Add HE AAC support to ISO BMFF.

media/base/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 "media/base/bit_reader.h"
+
+namespace media {
+
+BitReader::BitReader(const uint8* data, off_t size)
+    : data_(data), bytes_left_(size), num_remaining_bits_in_curr_byte_(0) {
+  DCHECK(data_ != NULL && bytes_left_ > 0);
+
+  UpdateCurrByte();
+}
+
+BitReader::~BitReader() {}
+
+bool BitReader::ReadBitsInternal(int num_bits, uint64* out) {
+  DCHECK_LE(num_bits, 64);
+
+  *out = 0;
+
+  while (num_remaining_bits_in_curr_byte_ != 0 && num_bits != 0) {
+    int bits_to_take = std::min(num_remaining_bits_in_curr_byte_, num_bits);
+
+    *out <<= bits_to_take;
+    *out += curr_byte_ >> (num_remaining_bits_in_curr_byte_ - bits_to_take);
+    num_bits -= bits_to_take;
+    num_remaining_bits_in_curr_byte_ -= bits_to_take;
+    curr_byte_ &= (1 << num_remaining_bits_in_curr_byte_) - 1;
+
+    if (num_remaining_bits_in_curr_byte_ == 0)
+      UpdateCurrByte();
+  }
+
+  return num_bits == 0;
+}
+
+void BitReader::UpdateCurrByte() {
+  DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);
+
+  if (bytes_left_ == 0)
+    return;
+
+  // Load a new byte and advance pointers.
+  curr_byte_ = *data_;
+  ++data_;
+  --bytes_left_;
+  num_remaining_bits_in_curr_byte_ = 8;
+}
+
+}  // namespace media