Implement BitWriter

Change-Id: I5b7dfc2bc07227c2fe05f6de8857042bcab944c4

packager/media/base/bit_writer.cc

@@ -0,0 +1,42 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#include "packager/media/base/bit_writer.h"
+
+namespace shaka {
+namespace media {
+
+BitWriter::BitWriter(std::vector<uint8_t>* storage)
+    : storage_(storage), initial_storage_size_(storage_->size()) {}
+
+void BitWriter::WriteBits(uint32_t bits, size_t number_of_bits) {
+  DCHECK_NE(number_of_bits, 0u);
+  DCHECK_LE(number_of_bits, 32u);
+  DCHECK_LT(bits, 1ULL << number_of_bits);
+
+  num_bits_ += number_of_bits;
+  DCHECK_LE(num_bits_, 64);
+  bits_ |= static_cast<uint64_t>(bits) << (64 - num_bits_);
+
+  while (num_bits_ >= 8) {
+    storage_->push_back(bits_ >> 56);
+    bits_ <<= 8;
+    num_bits_ -= 8;
+  }
+}
+
+void BitWriter::Flush() {
+  while (num_bits_ > 0) {
+    storage_->push_back(bits_ >> 56);
+    bits_ <<= 8;
+    num_bits_ -= 8;
+  }
+  bits_ = 0;
+  num_bits_ = 0;
+}
+
+}  // namespace media
+}  // namespace shaka

packager/media/base/bit_writer.h

@@ -0,0 +1,60 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#ifndef PACKAGER_MEDIA_BASE_BIT_WRITER_H_
+#define PACKAGER_MEDIA_BASE_BIT_WRITER_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "packager/base/logging.h"
+
+namespace shaka {
+namespace media {
+
+class BitWriter {
+ public:
+  /// Constructor a BitWriter instance which writes to the provided storage.
+  /// @param storage points to vector this BitWriter writes to. Cannot be
+  ///        nullptr.
+  explicit BitWriter(std::vector<uint8_t>* storage);
+  ~BitWriter() = default;
+
+  /// Appends the sequence 'bits' of length 'number_of_bits' <= 32.
+  /// Note that 'bits' should contain at most 'number_of_bits' bits, i.e.
+  /// bits should be less than 1 << number_of_bits.
+  /// @param bits is the data to write.
+  /// @param number_of_bits is the number of LSB to write, capped at 32. Cannot
+  ///        be zero.
+  void WriteBits(uint32_t bits, size_t number_of_bits);
+
+  /// Write pending bits, and align bitstream with extra zero bits.
+  void Flush();
+
+  /// @return last written position, in bits.
+  size_t BitPos() const { return BytePos() * 8 + num_bits_; }
+
+  /// @return last written position, in bytes.
+  size_t BytePos() const { return storage_->size() - initial_storage_size_; }
+
+ private:
+  BitWriter(const BitWriter&) = delete;
+  BitWriter& operator=(const BitWriter&) = delete;
+
+  // Accumulator for unwritten bits.
+  uint64_t bits_ = 0;
+  // Number of unwritten bits.
+  int num_bits_ = 0;
+  // Buffer contains the written bits.
+  std::vector<uint8_t>* const storage_ = nullptr;
+  const size_t initial_storage_size_ = 0;
+};
+
+}  // namespace media
+}  // namespace shaka
+
+#endif  // PACKAGER_MEDIA_BASE_BIT_WRITER_H_

packager/media/base/bit_writer_unittest.cc

@@ -0,0 +1,62 @@
+// Copyright 2017 Google Inc. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+#include "packager/media/base/bit_writer.h"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+using testing::ElementsAreArray;
+
+namespace shaka {
+namespace media {
+
+TEST(BitWriterTest, Simple) {
+  std::vector<uint8_t> storage;
+  BitWriter writer(&storage);
+  writer.WriteBits(1, 1);
+  EXPECT_EQ(1u, writer.BitPos());
+  EXPECT_EQ(0u, writer.BytePos());
+  writer.Flush();
+  // Bits are byte-aligned after flush.
+  EXPECT_EQ(8u, writer.BitPos());
+  EXPECT_EQ(1u, writer.BytePos());
+
+  EXPECT_THAT(storage, ElementsAreArray({0x80}));
+}
+
+TEST(BitWriterTest, Test) {
+  std::vector<uint8_t> storage;
+  BitWriter writer(&storage);
+  writer.WriteBits(0, 1);
+  EXPECT_EQ(1u, writer.BitPos());
+  EXPECT_EQ(0u, writer.BytePos());
+  writer.WriteBits(0xab, 8);
+  EXPECT_EQ(9u, writer.BitPos());
+  EXPECT_EQ(1u, writer.BytePos());
+  writer.WriteBits(0x34, 6);
+  EXPECT_EQ(15u, writer.BitPos());
+  EXPECT_EQ(1u, writer.BytePos());
+  writer.WriteBits(0x55995599, 32);
+  EXPECT_EQ(47u, writer.BitPos());
+  EXPECT_EQ(5u, writer.BytePos());
+  writer.WriteBits(1, 1);
+  EXPECT_EQ(48u, writer.BitPos());
+  EXPECT_EQ(6u, writer.BytePos());
+  writer.WriteBits(0x13, 21);
+  EXPECT_EQ(69u, writer.BitPos());
+  EXPECT_EQ(8u, writer.BytePos());
+  writer.Flush();
+  // Bits are byte-aligned after flush.
+  EXPECT_EQ(72u, writer.BitPos());
+  EXPECT_EQ(9u, writer.BytePos());
+
+  EXPECT_THAT(storage, ElementsAreArray({0x55, 0xe8, 0xab, 0x32, 0xab, 0x33,
+                                         0x00, 0x00, 0x98}));
+}
+
+}  // namespace media
+}  // namespace shaka

packager/media/base/media_base.gyp

@@ -27,6 +27,8 @@
         'audio_timestamp_helper.h',
         'bit_reader.cc',
         'bit_reader.h',
+        'bit_writer.cc',
+        'bit_writer.h',
         'buffer_reader.cc',
         'buffer_reader.h',
         'buffer_writer.cc',
@@ -138,6 +140,7 @@
         'aes_pattern_cryptor_unittest.cc',
         'audio_timestamp_helper_unittest.cc',
         'bit_reader_unittest.cc',
+        'bit_writer_unittest.cc',
         'buffer_writer_unittest.cc',
         'closure_thread_unittest.cc',
         'container_names_unittest.cc',