12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152 |
- // Copyright (c) 2012 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #ifndef UI_GFX_UTF16_INDEXING_H_
- #define UI_GFX_UTF16_INDEXING_H_
- #include <stddef.h>
- #include <string>
- #include "ui/gfx/gfx_export.h"
- namespace gfx {
- // Returns false if s[index-1] is a high surrogate and s[index] is a low
- // surrogate, true otherwise.
- GFX_EXPORT bool IsValidCodePointIndex(const std::u16string& s, size_t index);
- // |UTF16IndexToOffset| returns the number of code points between |base| and
- // |pos| in the given string. |UTF16OffsetToIndex| returns the index that is
- // |offset| code points away from the given |base| index. These functions are
- // named after glib's |g_utf8_pointer_to_offset| and |g_utf8_offset_to_pointer|,
- // which perform the same function for UTF-8. As in glib, it is an error to
- // pass an |offset| that walks off the edge of the string.
- //
- // These functions attempt to deal with invalid use of UTF-16 surrogates in a
- // way that makes as much sense as possible: unpaired surrogates are treated as
- // single characters, and if an argument index points to the middle of a valid
- // surrogate pair, it is treated as though it pointed to the end of that pair.
- // The index returned by |UTF16OffsetToIndex| never points to the middle of a
- // surrogate pair.
- //
- // The following identities hold:
- // If |s| contains no surrogate pairs, then
- // UTF16IndexToOffset(s, base, pos) == pos - base
- // UTF16OffsetToIndex(s, base, offset) == base + offset
- // If |pos| does not point to the middle of a surrogate pair, then
- // UTF16OffsetToIndex(s, base, UTF16IndexToOffset(s, base, pos)) == pos
- // Always,
- // UTF16IndexToOffset(s, base, UTF16OffsetToIndex(s, base, ofs)) == ofs
- // UTF16IndexToOffset(s, i, j) == -UTF16IndexToOffset(s, j, i)
- GFX_EXPORT ptrdiff_t UTF16IndexToOffset(const std::u16string& s,
- size_t base,
- size_t pos);
- GFX_EXPORT size_t UTF16OffsetToIndex(const std::u16string& s,
- size_t base,
- ptrdiff_t offset);
- } // namespace gfx
- #endif // UI_GFX_UTF16_INDEXING_H_
|