1 files changed, 224 insertions, 0 deletions
diff --git a/src/utils/raw_bit_reader.cc b/src/utils/raw_bit_reader.cc
new file mode 100644
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--- /dev/null
+++ b/src/utils/raw_bit_reader.cc
@@ -0,0 +1,224 @@
+// 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