Move webrtc/{base => rtc_base}

webrtc/base/bitbuffer.cc

-/*
- *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include "webrtc/base/bitbuffer.h"
-
-#include <algorithm>
-#include <limits>
-
-#include "webrtc/base/checks.h"
-
-namespace {
-
-// Returns the lowest (right-most) |bit_count| bits in |byte|.
-uint8_t LowestBits(uint8_t byte, size_t bit_count) {
-  RTC_DCHECK_LE(bit_count, 8);
-  return byte & ((1 << bit_count) - 1);
-}
-
-// Returns the highest (left-most) |bit_count| bits in |byte|, shifted to the
-// lowest bits (to the right).
-uint8_t HighestBits(uint8_t byte, size_t bit_count) {
-  RTC_DCHECK_LE(bit_count, 8);
-  uint8_t shift = 8 - static_cast<uint8_t>(bit_count);
-  uint8_t mask = 0xFF << shift;
-  return (byte & mask) >> shift;
-}
-
-// Returns the highest byte of |val| in a uint8_t.
-uint8_t HighestByte(uint64_t val) {
-  return static_cast<uint8_t>(val >> 56);
-}
-
-// Returns the result of writing partial data from |source|, of
-// |source_bit_count| size in the highest bits, to |target| at
-// |target_bit_offset| from the highest bit.
-uint8_t WritePartialByte(uint8_t source,
-                         size_t source_bit_count,
-                         uint8_t target,
-                         size_t target_bit_offset) {
-  RTC_DCHECK(target_bit_offset < 8);
-  RTC_DCHECK(source_bit_count < 9);
-  RTC_DCHECK(source_bit_count <= (8 - target_bit_offset));
-  // Generate a mask for just the bits we're going to overwrite, so:
-  uint8_t mask =
-      // The number of bits we want, in the most significant bits...
-      static_cast<uint8_t>(0xFF << (8 - source_bit_count))
-      // ...shifted over to the target offset from the most signficant bit.
-      >> target_bit_offset;
-
-  // We want the target, with the bits we'll overwrite masked off, or'ed with
-  // the bits from the source we want.
-  return (target & ~mask) | (source >> target_bit_offset);
-}
-
-// Counts the number of bits used in the binary representation of val.
-size_t CountBits(uint64_t val) {
-  size_t bit_count = 0;
-  while (val != 0) {
-    bit_count++;
-    val >>= 1;
-  }
-  return bit_count;
-}
-
-}  // namespace
-
-namespace rtc {
-
-BitBuffer::BitBuffer(const uint8_t* bytes, size_t byte_count)
-    : bytes_(bytes), byte_count_(byte_count), byte_offset_(), bit_offset_() {
-  RTC_DCHECK(static_cast<uint64_t>(byte_count_) <=
-             std::numeric_limits<uint32_t>::max());
-}
-
-uint64_t BitBuffer::RemainingBitCount() const {
-  return (static_cast<uint64_t>(byte_count_) - byte_offset_) * 8 - bit_offset_;
-}
-
-bool BitBuffer::ReadUInt8(uint8_t* val) {
-  uint32_t bit_val;
-  if (!ReadBits(&bit_val, sizeof(uint8_t) * 8)) {
-    return false;
-  }
-  RTC_DCHECK(bit_val <= std::numeric_limits<uint8_t>::max());
-  *val = static_cast<uint8_t>(bit_val);
-  return true;
-}
-
-bool BitBuffer::ReadUInt16(uint16_t* val) {
-  uint32_t bit_val;
-  if (!ReadBits(&bit_val, sizeof(uint16_t) * 8)) {
-    return false;
-  }
-  RTC_DCHECK(bit_val <= std::numeric_limits<uint16_t>::max());
-  *val = static_cast<uint16_t>(bit_val);
-  return true;
-}
-
-bool BitBuffer::ReadUInt32(uint32_t* val) {
-  return ReadBits(val, sizeof(uint32_t) * 8);
-}
-
-bool BitBuffer::PeekBits(uint32_t* val, size_t bit_count) {
-  if (!val || bit_count > RemainingBitCount() || bit_count > 32) {
-    return false;
-  }
-  const uint8_t* bytes = bytes_ + byte_offset_;
-  size_t remaining_bits_in_current_byte = 8 - bit_offset_;
-  uint32_t bits = LowestBits(*bytes++, remaining_bits_in_current_byte);
-  // If we're reading fewer bits than what's left in the current byte, just
-  // return the portion of this byte that we need.
-  if (bit_count < remaining_bits_in_current_byte) {
-    *val = HighestBits(bits, bit_offset_ + bit_count);
-    return true;
-  }
-  // Otherwise, subtract what we've read from the bit count and read as many
-  // full bytes as we can into bits.
-  bit_count -= remaining_bits_in_current_byte;
-  while (bit_count >= 8) {
-    bits = (bits << 8) | *bytes++;
-    bit_count -= 8;
-  }
-  // Whatever we have left is smaller than a byte, so grab just the bits we need
-  // and shift them into the lowest bits.
-  if (bit_count > 0) {
-    bits <<= bit_count;
-    bits |= HighestBits(*bytes, bit_count);
-  }
-  *val = bits;
-  return true;
-}
-
-bool BitBuffer::ReadBits(uint32_t* val, size_t bit_count) {
-  return PeekBits(val, bit_count) && ConsumeBits(bit_count);
-}
-
-bool BitBuffer::ConsumeBytes(size_t byte_count) {
-  return ConsumeBits(byte_count * 8);
-}
-
-bool BitBuffer::ConsumeBits(size_t bit_count) {
-  if (bit_count > RemainingBitCount()) {
-    return false;
-  }
-
-  byte_offset_ += (bit_offset_ + bit_count) / 8;
-  bit_offset_ = (bit_offset_ + bit_count) % 8;
-  return true;
-}
-
-bool BitBuffer::ReadExponentialGolomb(uint32_t* val) {
-  if (!val) {
-    return false;
-  }
-  // Store off the current byte/bit offset, in case we want to restore them due
-  // to a failed parse.
-  size_t original_byte_offset = byte_offset_;
-  size_t original_bit_offset = bit_offset_;
-
-  // Count the number of leading 0 bits by peeking/consuming them one at a time.
-  size_t zero_bit_count = 0;
-  uint32_t peeked_bit;
-  while (PeekBits(&peeked_bit, 1) && peeked_bit == 0) {
-    zero_bit_count++;
-    ConsumeBits(1);
-  }
-
-  // We should either be at the end of the stream, or the next bit should be 1.
-  RTC_DCHECK(!PeekBits(&peeked_bit, 1) || peeked_bit == 1);
-
-  // The bit count of the value is the number of zeros + 1. Make sure that many
-  // bits fits in a uint32_t and that we have enough bits left for it, and then
-  // read the value.
-  size_t value_bit_count = zero_bit_count + 1;
-  if (value_bit_count > 32 || !ReadBits(val, value_bit_count)) {
-    RTC_CHECK(Seek(original_byte_offset, original_bit_offset));
-    return false;
-  }
-  *val -= 1;
-  return true;
-}
-
-bool BitBuffer::ReadSignedExponentialGolomb(int32_t* val) {
-  uint32_t unsigned_val;
-  if (!ReadExponentialGolomb(&unsigned_val)) {
-    return false;
-  }
-  if ((unsigned_val & 1) == 0) {
-    *val = -static_cast<int32_t>(unsigned_val / 2);
-  } else {
-    *val = (unsigned_val + 1) / 2;
-  }
-  return true;
-}
-
-void BitBuffer::GetCurrentOffset(
-    size_t* out_byte_offset, size_t* out_bit_offset) {
-  RTC_CHECK(out_byte_offset != nullptr);
-  RTC_CHECK(out_bit_offset != nullptr);
-  *out_byte_offset = byte_offset_;
-  *out_bit_offset = bit_offset_;
-}
-
-bool BitBuffer::Seek(size_t byte_offset, size_t bit_offset) {
-  if (byte_offset > byte_count_ || bit_offset > 7 ||
-      (byte_offset == byte_count_ && bit_offset > 0)) {
-    return false;
-  }
-  byte_offset_ = byte_offset;
-  bit_offset_ = bit_offset;
-  return true;
-}
-
-BitBufferWriter::BitBufferWriter(uint8_t* bytes, size_t byte_count)
-    : BitBuffer(bytes, byte_count), writable_bytes_(bytes) {
-}
-
-bool BitBufferWriter::WriteUInt8(uint8_t val) {
-  return WriteBits(val, sizeof(uint8_t) * 8);
-}
-
-bool BitBufferWriter::WriteUInt16(uint16_t val) {
-  return WriteBits(val, sizeof(uint16_t) * 8);
-}
-
-bool BitBufferWriter::WriteUInt32(uint32_t val) {
-  return WriteBits(val, sizeof(uint32_t) * 8);
-}
-
-bool BitBufferWriter::WriteBits(uint64_t val, size_t bit_count) {
-  if (bit_count > RemainingBitCount()) {
-    return false;
-  }
-  size_t total_bits = bit_count;
-
-  // For simplicity, push the bits we want to read from val to the highest bits.
-  val <<= (sizeof(uint64_t) * 8 - bit_count);
-
-  uint8_t* bytes = writable_bytes_ + byte_offset_;
-
-  // The first byte is relatively special; the bit offset to write to may put us
-  // in the middle of the byte, and the total bit count to write may require we
-  // save the bits at the end of the byte.
-  size_t remaining_bits_in_current_byte = 8 - bit_offset_;
-  size_t bits_in_first_byte =
-      std::min(bit_count, remaining_bits_in_current_byte);
-  *bytes = WritePartialByte(
-      HighestByte(val), bits_in_first_byte, *bytes, bit_offset_);
-  if (bit_count <= remaining_bits_in_current_byte) {
-    // Nothing left to write, so quit early.
-    return ConsumeBits(total_bits);
-  }
-
-  // Subtract what we've written from the bit count, shift it off the value, and
-  // write the remaining full bytes.
-  val <<= bits_in_first_byte;
-  bytes++;
-  bit_count -= bits_in_first_byte;
-  while (bit_count >= 8) {
-    *bytes++ = HighestByte(val);
-    val <<= 8;
-    bit_count -= 8;
-  }
-
-  // Last byte may also be partial, so write the remaining bits from the top of
-  // val.
-  if (bit_count > 0) {
-    *bytes = WritePartialByte(HighestByte(val), bit_count, *bytes, 0);
-  }
-
-  // All done! Consume the bits we've written.
-  return ConsumeBits(total_bits);
-}
-
-bool BitBufferWriter::WriteExponentialGolomb(uint32_t val) {
-  // We don't support reading UINT32_MAX, because it doesn't fit in a uint32_t
-  // when encoded, so don't support writing it either.
-  if (val == std::numeric_limits<uint32_t>::max()) {
-    return false;
-  }
-  uint64_t val_to_encode = static_cast<uint64_t>(val) + 1;
-
-  // We need to write CountBits(val+1) 0s and then val+1. Since val (as a
-  // uint64_t) has leading zeros, we can just write the total golomb encoded
-  // size worth of bits, knowing the value will appear last.
-  return WriteBits(val_to_encode, CountBits(val_to_encode) * 2 - 1);
-}
-
-bool BitBufferWriter::WriteSignedExponentialGolomb(int32_t val) {
-  if (val == 0) {
-    return WriteExponentialGolomb(0);
-  } else if (val > 0) {
-    uint32_t signed_val = val;
-    return WriteExponentialGolomb((signed_val * 2) - 1);
-  } else {
-    if (val == std::numeric_limits<int32_t>::min())
-      return false;  // Not supported, would cause overflow.
-    uint32_t signed_val = -val;
-    return WriteExponentialGolomb(signed_val * 2);
-  }
-}
-
-}  // namespace rtc