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// Copyright 2019 The libgav1 Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/utils/raw_bit_reader.h"
#include <cassert>
#include <limits>
#include "src/utils/common.h"
#include "src/utils/logging.h"
// Note <cinttypes> is only needed when logging is enabled (for the PRI*
// macros). It depends on the definition of LIBGAV1_ENABLE_LOGGING from
// logging.h, thus the non-standard header ordering.
#if LIBGAV1_ENABLE_LOGGING
#include <cinttypes>
#endif
namespace libgav1 {
namespace {
constexpr int kMaximumLeb128Size = 8;
constexpr uint8_t kLeb128ValueByteMask = 0x7f;
constexpr uint8_t kLeb128TerminationByteMask = 0x80;
uint8_t Mod8(size_t n) {
// Last 3 bits are the value of mod 8.
return n & 0x07;
}
size_t DivideBy8(size_t n, bool ceil) { return (n + (ceil ? 7 : 0)) >> 3; }
} // namespace
RawBitReader::RawBitReader(const uint8_t* data, size_t size)
: data_(data), bit_offset_(0), size_(size) {
assert(data_ != nullptr || size_ == 0);
}
int RawBitReader::ReadBitImpl() {
const size_t byte_offset = DivideBy8(bit_offset_, false);
const uint8_t byte = data_[byte_offset];
const uint8_t shift = 7 - Mod8(bit_offset_);
++bit_offset_;
return static_cast<int>((byte >> shift) & 0x01);
}
int RawBitReader::ReadBit() {
if (Finished()) return -1;
return ReadBitImpl();
}
int64_t RawBitReader::ReadLiteral(int num_bits) {
assert(num_bits <= 32);
if (!CanReadLiteral(num_bits)) return -1;
assert(num_bits > 0);
uint32_t literal = 0;
int bit = num_bits - 1;
do {
// ARM can combine a shift operation with a constant number of bits with
// some other operations, such as the OR operation.
// Here is an ARM disassembly example:
// orr w1, w0, w1, lsl #1
// which left shifts register w1 by 1 bit and OR the shift result with
// register w0.
// The next 2 lines are equivalent to:
// literal |= static_cast<uint32_t>(ReadBitImpl()) << bit;
literal <<= 1;
literal |= static_cast<uint32_t>(ReadBitImpl());
} while (--bit >= 0);
return literal;
}
bool RawBitReader::ReadInverseSignedLiteral(int num_bits, int* const value) {
assert(num_bits + 1 < 32);
*value = static_cast<int>(ReadLiteral(num_bits + 1));
if (*value == -1) return false;
const int sign_bit = 1 << num_bits;
if ((*value & sign_bit) != 0) {
*value -= 2 * sign_bit;
}
return true;
}
bool RawBitReader::ReadLittleEndian(int num_bytes, size_t* const value) {
// We must be at a byte boundary.
assert(Mod8(bit_offset_) == 0);
assert(num_bytes <= 4);
static_assert(sizeof(size_t) >= 4, "");
if (value == nullptr) return false;
size_t byte_offset = DivideBy8(bit_offset_, false);
if (Finished() || byte_offset + num_bytes > size_) {
LIBGAV1_DLOG(ERROR, "Not enough bits to read Little Endian value.");
return false;
}
*value = 0;
for (int i = 0; i < num_bytes; ++i) {
const size_t byte = data_[byte_offset];
*value |= (byte << (i * 8));
++byte_offset;
}
bit_offset_ = byte_offset * 8;
return true;
}
bool RawBitReader::ReadUnsignedLeb128(size_t* const value) {
// We must be at a byte boundary.
assert(Mod8(bit_offset_) == 0);
if (value == nullptr) return false;
uint64_t value64 = 0;
for (int i = 0; i < kMaximumLeb128Size; ++i) {
if (Finished()) {
LIBGAV1_DLOG(ERROR, "Not enough bits to read LEB128 value.");
return false;
}
const size_t byte_offset = DivideBy8(bit_offset_, false);
const uint8_t byte = data_[byte_offset];
bit_offset_ += 8;
value64 |= static_cast<uint64_t>(byte & kLeb128ValueByteMask) << (i * 7);
if ((byte & kLeb128TerminationByteMask) == 0) {
if (value64 != static_cast<size_t>(value64) ||
value64 > std::numeric_limits<uint32_t>::max()) {
LIBGAV1_DLOG(
ERROR, "LEB128 value (%" PRIu64 ") exceeded uint32_t maximum (%u).",
value64, std::numeric_limits<uint32_t>::max());
return false;
}
*value = static_cast<size_t>(value64);
return true;
}
}
LIBGAV1_DLOG(
ERROR,
"Exceeded kMaximumLeb128Size (%d) when trying to read LEB128 value",
kMaximumLeb128Size);
return false;
}
bool RawBitReader::ReadUvlc(uint32_t* const value) {
if (value == nullptr) return false;
int leading_zeros = 0;
while (true) {
const int bit = ReadBit();
if (bit == -1) {
LIBGAV1_DLOG(ERROR, "Not enough bits to read uvlc value.");
return false;
}
if (bit == 1) break;
++leading_zeros;
if (leading_zeros == 32) {
LIBGAV1_DLOG(ERROR,
"Exceeded maximum size (32) when trying to read uvlc value");
return false;
}
}
int literal;
if (leading_zeros != 0) {
literal = static_cast<int>(ReadLiteral(leading_zeros));
if (literal == -1) {
LIBGAV1_DLOG(ERROR, "Not enough bits to read uvlc value.");
return false;
}
literal += (1U << leading_zeros) - 1;
} else {
literal = 0;
}
*value = literal;
return true;
}
bool RawBitReader::AlignToNextByte() {
while ((bit_offset_ & 7) != 0) {
if (ReadBit() != 0) {
return false;
}
}
return true;
}
bool RawBitReader::VerifyAndSkipTrailingBits(size_t num_bits) {
if (ReadBit() != 1) return false;
for (size_t i = 0; i < num_bits - 1; ++i) {
if (ReadBit() != 0) return false;
}
return true;
}
bool RawBitReader::SkipBytes(size_t num_bytes) {
// If we are not at a byte boundary, return false.
return ((bit_offset_ & 7) != 0) ? false : SkipBits(num_bytes * 8);
}
bool RawBitReader::SkipBits(size_t num_bits) {
// If the reader is already finished, return false.
if (Finished()) return false;
// If skipping |num_bits| runs out of buffer, return false.
const size_t bit_offset = bit_offset_ + num_bits - 1;
if (DivideBy8(bit_offset, false) >= size_) return false;
bit_offset_ += num_bits;
return true;
}
bool RawBitReader::CanReadLiteral(size_t num_bits) const {
if (Finished()) return false;
const size_t bit_offset = bit_offset_ + num_bits - 1;
return DivideBy8(bit_offset, false) < size_;
}
bool RawBitReader::Finished() const {
return DivideBy8(bit_offset_, false) >= size_;
}
} // namespace libgav1
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