doc PG 17 relnotes: add FETCH_COUNT item

[pgsql.git] / src / common / unicode_norm.c

/*-------------------------------------------------------------------------
 * unicode_norm.c
 *              Normalize a Unicode string
 *
 * This implements Unicode normalization, per the documentation at
 * https://www.unicode.org/reports/tr15/.
 *
 * Portions Copyright (c) 2017-2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *        src/common/unicode_norm.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include "common/unicode_norm.h"
#ifndef FRONTEND
#include "common/unicode_norm_hashfunc.h"
#include "common/unicode_normprops_table.h"
#include "port/pg_bswap.h"
#else
#include "common/unicode_norm_table.h"
#endif

#ifndef FRONTEND
#define ALLOC(size) palloc(size)
#define FREE(size) pfree(size)
#else
#define ALLOC(size) malloc(size)
#define FREE(size) free(size)
#endif

/* Constants for calculations with Hangul characters */
#define SBASE           0xAC00          /* U+AC00 */
#define LBASE           0x1100          /* U+1100 */
#define VBASE           0x1161          /* U+1161 */
#define TBASE           0x11A7          /* U+11A7 */
#define LCOUNT          19
#define VCOUNT          21
#define TCOUNT          28
#define NCOUNT          VCOUNT * TCOUNT
#define SCOUNT          LCOUNT * NCOUNT

#ifdef FRONTEND
/* comparison routine for bsearch() of decomposition lookup table. */
static int
conv_compare(const void *p1, const void *p2)
{
        uint32          v1,
                                v2;

        v1 = *(const uint32 *) p1;
        v2 = ((const pg_unicode_decomposition *) p2)->codepoint;
        return (v1 > v2) ? 1 : ((v1 == v2) ? 0 : -1);
}

#endif

/*
 * get_code_entry
 *
 * Get the entry corresponding to code in the decomposition lookup table.
 * The backend version of this code uses a perfect hash function for the
 * lookup, while the frontend version uses a binary search.
 */
static const pg_unicode_decomposition *
get_code_entry(pg_wchar code)
{
#ifndef FRONTEND
        int                     h;
        uint32          hashkey;
        pg_unicode_decompinfo decompinfo = UnicodeDecompInfo;

        /*
         * Compute the hash function. The hash key is the codepoint with the bytes
         * in network order.
         */
        hashkey = pg_hton32(code);
        h = decompinfo.hash(&hashkey);

        /* An out-of-range result implies no match */
        if (h < 0 || h >= decompinfo.num_decomps)
                return NULL;

        /*
         * Since it's a perfect hash, we need only match to the specific codepoint
         * it identifies.
         */
        if (code != decompinfo.decomps[h].codepoint)
                return NULL;

        /* Success! */
        return &decompinfo.decomps[h];
#else
        return bsearch(&(code),
                                   UnicodeDecompMain,
                                   lengthof(UnicodeDecompMain),
                                   sizeof(pg_unicode_decomposition),
                                   conv_compare);
#endif
}

/*
 * Get the combining class of the given codepoint.
 */
static uint8
get_canonical_class(pg_wchar code)
{
        const pg_unicode_decomposition *entry = get_code_entry(code);

        /*
         * If no entries are found, the character used is either an Hangul
         * character or a character with a class of 0 and no decompositions.
         */
        if (!entry)
                return 0;
        else
                return entry->comb_class;
}

/*
 * Given a decomposition entry looked up earlier, get the decomposed
 * characters.
 *
 * Note: the returned pointer can point to statically allocated buffer, and
 * is only valid until next call to this function!
 */
static const pg_wchar *
get_code_decomposition(const pg_unicode_decomposition *entry, int *dec_size)
{
        static pg_wchar x;

        if (DECOMPOSITION_IS_INLINE(entry))
        {
                Assert(DECOMPOSITION_SIZE(entry) == 1);
                x = (pg_wchar) entry->dec_index;
                *dec_size = 1;
                return &x;
        }
        else
        {
                *dec_size = DECOMPOSITION_SIZE(entry);
                return &UnicodeDecomp_codepoints[entry->dec_index];
        }
}

/*
 * Calculate how many characters a given character will decompose to.
 *
 * This needs to recurse, if the character decomposes into characters that
 * are, in turn, decomposable.
 */
static int
get_decomposed_size(pg_wchar code, bool compat)
{
        const pg_unicode_decomposition *entry;
        int                     size = 0;
        int                     i;
        const uint32 *decomp;
        int                     dec_size;

        /*
         * Fast path for Hangul characters not stored in tables to save memory as
         * decomposition is algorithmic. See
         * https://www.unicode.org/reports/tr15/tr15-18.html, annex 10 for details
         * on the matter.
         */
        if (code >= SBASE && code < SBASE + SCOUNT)
        {
                uint32          tindex,
                                        sindex;

                sindex = code - SBASE;
                tindex = sindex % TCOUNT;

                if (tindex != 0)
                        return 3;
                return 2;
        }

        entry = get_code_entry(code);

        /*
         * Just count current code if no other decompositions.  A NULL entry is
         * equivalent to a character with class 0 and no decompositions.
         */
        if (entry == NULL || DECOMPOSITION_SIZE(entry) == 0 ||
                (!compat && DECOMPOSITION_IS_COMPAT(entry)))
                return 1;

        /*
         * If this entry has other decomposition codes look at them as well. First
         * get its decomposition in the list of tables available.
         */
        decomp = get_code_decomposition(entry, &dec_size);
        for (i = 0; i < dec_size; i++)
        {
                uint32          lcode = decomp[i];

                size += get_decomposed_size(lcode, compat);
        }

        return size;
}

/*
 * Recompose a set of characters. For hangul characters, the calculation
 * is algorithmic. For others, an inverse lookup at the decomposition
 * table is necessary. Returns true if a recomposition can be done, and
 * false otherwise.
 */
static bool
recompose_code(uint32 start, uint32 code, uint32 *result)
{
        /*
         * Handle Hangul characters algorithmically, per the Unicode spec.
         *
         * Check if two current characters are L and V.
         */
        if (start >= LBASE && start < LBASE + LCOUNT &&
                code >= VBASE && code < VBASE + VCOUNT)
        {
                /* make syllable of form LV */
                uint32          lindex = start - LBASE;
                uint32          vindex = code - VBASE;

                *result = SBASE + (lindex * VCOUNT + vindex) * TCOUNT;
                return true;
        }
        /* Check if two current characters are LV and T */
        else if (start >= SBASE && start < (SBASE + SCOUNT) &&
                         ((start - SBASE) % TCOUNT) == 0 &&
                         code >= TBASE && code < (TBASE + TCOUNT))
        {
                /* make syllable of form LVT */
                uint32          tindex = code - TBASE;

                *result = start + tindex;
                return true;
        }
        else
        {
                const pg_unicode_decomposition *entry;

                /*
                 * Do an inverse lookup of the decomposition tables to see if anything
                 * matches. The comparison just needs to be a perfect match on the
                 * sub-table of size two, because the start character has already been
                 * recomposed partially.  This lookup uses a perfect hash function for
                 * the backend code.
                 */
#ifndef FRONTEND

                int                     h,
                                        inv_lookup_index;
                uint64          hashkey;
                pg_unicode_recompinfo recompinfo = UnicodeRecompInfo;

                /*
                 * Compute the hash function. The hash key is formed by concatenating
                 * bytes of the two codepoints in network order. See also
                 * src/common/unicode/generate-unicode_norm_table.pl.
                 */
                hashkey = pg_hton64(((uint64) start << 32) | (uint64) code);
                h = recompinfo.hash(&hashkey);

                /* An out-of-range result implies no match */
                if (h < 0 || h >= recompinfo.num_recomps)
                        return false;

                inv_lookup_index = recompinfo.inverse_lookup[h];
                entry = &UnicodeDecompMain[inv_lookup_index];

                if (start == UnicodeDecomp_codepoints[entry->dec_index] &&
                        code == UnicodeDecomp_codepoints[entry->dec_index + 1])
                {
                        *result = entry->codepoint;
                        return true;
                }

#else

                int                     i;

                for (i = 0; i < lengthof(UnicodeDecompMain); i++)
                {
                        entry = &UnicodeDecompMain[i];

                        if (DECOMPOSITION_SIZE(entry) != 2)
                                continue;

                        if (DECOMPOSITION_NO_COMPOSE(entry))
                                continue;

                        if (start == UnicodeDecomp_codepoints[entry->dec_index] &&
                                code == UnicodeDecomp_codepoints[entry->dec_index + 1])
                        {
                                *result = entry->codepoint;
                                return true;
                        }
                }
#endif                                                  /* !FRONTEND */
        }

        return false;
}

/*
 * Decompose the given code into the array given by caller. The
 * decomposition begins at the position given by caller, saving one
 * lookup on the decomposition table. The current position needs to be
 * updated here to let the caller know from where to continue filling
 * in the array result.
 */
static void
decompose_code(pg_wchar code, bool compat, pg_wchar **result, int *current)
{
        const pg_unicode_decomposition *entry;
        int                     i;
        const uint32 *decomp;
        int                     dec_size;

        /*
         * Fast path for Hangul characters not stored in tables to save memory as
         * decomposition is algorithmic. See
         * https://www.unicode.org/reports/tr15/tr15-18.html, annex 10 for details
         * on the matter.
         */
        if (code >= SBASE && code < SBASE + SCOUNT)
        {
                uint32          l,
                                        v,
                                        tindex,
                                        sindex;
                pg_wchar   *res = *result;

                sindex = code - SBASE;
                l = LBASE + sindex / (VCOUNT * TCOUNT);
                v = VBASE + (sindex % (VCOUNT * TCOUNT)) / TCOUNT;
                tindex = sindex % TCOUNT;

                res[*current] = l;
                (*current)++;
                res[*current] = v;
                (*current)++;

                if (tindex != 0)
                {
                        res[*current] = TBASE + tindex;
                        (*current)++;
                }

                return;
        }

        entry = get_code_entry(code);

        /*
         * Just fill in with the current decomposition if there are no
         * decomposition codes to recurse to.  A NULL entry is equivalent to a
         * character with class 0 and no decompositions, so just leave also in
         * this case.
         */
        if (entry == NULL || DECOMPOSITION_SIZE(entry) == 0 ||
                (!compat && DECOMPOSITION_IS_COMPAT(entry)))
        {
                pg_wchar   *res = *result;

                res[*current] = code;
                (*current)++;
                return;
        }

        /*
         * If this entry has other decomposition codes look at them as well.
         */
        decomp = get_code_decomposition(entry, &dec_size);
        for (i = 0; i < dec_size; i++)
        {
                pg_wchar        lcode = (pg_wchar) decomp[i];

                /* Leave if no more decompositions */
                decompose_code(lcode, compat, result, current);
        }
}

/*
 * unicode_normalize - Normalize a Unicode string to the specified form.
 *
 * The input is a 0-terminated array of codepoints.
 *
 * In frontend, returns a 0-terminated array of codepoints, allocated with
 * malloc. Or NULL if we run out of memory. In backend, the returned
 * string is palloc'd instead, and OOM is reported with ereport().
 */
pg_wchar *
unicode_normalize(UnicodeNormalizationForm form, const pg_wchar *input)
{
        bool            compat = (form == UNICODE_NFKC || form == UNICODE_NFKD);
        bool            recompose = (form == UNICODE_NFC || form == UNICODE_NFKC);
        pg_wchar   *decomp_chars;
        pg_wchar   *recomp_chars;
        int                     decomp_size,
                                current_size;
        int                     count;
        const pg_wchar *p;

        /* variables for recomposition */
        int                     last_class;
        int                     starter_pos;
        int                     target_pos;
        uint32          starter_ch;

        /* First, do character decomposition */

        /*
         * Calculate how many characters long the decomposed version will be.
         */
        decomp_size = 0;
        for (p = input; *p; p++)
                decomp_size += get_decomposed_size(*p, compat);

        decomp_chars = (pg_wchar *) ALLOC((decomp_size + 1) * sizeof(pg_wchar));
        if (decomp_chars == NULL)
                return NULL;

        /*
         * Now fill in each entry recursively. This needs a second pass on the
         * decomposition table.
         */
        current_size = 0;
        for (p = input; *p; p++)
                decompose_code(*p, compat, &decomp_chars, &current_size);
        decomp_chars[decomp_size] = '\0';
        Assert(decomp_size == current_size);

        /* Leave if there is nothing to decompose */
        if (decomp_size == 0)
                return decomp_chars;

        /*
         * Now apply canonical ordering.
         */
        for (count = 1; count < decomp_size; count++)
        {
                pg_wchar        prev = decomp_chars[count - 1];
                pg_wchar        next = decomp_chars[count];
                pg_wchar        tmp;
                const uint8 prevClass = get_canonical_class(prev);
                const uint8 nextClass = get_canonical_class(next);

                /*
                 * Per Unicode (https://www.unicode.org/reports/tr15/tr15-18.html)
                 * annex 4, a sequence of two adjacent characters in a string is an
                 * exchangeable pair if the combining class (from the Unicode
                 * Character Database) for the first character is greater than the
                 * combining class for the second, and the second is not a starter.  A
                 * character is a starter if its combining class is 0.
                 */
                if (prevClass == 0 || nextClass == 0)
                        continue;

                if (prevClass <= nextClass)
                        continue;

                /* exchange can happen */
                tmp = decomp_chars[count - 1];
                decomp_chars[count - 1] = decomp_chars[count];
                decomp_chars[count] = tmp;

                /* backtrack to check again */
                if (count > 1)
                        count -= 2;
        }

        if (!recompose)
                return decomp_chars;

        /*
         * The last phase of NFC and NFKC is the recomposition of the reordered
         * Unicode string using combining classes. The recomposed string cannot be
         * longer than the decomposed one, so make the allocation of the output
         * string based on that assumption.
         */
        recomp_chars = (pg_wchar *) ALLOC((decomp_size + 1) * sizeof(pg_wchar));
        if (!recomp_chars)
        {
                FREE(decomp_chars);
                return NULL;
        }

        last_class = -1;                        /* this eliminates a special check */
        starter_pos = 0;
        target_pos = 1;
        starter_ch = recomp_chars[0] = decomp_chars[0];

        for (count = 1; count < decomp_size; count++)
        {
                pg_wchar        ch = decomp_chars[count];
                int                     ch_class = get_canonical_class(ch);
                pg_wchar        composite;

                if (last_class < ch_class &&
                        recompose_code(starter_ch, ch, &composite))
                {
                        recomp_chars[starter_pos] = composite;
                        starter_ch = composite;
                }
                else if (ch_class == 0)
                {
                        starter_pos = target_pos;
                        starter_ch = ch;
                        last_class = -1;
                        recomp_chars[target_pos++] = ch;
                }
                else
                {
                        last_class = ch_class;
                        recomp_chars[target_pos++] = ch;
                }
        }
        recomp_chars[target_pos] = (pg_wchar) '\0';

        FREE(decomp_chars);

        return recomp_chars;
}

/*
 * Normalization "quick check" algorithm; see
 * <http://www.unicode.org/reports/tr15/#Detecting_Normalization_Forms>
 */

/* We only need this in the backend. */
#ifndef FRONTEND

static const pg_unicode_normprops *
qc_hash_lookup(pg_wchar ch, const pg_unicode_norminfo *norminfo)
{
        int                     h;
        uint32          hashkey;

        /*
         * Compute the hash function. The hash key is the codepoint with the bytes
         * in network order.
         */
        hashkey = pg_hton32(ch);
        h = norminfo->hash(&hashkey);

        /* An out-of-range result implies no match */
        if (h < 0 || h >= norminfo->num_normprops)
                return NULL;

        /*
         * Since it's a perfect hash, we need only match to the specific codepoint
         * it identifies.
         */
        if (ch != norminfo->normprops[h].codepoint)
                return NULL;

        /* Success! */
        return &norminfo->normprops[h];
}

/*
 * Look up the normalization quick check character property
 */
static UnicodeNormalizationQC
qc_is_allowed(UnicodeNormalizationForm form, pg_wchar ch)
{
        const pg_unicode_normprops *found = NULL;

        switch (form)
        {
                case UNICODE_NFC:
                        found = qc_hash_lookup(ch, &UnicodeNormInfo_NFC_QC);
                        break;
                case UNICODE_NFKC:
                        found = qc_hash_lookup(ch, &UnicodeNormInfo_NFKC_QC);
                        break;
                default:
                        Assert(false);
                        break;
        }

        if (found)
                return found->quickcheck;
        else
                return UNICODE_NORM_QC_YES;
}

UnicodeNormalizationQC
unicode_is_normalized_quickcheck(UnicodeNormalizationForm form, const pg_wchar *input)
{
        uint8           lastCanonicalClass = 0;
        UnicodeNormalizationQC result = UNICODE_NORM_QC_YES;

        /*
         * For the "D" forms, we don't run the quickcheck.  We don't include the
         * lookup tables for those because they are huge, checking for these
         * particular forms is less common, and running the slow path is faster
         * for the "D" forms than the "C" forms because you don't need to
         * recompose, which is slow.
         */
        if (form == UNICODE_NFD || form == UNICODE_NFKD)
                return UNICODE_NORM_QC_MAYBE;

        for (const pg_wchar *p = input; *p; p++)
        {
                pg_wchar        ch = *p;
                uint8           canonicalClass;
                UnicodeNormalizationQC check;

                canonicalClass = get_canonical_class(ch);
                if (lastCanonicalClass > canonicalClass && canonicalClass != 0)
                        return UNICODE_NORM_QC_NO;

                check = qc_is_allowed(form, ch);
                if (check == UNICODE_NORM_QC_NO)
                        return UNICODE_NORM_QC_NO;
                else if (check == UNICODE_NORM_QC_MAYBE)
                        result = UNICODE_NORM_QC_MAYBE;

                lastCanonicalClass = canonicalClass;
        }
        return result;
}

#endif                                                  /* !FRONTEND */