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 #include "ui/gfx/utf16_indexing.h" 6 7 #include "base/logging.h" 8 #include "base/third_party/icu/icu_utf.h" 9 10 namespace gfx { 11 12 bool IsValidCodePointIndex(const base::string16& s, size_t index) { 13 return index == 0 || index == s.length() || 14 !(CBU16_IS_TRAIL(s[index]) && CBU16_IS_LEAD(s[index - 1])); 15 } 16 17 ptrdiff_t UTF16IndexToOffset(const base::string16& s, size_t base, size_t pos) { 18 // The indices point between UTF-16 words (range 0 to s.length() inclusive). 19 // In order to consistently handle indices that point to the middle of a 20 // surrogate pair, we count the first word in that surrogate pair and not 21 // the second. The test "s[i] is not the second half of a surrogate pair" is 22 // "IsValidCodePointIndex(s, i)". 23 DCHECK_LE(base, s.length()); 24 DCHECK_LE(pos, s.length()); 25 ptrdiff_t delta = 0; 26 while (base < pos) 27 delta += IsValidCodePointIndex(s, base++) ? 1 : 0; 28 while (pos < base) 29 delta -= IsValidCodePointIndex(s, pos++) ? 1 : 0; 30 return delta; 31 } 32 33 size_t UTF16OffsetToIndex(const base::string16& s, 34 size_t base, 35 ptrdiff_t offset) { 36 DCHECK_LE(base, s.length()); 37 // As in UTF16IndexToOffset, we count the first half of a surrogate pair, not 38 // the second. When stepping from pos to pos+1 we check s[pos:pos+1] == s[pos] 39 // (Python syntax), hence pos++. When stepping from pos to pos-1 we check 40 // s[pos-1], hence --pos. 41 size_t pos = base; 42 while (offset > 0 && pos < s.length()) 43 offset -= IsValidCodePointIndex(s, pos++) ? 1 : 0; 44 while (offset < 0 && pos > 0) 45 offset += IsValidCodePointIndex(s, --pos) ? 1 : 0; 46 // If offset != 0 then we ran off the edge of the string, which is a contract 47 // violation but is handled anyway (by clamping) in release for safety. 48 DCHECK_EQ(offset, 0); 49 // Since the second half of a surrogate pair has "length" zero, there is an 50 // ambiguity in the returned position. Resolve it by always returning a valid 51 // index. 52 if (!IsValidCodePointIndex(s, pos)) 53 ++pos; 54 return pos; 55 } 56 57 } // namespace gfx 58
