base/i18n/streaming_utf8_validator.cc

   1 // Copyright 2014 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 // This implementation doesn't use ICU. The ICU macros are oriented towards
   6 // character-at-a-time processing, whereas byte-at-a-time processing is easier
   7 // with streaming input.
   8
   9 #include "base/i18n/streaming_utf8_validator.h"
  10
  11 #include "base/i18n/utf8_validator_tables.h"
  12 #include "base/logging.h"
  13
  14 namespace base {
  15 namespace {
  16
  17 uint8 StateTableLookup(uint8 offset) {
  18   DCHECK_LT(offset, internal::kUtf8ValidatorTablesSize);
  19   return internal::kUtf8ValidatorTables[offset];
  20 }
  21
  22 }  // namespace
  23
  24 StreamingUtf8Validator::State StreamingUtf8Validator::AddBytes(const char* data,
  25                                                                size_t size) {
  26   // Copy |state_| into a local variable so that the compiler doesn't have to be
  27   // careful of aliasing.
  28   uint8 state = state_;
  29   for (const char* p = data; p != data + size; ++p) {
  30     if ((*p & 0x80) == 0) {
  31       if (state == 0)
  32         continue;
  33       state = internal::I18N_UTF8_VALIDATOR_INVALID_INDEX;
  34       break;
  35     }
  36     const uint8 shift_amount = StateTableLookup(state);
  37     const uint8 shifted_char = (*p & 0x7F) >> shift_amount;
  38     state = StateTableLookup(state + shifted_char + 1);
  39     // State may be INVALID here, but this code is optimised for the case of
  40     // valid UTF-8 and it is more efficient (by about 2%) to not attempt an
  41     // early loop exit unless we hit an ASCII character.
  42   }
  43   state_ = state;
  44   return state == 0 ? VALID_ENDPOINT
  45       : state == internal::I18N_UTF8_VALIDATOR_INVALID_INDEX
  46       ? INVALID
  47       : VALID_MIDPOINT;
  48 }
  49
  50 void StreamingUtf8Validator::Reset() {
  51   state_ = 0u;
  52 }
  53
  54 bool StreamingUtf8Validator::Validate(const std::string& string) {
  55   return StreamingUtf8Validator().AddBytes(string.data(), string.size()) ==
  56          VALID_ENDPOINT;
  57 }
  58
  59 }  // namespace base