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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
commit | 26a029d407be480d791972afb5975cf62c9360a6 (patch) | |
tree | f435a8308119effd964b339f76abb83a57c29483 /third_party/libwebrtc/rtc_base/bitstream_reader.cc | |
parent | Initial commit. (diff) | |
download | firefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz firefox-26a029d407be480d791972afb5975cf62c9360a6.zip |
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/libwebrtc/rtc_base/bitstream_reader.cc')
-rw-r--r-- | third_party/libwebrtc/rtc_base/bitstream_reader.cc | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/bitstream_reader.cc b/third_party/libwebrtc/rtc_base/bitstream_reader.cc new file mode 100644 index 0000000000..3e1b94d8d4 --- /dev/null +++ b/third_party/libwebrtc/rtc_base/bitstream_reader.cc @@ -0,0 +1,167 @@ +/* + * Copyright 2021 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 "rtc_base/bitstream_reader.h" + +#include <stdint.h> + +#include <limits> + +#include "absl/numeric/bits.h" +#include "rtc_base/checks.h" +#include "rtc_base/numerics/safe_conversions.h" + +namespace webrtc { + +uint64_t BitstreamReader::ReadBits(int bits) { + RTC_DCHECK_GE(bits, 0); + RTC_DCHECK_LE(bits, 64); + set_last_read_is_verified(false); + + if (remaining_bits_ < bits) { + remaining_bits_ -= bits; + return 0; + } + + int remaining_bits_in_first_byte = remaining_bits_ % 8; + remaining_bits_ -= bits; + if (bits < remaining_bits_in_first_byte) { + // Reading fewer bits than what's left in the current byte, just + // return the portion of this byte that is needed. + int offset = (remaining_bits_in_first_byte - bits); + return ((*bytes_) >> offset) & ((1 << bits) - 1); + } + + uint64_t result = 0; + if (remaining_bits_in_first_byte > 0) { + // Read all bits that were left in the current byte and consume that byte. + bits -= remaining_bits_in_first_byte; + uint8_t mask = (1 << remaining_bits_in_first_byte) - 1; + result = static_cast<uint64_t>(*bytes_ & mask) << bits; + ++bytes_; + } + + // Read as many full bytes as we can. + while (bits >= 8) { + bits -= 8; + result |= uint64_t{*bytes_} << bits; + ++bytes_; + } + // Whatever is left to read is smaller than a byte, so grab just the needed + // bits and shift them into the lowest bits. + if (bits > 0) { + result |= (*bytes_ >> (8 - bits)); + } + return result; +} + +int BitstreamReader::ReadBit() { + set_last_read_is_verified(false); + --remaining_bits_; + if (remaining_bits_ < 0) { + return 0; + } + + int bit_position = remaining_bits_ % 8; + if (bit_position == 0) { + // Read the last bit from current byte and move to the next byte. + return (*bytes_++) & 0x01; + } + + return (*bytes_ >> bit_position) & 0x01; +} + +void BitstreamReader::ConsumeBits(int bits) { + RTC_DCHECK_GE(bits, 0); + set_last_read_is_verified(false); + if (remaining_bits_ < bits) { + Invalidate(); + return; + } + + int remaining_bytes = (remaining_bits_ + 7) / 8; + remaining_bits_ -= bits; + int new_remaining_bytes = (remaining_bits_ + 7) / 8; + bytes_ += (remaining_bytes - new_remaining_bytes); +} + +uint32_t BitstreamReader::ReadNonSymmetric(uint32_t num_values) { + RTC_DCHECK_GT(num_values, 0); + RTC_DCHECK_LE(num_values, uint32_t{1} << 31); + + int width = absl::bit_width(num_values); + uint32_t num_min_bits_values = (uint32_t{1} << width) - num_values; + + uint64_t val = ReadBits(width - 1); + if (val < num_min_bits_values) { + return val; + } + return (val << 1) + ReadBit() - num_min_bits_values; +} + +uint32_t BitstreamReader::ReadExponentialGolomb() { + // Count the number of leading 0. + int zero_bit_count = 0; + while (ReadBit() == 0) { + if (++zero_bit_count >= 32) { + // Golob value won't fit into 32 bits of the return value. Fail the parse. + Invalidate(); + return 0; + } + } + + // The bit count of the value is the number of zeros + 1. + // However the first '1' was already read above. + return (uint32_t{1} << zero_bit_count) + + rtc::dchecked_cast<uint32_t>(ReadBits(zero_bit_count)) - 1; +} + +int BitstreamReader::ReadSignedExponentialGolomb() { + uint32_t unsigned_val = ReadExponentialGolomb(); + if ((unsigned_val & 1) == 0) { + return -static_cast<int>(unsigned_val / 2); + } else { + return (unsigned_val + 1) / 2; + } +} + +uint64_t BitstreamReader::ReadLeb128() { + uint64_t decoded = 0; + size_t i = 0; + uint8_t byte; + // A LEB128 value can in theory be arbitrarily large, but for convenience sake + // consider it invalid if it can't fit in an uint64_t. + do { + byte = Read<uint8_t>(); + decoded += + (static_cast<uint64_t>(byte & 0x7f) << static_cast<uint64_t>(7 * i)); + ++i; + } while (i < 10 && (byte & 0x80)); + + // The first 9 bytes represent the first 63 bits. The tenth byte can therefore + // not be larger than 1 as it would overflow an uint64_t. + if (i == 10 && byte > 1) { + Invalidate(); + } + + return Ok() ? decoded : 0; +} + +std::string BitstreamReader::ReadString(int num_bytes) { + std::string res; + res.reserve(num_bytes); + for (int i = 0; i < num_bytes; ++i) { + res += Read<uint8_t>(); + } + + return Ok() ? res : std::string(); +} + +} // namespace webrtc |