third_party/chromium/base/strings/utf_string_conversion_utils.cc

// Copyright (c) 2009 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.

#include "base/strings/utf_string_conversion_utils.h"

#include "base/third_party/icu/icu_utf.h"

namespace base {

// ReadUnicodeCharacter --------------------------------------------------------

bool ReadUnicodeCharacter(const char* src,
                          int32_t src_len,
                          int32_t* char_index,
                          uint32_t* code_point_out) {
  // U8_NEXT expects to be able to use -1 to signal an error, so we must
  // use a signed type for code_point.  But this function returns false
  // on error anyway, so code_point_out is unsigned.
  int32_t code_point;
  CBU8_NEXT(src, *char_index, src_len, code_point);
  *code_point_out = static_cast<uint32_t>(code_point);

  // The ICU macro above moves to the next char, we want to point to the last
  // char consumed.
  (*char_index)--;

  // Validate the decoded value.
  return IsValidCodepoint(code_point);
}

// WriteUnicodeCharacter -------------------------------------------------------

size_t WriteUnicodeCharacter(uint32_t code_point, std::string* output) {
  if (code_point <= 0x7f) {
    // Fast path the common case of one byte.
    output->push_back(static_cast<char>(code_point));
    return 1;
  }


  // CBU8_APPEND_UNSAFE can append up to 4 bytes.
  size_t char_offset = output->length();
  size_t original_char_offset = char_offset;
  output->resize(char_offset + CBU8_MAX_LENGTH);

  CBU8_APPEND_UNSAFE(&(*output)[0], char_offset, code_point);

  // CBU8_APPEND_UNSAFE will advance our pointer past the inserted character, so
  // it will represent the new length of the string.
  output->resize(char_offset);
  return char_offset - original_char_offset;
}

// Generalized Unicode converter -----------------------------------------------

template<typename CHAR>
void PrepareForUTF8Output(const CHAR* src,
                          size_t src_len,
                          std::string* output) {
  output->clear();
  if (src_len == 0)
    return;
  if (src[0] < 0x80) {
    // Assume that the entire input will be ASCII.
    output->reserve(src_len);
  } else {
    // Assume that the entire input is non-ASCII and will have 3 bytes per char.
    output->reserve(src_len * 3);
  }
}

template<typename STRING>
void PrepareForUTF16Or32Output(const char* src,
                               size_t src_len,
                               STRING* output) {
  output->clear();
  if (src_len == 0)
    return;
  if (static_cast<unsigned char>(src[0]) < 0x80) {
    // Assume the input is all ASCII, which means 1:1 correspondence.
    output->reserve(src_len);
  } else {
    // Otherwise assume that the UTF-8 sequences will have 2 bytes for each
    // character.
    output->reserve(src_len / 2);
  }
}

}  // namespace base