // string

                public int LastIndexOf (string s, string target, CompareOptions opt)
                {
                        return LastIndexOf (s, target, s.Length - 1, s.Length, opt);
                }

                public unsafe int LastIndexOf (string s, string target, int start, int length, CompareOptions opt)
                {
                        if (opt == CompareOptions.Ordinal)
                                return LastIndexOfOrdinal (s, target, start, length);
                        if (opt == CompareOptions.OrdinalIgnoreCase)
                                return LastIndexOfOrdinalIgnoreCase (s, target, start, length);
                        byte* alwaysMatchFlags = stackalloc byte [16];
                        byte* neverMatchFlags = stackalloc byte [16];
                        byte* targetSortKey = stackalloc byte [4];
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (alwaysMatchFlags, 16);
                        ClearBuffer (neverMatchFlags, 16);
                        ClearBuffer (targetSortKey, 4);
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        // For some unknown reason CompareQuick() does not work fine w/ LastIndexOf().
                        Context ctx = new Context (opt, alwaysMatchFlags, neverMatchFlags, sk1, sk2, null, false);
                        return LastIndexOf (s, target, start, length,
                                targetSortKey, ref ctx);
                }

                int LastIndexOfOrdinal (string s, string target, int start, int length)
                {
                        if (target.Length == 0)
                                return 0;
                        if (s.Length < target.Length || target.Length > length)
                                return -1;
                        int end = start - length + target.Length -1;
                        char tail = target [target.Length - 1];
                        for (int i = start; i > end;) {
                                if (s [i] != tail) {
                                        i--;
                                        continue;
                                }
                                int x = i - target.Length + 1;
                                i--;
                                bool mismatch = false;
                                for (int j = target.Length - 2; j >= 0; j--)
                                        if (s [x + j] != target [j]) {
                                                mismatch = true;
                                                break;
                                        }
                                if (mismatch)
                                        continue;
                                return x;
                        }
                        return -1;
                }

                int LastIndexOfOrdinalIgnoreCase (string s, string target, int start, int length)
                {
                        if (target.Length == 0)
                                return 0;
                        if (s.Length < length || target.Length > length)
                                return -1;
                        int end = start - length + target.Length - 1;
                        char tail = textInfo.ToLower (target [target.Length - 1]);
                        for (int i = start; i > end;) {
                                if (textInfo.ToLower (s [i]) != tail) {
                                        i--;
                                        continue;
                                }
                                int x = i - target.Length + 1;
                                i--;
                                bool mismatch = false;
                                for (int j = target.Length - 2; j >= 0; j--)
                                        if (textInfo.ToLower (s [x + j]) != textInfo.ToLower (target [j])) {
                                                mismatch = true;
                                                break;
                                        }
                                if (mismatch)
                                        continue;
                                return x;
                        }
                        return -1;
                }

                // char

                public int LastIndexOf (string s, char target, CompareOptions opt)
                {
                        return LastIndexOf (s, target, s.Length - 1, s.Length, opt);
                }

                public unsafe int LastIndexOf (string s, char target, int start, int length, CompareOptions opt)
                {
                        if (opt == CompareOptions.Ordinal)
                                return LastIndexOfOrdinal (s, target, start, length);
                        if (opt == CompareOptions.OrdinalIgnoreCase)
                                return LastIndexOfOrdinalIgnoreCase (s, target, start, length);
                        byte* alwaysMatchFlags = stackalloc byte [16];
                        byte* neverMatchFlags = stackalloc byte [16];
                        byte* targetSortKey = stackalloc byte [4];
                        byte* sk1 = stackalloc byte [4];
                        byte* sk2 = stackalloc byte [4];
                        ClearBuffer (alwaysMatchFlags, 16);
                        ClearBuffer (neverMatchFlags, 16);
                        ClearBuffer (targetSortKey, 4);
                        ClearBuffer (sk1, 4);
                        ClearBuffer (sk2, 4);
                        Context ctx = new Context (opt, alwaysMatchFlags, neverMatchFlags, sk1, sk2, null, false);

                        // If target is a replacement contraction, then use 
                        // string search.
                        Contraction ct = GetContraction (target);
                        if (ct != null) {
                                if (ct.Replacement != null)
                                        return LastIndexOf (s,
                                                ct.Replacement, start, length,
                                                targetSortKey, ref ctx);
                                else {
                                        for (int bi = 0; bi < ct.SortKey.Length; bi++)
                                                sk2 [bi] = ct.SortKey [bi];
                                        return LastIndexOfSortKey (s, start,
                                                start, length, sk2,
                                                -1, true, ref ctx);
                                }
                        }
                        else {
                                int ti = FilterOptions ((int) target, opt);
                                targetSortKey [0] = Category (ti);
                                targetSortKey [1] = Level1 (ti);
                                if ((opt & COpt.IgnoreNonSpace) == 0)
                                        targetSortKey [2] = Level2 (ti, ExtenderType.None);
                                targetSortKey [3] = Uni.Level3 (ti);
                                return LastIndexOfSortKey (s, start, start,
                                        length, targetSortKey,
                                        ti, !Uni.HasSpecialWeight ((char) ti),
                                        ref ctx);
                        }
                }

                int LastIndexOfOrdinal (string s, char target, int start, int length)
                {
                        if (s.Length == 0)
                                return -1;
                        int end = start - length;
                        for (int i = start; i > end; i--)
                                if (s [i] == target)
                                        return i;
                        return -1;
                }

                int LastIndexOfOrdinalIgnoreCase (string s, char target, int start, int length)
                {
                        if (s.Length == 0)
                                return -1;
                        int end = start - length;
                        char c = textInfo.ToUpper (target);
                        for (int i = start; i > end; i--)
                                if (textInfo.ToUpper (s [i]) == c)
                                        return i;
                        return -1;
                }

                // Searches target byte[] keydata
                unsafe int LastIndexOfSortKey (string s, int start, int orgStart, int length, byte* sortkey, int ti, bool noLv4, ref Context ctx)
                {
                        int end = start - length;
                        int idx = start;
                        while (idx > end) {
                                int cur = idx;
                                if (MatchesBackward (s, ref idx, end, orgStart,
                                        ti, sortkey, noLv4, ref ctx))
                                        return cur;
                        }
                        return -1;
                }

                // Searches string. Search head character (or keydata when
                // the head is contraction sortkey) and try IsPrefix().
                unsafe int LastIndexOf (string s, string target, int start, int length, byte* targetSortKey, ref Context ctx)
                {
                        COpt opt = ctx.Option;
                        int orgStart = start;
                        int tidx = 0;
                        for (; tidx < target.Length; tidx++)
                                if (!IsIgnorable (target [tidx], opt))
                                        break;
                        if (tidx == target.Length)
                                return start;
                        Contraction ct = GetContraction (target, tidx, target.Length - tidx);
                        string replace = ct != null ? ct.Replacement : null;
                        byte* sk = replace == null ? targetSortKey : null;

                        bool noLv4 = true;
                        int ti = -1;
                        if (ct != null && sk != null) {
                                for (int i = 0; i < ct.SortKey.Length; i++)
                                        sk [i] = ct.SortKey [i];
                        } else if (sk != null) {
                                ti = FilterOptions (target [tidx], opt);
                                sk [0] = Category (ti);
                                sk [1] = Level1 (ti);
                                if ((opt & COpt.IgnoreNonSpace) == 0)
                                        sk [2] = Level2 (ti, ExtenderType.None);
                                sk [3] = Uni.Level3 (ti);
                                noLv4 = !Uni.HasSpecialWeight ((char) ti);
                        }
                        if (sk != null) {
                                for (tidx++; tidx < target.Length; tidx++) {
                                        if (Category (target [tidx]) != 1)
                                                break;
                                        if (sk [2] == 0)
                                                sk [2] = 2;
                                        sk [2] = (byte) (sk [2] + Level2 (target [tidx], ExtenderType.None));
                                }
                        }

                        do {
                                int idx = 0;

                                if (replace != null)
                                        idx = LastIndexOf (s, replace,
                                                start, length,
                                                targetSortKey, ref ctx);
                                else
                                        idx = LastIndexOfSortKey (s, start, orgStart, length, sk, ti, noLv4, ref ctx);
                                if (idx < 0)
                                        return -1;
                                length -= start - idx;
                                start = idx;

                                if (IsPrefix (s, target, idx, orgStart - idx + 1, false, ref ctx)) {
                                        for (;idx < orgStart; idx++)
                                                if (!IsIgnorable (s [idx], opt))
                                                        break;
                                        return idx;
                                }
                                Contraction cts = GetContraction (s, idx, orgStart - idx + 1);
                                if (cts != null) {
                                        start -= cts.Source.Length;
                                        length -= cts.Source.Length;
                                } else {
                                        start--;
                                        length--;
                                }
                        } while (length > 0);
                        return -1;
                }

                unsafe bool MatchesForward (string s, ref int idx, int end, int ti, byte* sortkey, bool noLv4, ref Context ctx)
                {
                        int si = s [idx];
                        if (ctx.AlwaysMatchFlags != null && si < 128 && (ctx.AlwaysMatchFlags [si / 8] & (1 << (si % 8))) != 0)
                                return true;
                        if (ctx.NeverMatchFlags != null &&
                                        si < 128 &&
                                        (ctx.NeverMatchFlags [si / 8] & (1 << (si % 8))) != 0) {
                                idx++;
                                return false;
                        }
                        ExtenderType ext = GetExtenderType (s [idx]);
                        Contraction ct = null;
                        if (MatchesForwardCore (s, ref idx, end, ti, sortkey, noLv4, ext, ref ct, ref ctx)) {
                                if (ctx.AlwaysMatchFlags != null && ct == null && ext == ExtenderType.None && si < 128)
                                        ctx.AlwaysMatchFlags [si / 8] |= (byte) (1 << (si % 8));
                                return true;
                        }
                        if (ctx.NeverMatchFlags != null && ct == null && ext == ExtenderType.None && si < 128)
                                ctx.NeverMatchFlags [si / 8] |= (byte) (1 << (si % 8));
                        return false;
                }

                unsafe bool MatchesForwardCore (string s, ref int idx, int end, int ti, byte* sortkey, bool noLv4, ExtenderType ext, ref Contraction ct, ref Context ctx)
                {
                        COpt opt = ctx.Option;
                        byte* charSortKey = ctx.Buffer1;
                        bool ignoreNonSpace = (opt & COpt.IgnoreNonSpace) != 0;
                        int si = -1;
                        if (ext == ExtenderType.None)
                                ct = GetContraction (s, idx, end);
                        else if (ctx.PrevCode < 0) {
                                if (ctx.PrevSortKey == null) {
                                        idx++;
                                        return false;
                                }
                                charSortKey = ctx.PrevSortKey;
                        }
                        else
                                si = FilterExtender (ctx.PrevCode, ext, opt);
                        // if lv4 exists, it never matches contraction
                        if (ct != null) {
                                idx += ct.Source.Length;
                                if (!noLv4)
                                        return false;
                                if (ct.SortKey != null) {
                                        for (int i = 0; i < 4; i++)
                                                charSortKey [i] = sortkey [i];
                                        ctx.PrevCode = -1;
                                        ctx.PrevSortKey = charSortKey;
                                } else {
                                        // Here is the core of LAMESPEC
                                        // described at the top of the source.
                                        int dummy = 0;
                                        return MatchesForward (ct.Replacement, ref dummy,
                                                ct.Replacement.Length, ti, sortkey, noLv4, ref ctx);
                                }
                        } else {
                                if (si < 0)
                                        si = FilterOptions (s [idx], opt);
                                idx++;
                                charSortKey [0] = Category (si);
                                bool noMatch = false;
                                if (sortkey [0] == charSortKey [0])
                                        charSortKey [1] = Level1 (si);
                                else
                                        noMatch = true;
                                if (!ignoreNonSpace && sortkey [1] == charSortKey [1])
                                        charSortKey [2] = Level2 (si, ext);
                                else if (!ignoreNonSpace)
                                        noMatch = true;
                                if (noMatch) {
                                        for (; idx < end; idx++) {
                                                if (Category (s [idx]) != 1)
                                                        break;
                                        }
                                        return false;
                                }
                                charSortKey [3] = Uni.Level3 (si);
                                if (charSortKey [0] != 1)
                                        ctx.PrevCode = si;
                        }
                        for (; idx < end; idx++) {
                                if (Category (s [idx]) != 1)
                                        break;
                                if (ignoreNonSpace)
                                        continue;
                                if (charSortKey [2] == 0)
                                                charSortKey [2] = 2;
                                        charSortKey [2] = (byte) (charSortKey [2]
                                                + Level2 (s [idx], ExtenderType.None));
                        }

                        return MatchesPrimitive (opt, charSortKey, si, ext, sortkey, ti, noLv4);
                }

                unsafe bool MatchesPrimitive (COpt opt, byte* source, int si, ExtenderType ext, byte* target, int ti, bool noLv4)
                {
                        bool ignoreNonSpace = (opt & COpt.IgnoreNonSpace) != 0;
                        if (source [0] != target [0] ||
                                source [1] != target [1] ||
                                (!ignoreNonSpace && source [2] != target [2]) ||
                                source [3] != target [3])
                                return false;
                        if (noLv4 && (si < 0 || !Uni.HasSpecialWeight ((char) si)))
                                return true;
                        else if (noLv4)
                                return false;
                        // Since target can never be an extender, if the source
                        // is an expander and it matters, then they never match.
                        if (!ignoreNonSpace && ext == ExtenderType.Conditional)
                                return false;
                        if (Uni.IsJapaneseSmallLetter ((char) si) !=
                                Uni.IsJapaneseSmallLetter ((char) ti) ||
                                ToDashTypeValue (ext, opt) !=
                                // FIXME: we will have to specify correct value for target
                                ToDashTypeValue (ExtenderType.None, opt) ||
                                !Uni.IsHiragana ((char) si) !=
                                !Uni.IsHiragana ((char) ti) ||
                                IsHalfKana ((char) si, opt) !=
                                IsHalfKana ((char) ti, opt))
                                return false;
                        return true;
                }

                unsafe bool MatchesBackward (string s, ref int idx, int end, int orgStart, int ti, byte* sortkey, bool noLv4, ref Context ctx)
                {
                        int si = s [idx];
                        if (ctx.AlwaysMatchFlags != null && si < 128 && (ctx.AlwaysMatchFlags [si / 8] & (1 << (si % 8))) != 0)
                                return true;
                        if (ctx.NeverMatchFlags != null && si < 128 && (ctx.NeverMatchFlags [si / 8] & (1 << (si % 8))) != 0) {
                                idx--;
                                return false;
                        }
                        ExtenderType ext = GetExtenderType (s [idx]);
                        Contraction ct = null;
                        if (MatchesBackwardCore (s, ref idx, end, orgStart, ti, sortkey, noLv4, ext, ref ct, ref ctx)) {
                                if (ctx.AlwaysMatchFlags != null && ct == null && ext == ExtenderType.None && si < 128)
                                        ctx.AlwaysMatchFlags [si / 8] |= (byte) (1 << (si % 8));
                                return true;
                        }
                        if (ctx.NeverMatchFlags != null && ct == null && ext == ExtenderType.None && si < 128) {
                                ctx.NeverMatchFlags [si / 8] |= (byte) (1 << (si % 8));
                        }
                        return false;
                }

                unsafe bool MatchesBackwardCore (string s, ref int idx, int end, int orgStart, int ti, byte* sortkey, bool noLv4, ExtenderType ext, ref Contraction ct, ref Context ctx)
                {
                        COpt opt = ctx.Option;
                        byte* charSortKey = ctx.Buffer1;
                        bool ignoreNonSpace = (opt & COpt.IgnoreNonSpace) != 0;
                        int cur = idx;
                        int si = -1;
                        // To handle extenders in source, we need to
                        // check next _primary_ character.
                        if (ext != ExtenderType.None) {
                                byte diacritical = 0;
                                for (int tmp = 0; ; tmp--) {
                                        if (tmp < 0) // heading extender
                                                return false;
                                        if (IsIgnorable (s [tmp], opt))
                                                continue;
                                        int tmpi = FilterOptions (s [tmp], opt);
                                        byte category = Category (tmpi);
                                        if (category == 1) {
                                                diacritical = Level2 (tmpi, ExtenderType.None);
                                                continue;
                                        }
                                        si = FilterExtender (tmpi, ext, opt);
                                        charSortKey [0] = category;
                                        charSortKey [1] = Level1 (si);
                                        if (!ignoreNonSpace)
                                                charSortKey [2] = Level2 (si, ext);
                                        charSortKey [3] = Uni.Level3 (si);
                                        if (ext != ExtenderType.Conditional &&
                                                diacritical != 0)
                                                charSortKey [2] =
                                                        (charSortKey [2] == 0) ?
                                                        (byte) (diacritical + 2) :
                                                        diacritical;
                                        break;
                                }
                                idx--;
                        }
                        if (ext == ExtenderType.None)
                                ct = GetTailContraction (s, idx, end);
                        // if lv4 exists, it never matches contraction
                        if (ct != null) {
                                idx -= ct.Source.Length;
                                if (!noLv4)
                                        return false;
                                if (ct.SortKey != null) {
                                        for (int i = 0; i < 4; i++)
                                                charSortKey [i] = sortkey [i];
                                        ctx.PrevCode = -1;
                                        ctx.PrevSortKey = charSortKey;
                                } else {
                                        // Here is the core of LAMESPEC
                                        // described at the top of the source.
                                        int dummy = ct.Replacement.Length - 1;
                                        return 0 <= LastIndexOfSortKey (
                                                ct.Replacement, dummy, dummy,
                                                ct.Replacement.Length, sortkey,
                                                ti, noLv4, ref ctx);
                                }
                        } else if (ext == ExtenderType.None) {
                                if (si < 0)
                                        si = FilterOptions (s [idx], opt);
                                idx--;
                                bool noMatch = false;
                                charSortKey [0] = Category (si);
                                if (charSortKey [0] == sortkey [0])
                                        charSortKey [1] = Level1 (si);
                                else
                                        noMatch = true;
                                if (!ignoreNonSpace && charSortKey [1] == sortkey [1])
                                        charSortKey [2] = Level2 (si, ext);
                                else if (!ignoreNonSpace)
                                        noMatch = true;
                                if (noMatch)
                                        return false;
                                charSortKey [3] = Uni.Level3 (si);
                                if (charSortKey [0] != 1)
                                        ctx.PrevCode = si;
                        }
                        if (ext == ExtenderType.None) {
                                for (int tmp = cur + 1; tmp < orgStart; tmp++) {
                                        if (Category (s [tmp]) != 1)
                                                break;
                                        if (ignoreNonSpace)
                                                continue;
                                        if (charSortKey [2] == 0)
                                                        charSortKey [2] = 2;
                                        charSortKey [2] = (byte) (charSortKey [2]
                                                + Level2 (s [tmp], ExtenderType.None));
                                }
                        }
                        return MatchesPrimitive (opt, charSortKey, si, ext, sortkey, ti, noLv4);
                }
                #endregion
        }
}