Add HE AAC support to ISO BMFF.

media/base/bit_reader.cc

Index: media/base/bit_reader.cc
diff --git a/media/base/bit_reader.cc b/media/base/bit_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..709d5ae87c59d47148ffb630666d98778a540c7c
--- /dev/null
+++ b/media/base/bit_reader.cc
@@ -0,0 +1,53 @@
+// 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) {

[acolwell GONE FROM CHROMIUM, 2012/07/17 22:38:21]

nit: off_t -> int here and on bytes_left_

+  DCHECK(data != NULL || size == 0);  // Data cannot be NULL if size is not 0.

[Ami GONE FROM CHROMIUM, 2012/07/17 23:22:18]

Comment isn't adding value.

[Ami GONE FROM CHROMIUM, 2012/07/17 23:22:18]

What's the value of supporting empty buffers?
I suspect all your callers could more profitably simply never create the
bitreader if the buffer is empty.

[xiaomings, 2012/07/19 00:16:32]

Done.

[xiaomings, 2012/07/19 00:16:32]

Done.

+
+  data_ = data;
+  bytes_left_ = size;
+  num_remaining_bits_in_curr_byte_ = 0;

[Ami GONE FROM CHROMIUM, 2012/07/17 23:22:18]

These three assignments belong in an initializer list

[xiaomings, 2012/07/19 00:16:32]

Done.

+
+  UpdateCurrByte();
+}
+
+BitReader::~BitReader() {}
+
+void BitReader::UpdateCurrByte() {
+  DCHECK_EQ(num_remaining_bits_in_curr_byte_, 0);
+
+  if (bytes_left_ < 1)

[Ami GONE FROM CHROMIUM, 2012/07/17 23:22:18]

Can this ever be negative?  Why not ==0 for clarity?

[xiaomings, 2012/07/19 00:16:32]

Done.

+    return;
+
+  // Load a new byte and advance pointers.
+  curr_byte_ = *data_;
+  ++data_;
+  --bytes_left_;
+  num_remaining_bits_in_curr_byte_ = 8;
+}
+
+bool BitReader::SkipBits(int num_bits) {
+  int dummy;
+  const int kDummySize = static_cast<int>(sizeof(dummy)) * 8;
+
+  while (num_bits > kDummySize) {
+    if (ReadBits(kDummySize, &dummy)) {
+      num_bits -= kDummySize;
+    } else {
+      return false;
+    }
+  }
+
+  return ReadBits(num_bits, &dummy);
+}
+
+off_t BitReader::NumBitsLeft() const {
+  return (num_remaining_bits_in_curr_byte_ + bytes_left_ * 8);
+}
+
+}  // namespace media