Split the bit reader functionalities from the byte stream provider.

media/base/bit_reader_base.cc

+// Copyright (c) 2013 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_base.h"
+
+#include <base/sys_byteorder.h>
+
+namespace media {
+
+BitReaderBase::BitReaderBase()
+    : nbits_(0),
+      reg_(0),
+      nbits_next_(0),
+      reg_next_(0) {
+}
+
+BitReaderBase::~BitReaderBase() {
+}
+
+bool BitReaderBase::ReadFlag(bool* flag) {
+  if (nbits_ == 0) {
+    if (!Refill(1))

[damienv1, 2013/12/19 03:29:12]

Could be only one condition.

[damienv1, 2013/12/19 21:46:34]

Done.

+      return false;
+  }
+
+  *flag = (static_cast<int64>(reg_) < 0);
+  reg_ <<= 1;
+  nbits_--;
+  return true;
+
+}
+
+bool BitReaderBase::ReadUE(uint32* out) {
+  // Get the number of leading zeros.
+  int zero_count = -1;
+  bool is_one;
+  do {
+    if (nbits_ == 0 && !Refill(1))
+      return false;
+    is_one = (static_cast<int64>(reg_) < 0);
+    reg_ <<= 1;
+    nbits_--;

[damienv1, 2013/12/19 03:46:51]

zero_count++;

[damienv1, 2013/12/19 21:46:34]

Done.

+  } while(!is_one);
+
+  // If zero_count is greater than 31, the calculated value will overflow.
+  if (zero_count > 31)
+    return false;
+
+  // Read the actual value.
+  uint32 base = (1 << zero_count) - 1;
+  uint32 offset;
+  if (!ReadBits(zero_count, &offset))
+    return false;
+  *out = base + offset;
+
+  return true;
+}
+
+bool BitReaderBase::SkipBits(int num_bits) {
+  DCHECK_GE(num_bits, 0);
+  DVLOG_IF(0, num_bits > 100)
+      << "BitReader::SkipBits inefficient for large skips";
+
+  uint64 dummy;
+  while (num_bits >= 32) {
+    if (!ReadBitsInternal(32, &dummy))
+      return false;
+    num_bits -= 32;
+  }
+
+  if (num_bits > 0)
+    return ReadBitsInternal(num_bits, &dummy);
+
+  return true;
+}
+
+int BitReaderBase::bits_available_in_registers() const {
+  return nbits_ + nbits_next_;
+}
+
+bool BitReaderBase::ReadBitsInternal(int num_bits, uint64* out) {
+  DCHECK_GE(num_bits, 0);
+
+  if (num_bits == 0) {
+    *out = 0;
+    return true;
+  }
+
+  if (num_bits > nbits_) {
+    if (!Refill(num_bits)) {

[damienv1, 2013/12/19 03:29:12]

Could be only one condition.

[damienv1, 2013/12/19 21:46:34]

Done.

+      ResetRegisters();
+      return false;
+    }
+  }
+
+  *out = reg_ >> (sizeof(RegType) * CHAR_BIT - num_bits);
+  reg_ <<= num_bits;
+  nbits_ -= num_bits;
+  return true;
+}
+
+bool BitReaderBase::Refill(int min_nbits) {
+  DCHECK_LE(min_nbits, static_cast<int>(sizeof(RegType) * CHAR_BIT));
+
+  // Transfer from the next to the current register.
+  RefillCurrentRegister();
+  if (min_nbits <= nbits_)
+    return true;
+  DCHECK_EQ(nbits_next_, 0);
+
+  // Strict minimum number of bytes to refill.
+  int min_nbytes = (min_nbits - nbits_ + CHAR_BIT - 1) / CHAR_BIT;
+
+  // Max number of bytes to refill.
+  int max_nbytes = 8;

[damienv1, 2013/12/19 02:01:25]

Should be sizeof(RegType)

[damienv1, 2013/12/19 21:46:34]

Done.

+
+  // Refill.
+  const uint8* byte_stream_window;
+  int window_size = GetBytes(min_nbytes, max_nbytes, &byte_stream_window);
+  if (window_size < min_nbytes)
+    return false;
+
+  reg_next_ = 0;
+  memcpy(&reg_next_, byte_stream_window, window_size);
+  reg_next_ = base::ByteSwap(reg_next_);

[damienv1, 2013/12/19 03:29:12]

Should be NetToHost64 !

[damienv1, 2013/12/19 21:46:34]

Done.

+  nbits_next_ = window_size * CHAR_BIT;
+
+  // Transfer from the next to the current register.
+  RefillCurrentRegister();
+  DCHECK_LE(min_nbits, nbits_);
+
+  return true;
+}
+
+void BitReaderBase::RefillCurrentRegister() {
+  if (nbits_ == 64 || nbits_next_ == 0)

[damienv1, 2013/12/19 02:01:25]

Should be sizeof(RegType) * CHAR_BIT

[damienv1, 2013/12/19 21:46:34]

Done.

+    return;
+
+  reg_ |= (reg_next_ >> nbits_);
+
+  int free_nbits = static_cast<int>(sizeof(RegType) * CHAR_BIT) - nbits_;
+  if (free_nbits >= nbits_next_) {
+    nbits_ += nbits_next_;
+    reg_next_ = 0;
+    nbits_next_ = 0;
+  } else {
+    nbits_ += free_nbits;
+    reg_next_ <<= free_nbits;
+    nbits_next_ -= free_nbits;
+  }
+}
+
+void BitReaderBase::ResetRegisters() {
+  reg_ = 0;
+  nbits_ = 0;
+  reg_next_ = 0;
+  nbits_next_ = 0;
+}
+
+}  // namespace media