Add UMA stats for audio/video containers.

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::SkipBits(int num_bits) {
+  DCHECK_GE(num_bits, 0);
+
+  // Skip any bits in the current byte waiting to be processed, then
+  // process full bytes until less than 8 bits remaining.
+  while (num_bits > 0 && num_bits > num_remaining_bits_in_curr_byte_) {
+    num_bits -= num_remaining_bits_in_curr_byte_;
+    num_remaining_bits_in_curr_byte_ = 0;
+    UpdateCurrByte();

[xhwang, 2013/05/22 22:18:32]

nit: can we skip multiple bytes in one operation instead of skip one byte for
multiple times?

[jrummell, 2013/05/22 23:59:46]

I added a DLOG message to print a warning if large skips are encountered, so
that the code could be optimized.

+
+    // If there is no more data remaining, only return true if we
+    // skipped all that were requested.
+    if (num_remaining_bits_in_curr_byte_ == 0)
+      return (num_bits == 0);
+  }
+
+  // Less than 8 bits remaining to skip. Use ReadBitsInternal to verify
+  // that the remaining bits we need exist, and adjust them as necessary
+  // for subsequent operations.
+  uint64 not_needed;
+  return ReadBitsInternal(num_bits, &not_needed);
+}
+
 int BitReader::bits_available() const {
   return 8 * bytes_left_ + num_remaining_bits_in_curr_byte_;
 }
 
 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) {
@@ skipping 19 matching lines @@
     return;
 
   // Load a new byte and advance pointers.
   curr_byte_ = *data_;
   ++data_;
   --bytes_left_;
   num_remaining_bits_in_curr_byte_ = 8;
 }
 
 }  // namespace media