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// 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 "base/strings/string16.h"
#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 base::string16& 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 base::string16& s,
size_t base,
size_t pos);
GFX_EXPORT size_t UTF16OffsetToIndex(const base::string16& s,
size_t base,
ptrdiff_t offset);
} // namespace gfx
#endif // UI_GFX_UTF16_INDEXING_H_
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