1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef UI_GFX_UTF16_INDEXING_H_ 6 #define UI_GFX_UTF16_INDEXING_H_ 7 8 #include "base/strings/string16.h" 9 #include "ui/gfx/gfx_export.h" 10 11 namespace gfx { 12 13 // Returns false if s[index-1] is a high surrogate and s[index] is a low 14 // surrogate, true otherwise. 15 GFX_EXPORT bool IsValidCodePointIndex(const base::string16& s, size_t index); 16 17 // |UTF16IndexToOffset| returns the number of code points between |base| and 18 // |pos| in the given string. |UTF16OffsetToIndex| returns the index that is 19 // |offset| code points away from the given |base| index. These functions are 20 // named after glib's |g_utf8_pointer_to_offset| and |g_utf8_offset_to_pointer|, 21 // which perform the same function for UTF-8. As in glib, it is an error to 22 // pass an |offset| that walks off the edge of the string. 23 // 24 // These functions attempt to deal with invalid use of UTF-16 surrogates in a 25 // way that makes as much sense as possible: unpaired surrogates are treated as 26 // single characters, and if an argument index points to the middle of a valid 27 // surrogate pair, it is treated as though it pointed to the end of that pair. 28 // The index returned by |UTF16OffsetToIndex| never points to the middle of a 29 // surrogate pair. 30 // 31 // The following identities hold: 32 // If |s| contains no surrogate pairs, then 33 // UTF16IndexToOffset(s, base, pos) == pos - base 34 // UTF16OffsetToIndex(s, base, offset) == base + offset 35 // If |pos| does not point to the middle of a surrogate pair, then 36 // UTF16OffsetToIndex(s, base, UTF16IndexToOffset(s, base, pos)) == pos 37 // Always, 38 // UTF16IndexToOffset(s, base, UTF16OffsetToIndex(s, base, ofs)) == ofs 39 // UTF16IndexToOffset(s, i, j) == -UTF16IndexToOffset(s, j, i) 40 GFX_EXPORT ptrdiff_t UTF16IndexToOffset(const base::string16& s, 41 size_t base, 42 size_t pos); 43 GFX_EXPORT size_t UTF16OffsetToIndex(const base::string16& s, 44 size_t base, 45 ptrdiff_t offset); 46 47 } // namespace gfx 48 49 #endif // UI_GFX_UTF16_INDEXING_H_ 50
