String TextCodecUTF8::Decode(const char* bytes,
                             wtf_size_t length,
                             FlushBehavior flush,
                             bool stop_on_error,
                             bool& saw_error) {
  const bool do_flush = flush != FlushBehavior::kDoNotFlush;
  StringBuffer<LChar> buffer(partial_sequence_size_ + length);
 
   const uint8_t* source = reinterpret_cast<const uint8_t*>(bytes);
   const uint8_t* end = source + length;
  const uint8_t* aligned_end = AlignToMachineWord(end);
  LChar* destination = buffer.Characters();

  do {
    if (partial_sequence_size_) {
      LChar* destination_for_handle_partial_sequence = destination;
      const uint8_t* source_for_handle_partial_sequence = source;
      if (HandlePartialSequence(destination_for_handle_partial_sequence,
                                source_for_handle_partial_sequence, end,
                                do_flush, stop_on_error, saw_error)) {
        source = source_for_handle_partial_sequence;
        goto upConvertTo16Bit;
      }
      destination = destination_for_handle_partial_sequence;
      source = source_for_handle_partial_sequence;
      if (partial_sequence_size_)
        break;
    }

    while (source < end) {
      if (IsASCII(*source)) {
        if (IsAlignedToMachineWord(source)) {
          while (source < aligned_end) {
            MachineWord chunk =
                *reinterpret_cast_ptr<const MachineWord*>(source);
            if (!IsAllASCII<LChar>(chunk))
              break;
            CopyASCIIMachineWord(destination, source);
            source += sizeof(MachineWord);
            destination += sizeof(MachineWord);
          }
          if (source == end)
            break;
          if (!IsASCII(*source))
            continue;
        }
        *destination++ = *source++;
        continue;
      }
      int count = NonASCIISequenceLength(*source);
      int character;
      if (count == 0) {
        character = kNonCharacter1;
      } else {
        if (count > end - source) {
          SECURITY_DCHECK(end - source <
                          static_cast<ptrdiff_t>(sizeof(partial_sequence_)));
          DCHECK(!partial_sequence_size_);
          partial_sequence_size_ = static_cast<wtf_size_t>(end - source);
          memcpy(partial_sequence_, source, partial_sequence_size_);
          source = end;
          break;
        }
        character = DecodeNonASCIISequence(source, count);
      }
      if (IsNonCharacter(character)) {
        saw_error = true;
        if (stop_on_error)
          break;

        goto upConvertTo16Bit;
      }
      if (character > 0xff)
        goto upConvertTo16Bit;

      source += count;
      *destination++ = static_cast<LChar>(character);
    }
  } while (do_flush && partial_sequence_size_);

  buffer.Shrink(static_cast<wtf_size_t>(destination - buffer.Characters()));

   return String::Adopt(buffer);
 
 upConvertTo16Bit:
  StringBuffer<UChar> buffer16(partial_sequence_size_ + length);
 
   UChar* destination16 = buffer16.Characters();
 
  for (LChar* converted8 = buffer.Characters(); converted8 < destination;)
    *destination16++ = *converted8++;

  do {
    if (partial_sequence_size_) {
      UChar* destination_for_handle_partial_sequence = destination16;
      const uint8_t* source_for_handle_partial_sequence = source;
      HandlePartialSequence(destination_for_handle_partial_sequence,
                            source_for_handle_partial_sequence, end, do_flush,
                            stop_on_error, saw_error);
      destination16 = destination_for_handle_partial_sequence;
      source = source_for_handle_partial_sequence;
      if (partial_sequence_size_)
        break;
    }

    while (source < end) {
      if (IsASCII(*source)) {
        if (IsAlignedToMachineWord(source)) {
          while (source < aligned_end) {
            MachineWord chunk =
                *reinterpret_cast_ptr<const MachineWord*>(source);
            if (!IsAllASCII<LChar>(chunk))
              break;
            CopyASCIIMachineWord(destination16, source);
            source += sizeof(MachineWord);
            destination16 += sizeof(MachineWord);
          }
          if (source == end)
            break;
          if (!IsASCII(*source))
            continue;
        }
        *destination16++ = *source++;
        continue;
      }
      int count = NonASCIISequenceLength(*source);
      int character;
      if (count == 0) {
        character = kNonCharacter1;
      } else {
        if (count > end - source) {
          SECURITY_DCHECK(end - source <
                          static_cast<ptrdiff_t>(sizeof(partial_sequence_)));
          DCHECK(!partial_sequence_size_);
          partial_sequence_size_ = static_cast<wtf_size_t>(end - source);
          memcpy(partial_sequence_, source, partial_sequence_size_);
          source = end;
          break;
        }
        character = DecodeNonASCIISequence(source, count);
      }
      if (IsNonCharacter(character)) {
        saw_error = true;
        if (stop_on_error)
          break;
        *destination16++ = kReplacementCharacter;
        source -= character;
        continue;
      }
      source += count;
      destination16 = AppendCharacter(destination16, character);
    }
  } while (do_flush && partial_sequence_size_);

  buffer16.Shrink(
      static_cast<wtf_size_t>(destination16 - buffer16.Characters()));

  return String::Adopt(buffer16);
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.