1 files changed, 317 insertions, 0 deletions
diff --git a/dom/base/nsTextFragment.h b/dom/base/nsTextFragment.h
new file mode 100644
index 0000000000..122dc619cb
--- /dev/null
+++ b/dom/base/nsTextFragment.h
@@ -0,0 +1,317 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * A class which represents a fragment of text (eg inside a text
+ * node); if only codepoints below 256 are used, the text is stored as
+ * a char*; otherwise the text is stored as a char16_t*
+ */
+
+#ifndef nsTextFragment_h___
+#define nsTextFragment_h___
+
+#include "mozilla/Attributes.h"
+#include "mozilla/MemoryReporting.h"
+
+#include "nsCharTraits.h"
+#include "nsString.h"
+#include "nsStringBuffer.h"
+#include "nsReadableUtils.h"
+#include "nsISupportsImpl.h"
+
+// XXX should this normalize the code to keep a \u0000 at the end?
+
+// XXX nsTextFragmentPool?
+
+/**
+ * A fragment of text. If mIs2b is 1 then the m2b pointer is valid
+ * otherwise the m1b pointer is valid. If m1b is used then each byte
+ * of data represents a single ucs2 character with the high byte being
+ * zero.
+ *
+ * This class does not have a virtual destructor therefore it is not
+ * meant to be subclassed.
+ */
+class nsTextFragment final {
+ public:
+  static nsresult Init();
+  static void Shutdown();
+
+  /**
+   * Default constructor. Initialize the fragment to be empty.
+   */
+  nsTextFragment() : m1b(nullptr), mAllBits(0) {
+    MOZ_COUNT_CTOR(nsTextFragment);
+    NS_ASSERTION(sizeof(FragmentBits) == 4, "Bad field packing!");
+  }
+
+  ~nsTextFragment();
+
+  /**
+   * Change the contents of this fragment to be a copy of the
+   * the argument fragment, or to "" if unable to allocate enough memory.
+   */
+  nsTextFragment& operator=(const nsTextFragment& aOther);
+
+  /**
+   * Return true if this fragment is represented by char16_t data
+   */
+  bool Is2b() const { return mState.mIs2b; }
+
+  /**
+   * Return true if this fragment contains Bidi text
+   * For performance reasons this flag is only set if explicitely requested (by
+   * setting the aUpdateBidi argument on SetTo or Append to true).
+   */
+  bool IsBidi() const { return mState.mIsBidi; }
+
+  /**
+   * Get a pointer to constant char16_t data.
+   */
+  const char16_t* Get2b() const {
+    MOZ_ASSERT(Is2b(), "not 2b text");
+    return static_cast<char16_t*>(m2b->Data());
+  }
+
+  /**
+   * Get a pointer to constant char data.
+   */
+  const char* Get1b() const {
+    NS_ASSERTION(!Is2b(), "not 1b text");
+    return (const char*)m1b;
+  }
+
+  /**
+   * Get the length of the fragment. The length is the number of logical
+   * characters, not the number of bytes to store the characters.
+   */
+  uint32_t GetLength() const { return mState.mLength; }
+
+  bool CanGrowBy(size_t n) const {
+    return n < (1 << 29) && mState.mLength + n < (1 << 29);
+  }
+
+  /**
+   * Change the contents of this fragment to be a copy of the given
+   * buffer. If aUpdateBidi is true, contents of the fragment will be scanned,
+   * and mState.mIsBidi will be turned on if it includes any Bidi characters.
+   * If aForce2b is true, aBuffer will be stored as char16_t as is.  Then,
+   * you can access the value faster but may waste memory if all characters
+   * are less than U+0100.
+   */
+  bool SetTo(const char16_t* aBuffer, int32_t aLength, bool aUpdateBidi,
+             bool aForce2b);
+
+  bool SetTo(const nsString& aString, bool aUpdateBidi, bool aForce2b) {
+    ReleaseText();
+    if (aForce2b && !aUpdateBidi) {
+      nsStringBuffer* buffer = nsStringBuffer::FromString(aString);
+      if (buffer) {
+        NS_ADDREF(m2b = buffer);
+        mState.mInHeap = true;
+        mState.mIs2b = true;
+        mState.mLength = aString.Length();
+        return true;
+      }
+    }
+
+    return SetTo(aString.get(), aString.Length(), aUpdateBidi, aForce2b);
+  }
+
+  /**
+   * Append aData to the end of this fragment. If aUpdateBidi is true, contents
+   * of the fragment will be scanned, and mState.mIsBidi will be turned on if
+   * it includes any Bidi characters.
+   * If aForce2b is true, the string will be stored as char16_t as is.  Then,
+   * you can access the value faster but may waste memory if all characters
+   * are less than U+0100.
+   */
+  bool Append(const char16_t* aBuffer, uint32_t aLength, bool aUpdateBidi,
+              bool aForce2b);
+
+  /**
+   * Append the contents of this string fragment to aString
+   */
+  void AppendTo(nsAString& aString) const {
+    if (!AppendTo(aString, mozilla::fallible)) {
+      aString.AllocFailed(aString.Length() + GetLength());
+    }
+  }
+
+  /**
+   * Append the contents of this string fragment to aString
+   * @return false if an out of memory condition is detected, true otherwise
+   */
+  MOZ_MUST_USE
+  bool AppendTo(nsAString& aString,
+                const mozilla::fallible_t& aFallible) const {
+    if (mState.mIs2b) {
+      if (aString.IsEmpty()) {
+        m2b->ToString(mState.mLength, aString);
+        return true;
+      }
+      bool ok = aString.Append(Get2b(), mState.mLength, aFallible);
+      if (!ok) {
+        return false;
+      }
+
+      return true;
+    } else {
+      return AppendASCIItoUTF16(Substring(m1b, mState.mLength), aString,
+                                aFallible);
+    }
+  }
+
+  /**
+   * Append a substring of the contents of this string fragment to aString.
+   * @param aOffset where to start the substring in this text fragment
+   * @param aLength the length of the substring
+   */
+  void AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength) const {
+    if (!AppendTo(aString, aOffset, aLength, mozilla::fallible)) {
+      aString.AllocFailed(aString.Length() + aLength);
+    }
+  }
+
+  /**
+   * Append a substring of the contents of this string fragment to aString.
+   * @param aString the string in which to append
+   * @param aOffset where to start the substring in this text fragment
+   * @param aLength the length of the substring
+   * @return false if an out of memory condition is detected, true otherwise
+   */
+  MOZ_MUST_USE
+  bool AppendTo(nsAString& aString, int32_t aOffset, int32_t aLength,
+                const mozilla::fallible_t& aFallible) const {
+    if (mState.mIs2b) {
+      bool ok = aString.Append(Get2b() + aOffset, aLength, aFallible);
+      if (!ok) {
+        return false;
+      }
+
+      return true;
+    } else {
+      return AppendASCIItoUTF16(Substring(m1b + aOffset, aLength), aString,
+                                aFallible);
+    }
+  }
+
+  /**
+   * Make a copy of the fragments contents starting at offset for
+   * count characters. The offset and count will be adjusted to
+   * lie within the fragments data. The fragments data is converted if
+   * necessary.
+   */
+  void CopyTo(char16_t* aDest, int32_t aOffset, int32_t aCount);
+
+  /**
+   * Return the character in the text-fragment at the given
+   * index. This always returns a char16_t.
+   */
+  char16_t CharAt(int32_t aIndex) const {
+    MOZ_ASSERT(uint32_t(aIndex) < mState.mLength, "bad index");
+    return mState.mIs2b ? Get2b()[aIndex]
+                        : static_cast<unsigned char>(m1b[aIndex]);
+  }
+
+  /**
+   * IsHighSurrogateFollowedByLowSurrogateAt() returns true if character at
+   * aIndex is high surrogate and it's followed by low surrogate.
+   */
+  inline bool IsHighSurrogateFollowedByLowSurrogateAt(int32_t aIndex) const {
+    MOZ_ASSERT(aIndex >= 0);
+    MOZ_ASSERT(aIndex < mState.mLength);
+    if (!mState.mIs2b || aIndex + 1 >= mState.mLength) {
+      return false;
+    }
+    return NS_IS_SURROGATE_PAIR(Get2b()[aIndex], Get2b()[aIndex + 1]);
+  }
+
+  /**
+   * IsLowSurrogateFollowingHighSurrogateAt() returns true if character at
+   * aIndex is low surrogate and it follows high surrogate.
+   */
+  inline bool IsLowSurrogateFollowingHighSurrogateAt(int32_t aIndex) const {
+    MOZ_ASSERT(aIndex >= 0);
+    MOZ_ASSERT(aIndex < mState.mLength);
+    if (!mState.mIs2b || aIndex <= 0) {
+      return false;
+    }
+    return NS_IS_SURROGATE_PAIR(Get2b()[aIndex - 1], Get2b()[aIndex]);
+  }
+
+  /**
+   * ScalarValueAt() returns a Unicode scalar value at aIndex.  If the character
+   * at aIndex is a high surrogate followed by low surrogate, returns character
+   * code for the pair.  If the index is low surrogate, or a high surrogate but
+   * not in a pair, returns 0.
+   */
+  inline char32_t ScalarValueAt(int32_t aIndex) const {
+    MOZ_ASSERT(aIndex >= 0);
+    MOZ_ASSERT(aIndex < mState.mLength);
+    if (!mState.mIs2b) {
+      return static_cast<unsigned char>(m1b[aIndex]);
+    }
+    char16_t ch = Get2b()[aIndex];
+    if (!IS_SURROGATE(ch)) {
+      return ch;
+    }
+    if (aIndex + 1 < mState.mLength && NS_IS_HIGH_SURROGATE(ch)) {
+      char16_t nextCh = Get2b()[aIndex + 1];
+      if (NS_IS_LOW_SURROGATE(nextCh)) {
+        return SURROGATE_TO_UCS4(ch, nextCh);
+      }
+    }
+    return 0;
+  }
+
+  void SetBidi(bool aBidi) { mState.mIsBidi = aBidi; }
+
+  struct FragmentBits {
+    // uint32_t to ensure that the values are unsigned, because we
+    // want 0/1, not 0/-1!
+    // Making these bool causes Windows to not actually pack them,
+    // which causes crashes because we assume this structure is no more than
+    // 32 bits!
+    uint32_t mInHeap : 1;
+    uint32_t mIs2b : 1;
+    uint32_t mIsBidi : 1;
+    // Note that when you change the bits of mLength, you also need to change
+    // NS_MAX_TEXT_FRAGMENT_LENGTH.
+    uint32_t mLength : 29;
+  };
+
+#define NS_MAX_TEXT_FRAGMENT_LENGTH (static_cast<uint32_t>(0x1FFFFFFF))
+
+  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+  /**
+   * Check whether the text in this fragment is the same as the text in the
+   * other fragment.
+   */
+  MOZ_MUST_USE bool TextEquals(const nsTextFragment& aOther) const;
+
+ private:
+  void ReleaseText();
+
+  /**
+   * Scan the contents of the fragment and turn on mState.mIsBidi if it
+   * includes any Bidi characters.
+   */
+  void UpdateBidiFlag(const char16_t* aBuffer, uint32_t aLength);
+
+  union {
+    nsStringBuffer* m2b;
+    const char* m1b;  // This is const since it can point to shared data
+  };
+
+  union {
+    uint32_t mAllBits;
+    FragmentBits mState;
+  };
+};
+
+#endif /* nsTextFragment_h___ */