dom/base/nsTextFragment.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * A class which represents a fragment of text (eg inside a text
   9  * node); if only codepoints below 256 are used, the text is stored as
  10  * a char*; otherwise the text is stored as a char16_t*
  11  */
  12
  13 #ifndef nsTextFragment_h___
  14 #define nsTextFragment_h___
  15
  16 #include "mozilla/Attributes.h"
  17 #include "mozilla/MemoryReporting.h"
  18
  19 #include "nsString.h"
  20 #include "nsStringBuffer.h"
  21 #include "nsReadableUtils.h"
  22 #include "nsISupportsImpl.h"
  23
  24 // XXX should this normalize the code to keep a \u0000 at the end?
  25
  26 // XXX nsTextFragmentPool?
  27
  28 /**
  29  * A fragment of text. If mIs2b is 1 then the m2b pointer is valid
  30  * otherwise the m1b pointer is valid. If m1b is used then each byte
  31  * of data represents a single ucs2 character with the high byte being
  32  * zero.
  33  *
  34  * This class does not have a virtual destructor therefore it is not
  35  * meant to be subclassed.
  36  */
  37 class nsTextFragment final {
  38  public:
  39   static nsresult Init();
  40   static void Shutdown();
  41
  42   /**
  43    * Default constructor. Initialize the fragment to be empty.
  44    */
  45   nsTextFragment() : m1b(nullptr), mAllBits(0) {
  46     MOZ_COUNT_CTOR(nsTextFragment);
  47     NS_ASSERTION(sizeof(FragmentBits) == 4, "Bad field packing!");
  48   }
  49
  50   ~nsTextFragment();
  51
  52   /**
  53    * Change the contents of this fragment to be a copy of the
  54    * the argument fragment, or to "" if unable to allocate enough memory.
  55    */
  56   nsTextFragment& operator=(const nsTextFragment& aOther);
  57
  58   /**
  59    * Return true if this fragment is represented by char16_t data
  60    */
  61   bool Is2b() const { return mState.mIs2b; }
  62
  63   /**
  64    * Return true if this fragment contains Bidi text
  65    * For performance reasons this flag is only set if explicitely requested (by
  66    * setting the aUpdateBidi argument on SetTo or Append to true).
  67    */
  68   bool IsBidi() const { return mState.mIsBidi; }
  69
  70   /**
  71    * Get a pointer to constant char16_t data.
  72    */
  73   const char16_t* Get2b() const {
  74     MOZ_ASSERT(Is2b(), "not 2b text");
  75     return static_cast<char16_t*>(m2b->Data());
  76   }
  77
  78   /**
  79    * Get a pointer to constant char data.
  80    */
  81   const char* Get1b() const {
  82     NS_ASSERTION(!Is2b(), "not 1b text");
  83     return (const char*)m1b;
  84   }
  85
  86   /**
  87    * Get the length of the fragment. The length is the number of logical
  88    * characters, not the number of bytes to store the characters.
  89    */
  90   uint32_t GetLength() const { return mState.mLength; }
  91
  92   bool CanGrowBy(size_t n) const {
  93     return n < (1 << 29) && mState.mLength + n < (1 << 29);
  94   }
  95
  96   /**
  97    * Change the contents of this fragment to be a copy of the given
  98    * buffer. If aUpdateBidi is true, contents of the fragment will be scanned,
  99    * and mState.mIsBidi will be turned on if it includes any Bidi characters.
 100    * If aForce2b is true, aBuffer will be stored as char16_t as is.  Then,
 101    * you can access the value faster but may waste memory if all characters
 102    * are less than U+0100.
 103    */
 104   bool SetTo(const char16_t* aBuffer, int32_t aLength, bool aUpdateBidi,
 105              bool aForce2b);
 106
 107   bool SetTo(const nsString& aString, bool aUpdateBidi, bool aForce2b) {
 108     ReleaseText();
 109     if (aForce2b && !aUpdateBidi) {
 110       nsStringBuffer* buffer = nsStringBuffer::FromString(aString);
 111       if (buffer) {
 112         NS_ADDREF(m2b = buffer);
 113         mState.mInHeap = true;
 114         mState.mIs2b = true;
 115         mState.mLength = aString.Length();
 116         return true;
 117       }
 118     }
 119
 120     return SetTo(aString.get(), aString.Length(), aUpdateBidi, aForce2b);
 121   }
 122
 123   /**
 124    * Append aData to the end of this fragment. If aUpdateBidi is true, contents
 125    * of the fragment will be scanned, and mState.mIsBidi will be turned on if
 126    * it includes any Bidi characters.
 127    * If aForce2b is true, the string will be stored as char16_t as is.  Then,
 128    * you can access the value faster but may waste memory if all characters
 129    * are less than U+0100.
 130    */
 131   bool Append(const char16_t* aBuffer, uint32_t aLength, bool aUpdateBidi,
 132               bool aForce2b);
 133
 134   /**
 135    * Append the contents of this string fragment to aString
 136    */
 137   void AppendTo(nsAString& aString) const {
 138     if (!AppendTo(aString, mozilla::fallible)) {
 139       aString.AllocFailed(aString.Length() + GetLength());
 140     }
 141   }
 142
 143   /**
 144    * Append the contents of this string fragment to aString
 145    * @return false if an out of memory condition is detected, true otherwise
 146    */
 147   MOZ_MUST_USE
 148   bool AppendTo(nsAString& aString,
 149                 const mozilla::fallible_t& aFallible) const {
 150     if (mState.mIs2b) {
 151       if (aString.IsEmpty()) {
 152         m2b->ToString(mState.mLength, aString);
 153         return true;
 154       }
 155       bool ok = aString.Append(Get2b(), mState.mLength, aFallible);
 156       if (!ok) {
 157         return false;
 158       }
 159
 160       return true;
 161     } else {
 162       return AppendASCIItoUTF16(Substring(m1b, mState.mLength), aString,
 163                                 aFallible);
 164     }
 165   }
 166
 167   /**
 168    * Append a substring of the contents of this string fragment to aString.
 169    * @param aOffset where to start the substring in this text fragment
 170    * @param aLength the length of the substring
 171    */
 172   void AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength) const {
 173     if (!AppendTo(aString, aOffset, aLength, mozilla::fallible)) {
 174       aString.AllocFailed(aString.Length() + aLength);
 175     }
 176   }
 177
 178   /**
 179    * Append a substring of the contents of this string fragment to aString.
 180    * @param aString the string in which to append
 181    * @param aOffset where to start the substring in this text fragment
 182    * @param aLength the length of the substring
 183    * @return false if an out of memory condition is detected, true otherwise
 184    */
 185   MOZ_MUST_USE
 186   bool AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength,
 187                 const mozilla::fallible_t& aFallible) const {
 188     if (mState.mIs2b) {
 189       bool ok = aString.Append(Get2b() + aOffset, aLength, aFallible);
 190       if (!ok) {
 191         return false;
 192       }
 193
 194       return true;
 195     } else {
 196       return AppendASCIItoUTF16(Substring(m1b + aOffset, aLength), aString,
 197                                 aFallible);
 198     }
 199   }
 200
 201   /**
 202    * Make a copy of the fragments contents starting at offset for
 203    * count characters. The offset and count will be adjusted to
 204    * lie within the fragments data. The fragments data is converted if
 205    * necessary.
 206    */
 207   void CopyTo(char16_t* aDest, int32_t aOffset, int32_t aCount);
 208
 209   /**
 210    * Return the character in the text-fragment at the given
 211    * index. This always returns a char16_t.
 212    */
 213   char16_t CharAt(int32_t aIndex) const {
 214     MOZ_ASSERT(uint32_t(aIndex) < mState.mLength, "bad index");
 215     return mState.mIs2b ? Get2b()[aIndex]
 216                         : static_cast<unsigned char>(m1b[aIndex]);
 217   }
 218
 219   void SetBidi(bool aBidi) { mState.mIsBidi = aBidi; }
 220
 221   struct FragmentBits {
 222     // uint32_t to ensure that the values are unsigned, because we
 223     // want 0/1, not 0/-1!
 224     // Making these bool causes Windows to not actually pack them,
 225     // which causes crashes because we assume this structure is no more than
 226     // 32 bits!
 227     uint32_t mInHeap : 1;
 228     uint32_t mIs2b : 1;
 229     uint32_t mIsBidi : 1;
 230     // Note that when you change the bits of mLength, you also need to change
 231     // NS_MAX_TEXT_FRAGMENT_LENGTH.
 232     uint32_t mLength : 29;
 233   };
 234
 235 #define NS_MAX_TEXT_FRAGMENT_LENGTH (static_cast<uint32_t>(0x1FFFFFFF))
 236
 237   size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
 238
 239   /**
 240    * Check whether the text in this fragment is the same as the text in the
 241    * other fragment.
 242    */
 243   MOZ_MUST_USE bool TextEquals(const nsTextFragment& aOther) const;
 244
 245  private:
 246   void ReleaseText();
 247
 248   /**
 249    * Scan the contents of the fragment and turn on mState.mIsBidi if it
 250    * includes any Bidi characters.
 251    */
 252   void UpdateBidiFlag(const char16_t* aBuffer, uint32_t aLength);
 253
 254   union {
 255     nsStringBuffer* m2b;
 256     const char* m1b;  // This is const since it can point to shared data
 257   };
 258
 259   union {
 260     uint32_t mAllBits;
 261     FragmentBits mState;
 262   };
 263 };
 264
 265 #endif /* nsTextFragment_h___ */