Add unittest for H264BitReader.

content/common/gpu/media/h264_bit_reader.cc

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/common/gpu/media/h264_bit_reader.h"
+#include "base/logging.h"
+
+namespace content {
+
+H264BitReader::H264BitReader()
+    : data_(NULL), bytes_left_(0), curr_byte_(0),
+      num_remaining_bits_in_curr_byte_(0), prev_two_bytes_(0) {
+}
+
+H264BitReader::~H264BitReader() {}
+
+bool H264BitReader::Initialize(const uint8* data, off_t size) {
+  DCHECK(data);
+
+  if (size < 1)
+    return false;
+
+  data_ = data;
+  bytes_left_ = size;
+  num_remaining_bits_in_curr_byte_ = 0;
+  // Initially set to 0xffff to accept all initial two-byte sequences.
+  prev_two_bytes_ = 0xffff;
+
+  return true;
+}
+
+bool H264BitReader::UpdateCurrByte() {
+  if (bytes_left_ < 1)
+    return false;
+
+  // Emulation prevention three-byte detection.
+  // If a sequence of 0x000003 is found, skip (ignore) the last byte (0x03).
+  if (*data_ == 0x03 && (prev_two_bytes_ & 0xffff) == 0) {
+    // Detected 0x000003, skip last byte.
+    ++data_;
+    --bytes_left_;
+    // Need another full three bytes before we can detect the sequence again.
+    prev_two_bytes_ = 0xffff;
+
+    if (bytes_left_ < 1)
+      return false;
+  }
+
+  // Load a new byte and advance pointers.
+  curr_byte_ = *data_++ & 0xff;
+  --bytes_left_;
+  num_remaining_bits_in_curr_byte_ = 8;
+
+  prev_two_bytes_ = (prev_two_bytes_ << 8) | curr_byte_;
+
+  return true;
+}
+
+// Read |num_bits| (1 to 31 inclusive) from the stream and return them
+// in |out|, with first bit in the stream as MSB in |out| at position
+// (|num_bits| - 1).
+bool H264BitReader::ReadBits(int num_bits, int *out) {
+  int bits_left = num_bits;
+  *out = 0;
+  DCHECK(num_bits <= 31);
+
+  while (num_remaining_bits_in_curr_byte_ < bits_left) {
+    // Take all that's left in current byte, shift to make space for the rest.
+    *out = (curr_byte_ << (bits_left - num_remaining_bits_in_curr_byte_));
+    bits_left -= num_remaining_bits_in_curr_byte_;
+
+    if (!UpdateCurrByte())
+      return false;
+  }
+
+  *out |= (curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_left));
+  *out &= ((1 << num_bits) - 1);
+  num_remaining_bits_in_curr_byte_ -= bits_left;
+
+  return true;
+}
+
+off_t H264BitReader::NumBitsLeft() {
+  return (num_remaining_bits_in_curr_byte_ + bytes_left_ * 8);
+}
+
+bool H264BitReader::HasMoreRBSPData() {
+  // Make sure we have more bits, if we are at 0 bits in current byte
+  // and updating current byte fails, we don't have more data anyway.
+  if (num_remaining_bits_in_curr_byte_ == 0 && !UpdateCurrByte())
+      return false;
+
+  // On last byte?
+  if (bytes_left_)
+    return true;
+
+  // Last byte, look for stop bit;
+  // We have more RBSP data if the last non-zero bit we find is not the
+  // first available bit.
+  return (curr_byte_ &
+          ((1 << (num_remaining_bits_in_curr_byte_ - 1)) - 1)) != 0;
+}
+
+}  // namespace content