Repo created

TMessagesProj/jni/voip/webrtc/rtc_base/bit_buffer.cc

@@ -0,0 +1,230 @@
+/*
+ *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/bit_buffer.h"
+
+#include <algorithm>
+#include <limits>
+
+#include "absl/numeric/bits.h"
+#include "absl/strings/string_view.h"
+#include "rtc_base/checks.h"
+
+namespace {
+
+// Returns the highest byte of `val` in a uint8_t.
+uint8_t HighestByte(uint64_t val) {
+  return static_cast<uint8_t>(val >> 56);
+}
+
+// Returns the result of writing partial data from `source`, of
+// `source_bit_count` size in the highest bits, to `target` at
+// `target_bit_offset` from the highest bit.
+uint8_t WritePartialByte(uint8_t source,
+                         size_t source_bit_count,
+                         uint8_t target,
+                         size_t target_bit_offset) {
+  RTC_DCHECK(target_bit_offset < 8);
+  RTC_DCHECK(source_bit_count < 9);
+  RTC_DCHECK(source_bit_count <= (8 - target_bit_offset));
+  // Generate a mask for just the bits we're going to overwrite, so:
+  uint8_t mask =
+      // The number of bits we want, in the most significant bits...
+      static_cast<uint8_t>(0xFF << (8 - source_bit_count))
+      // ...shifted over to the target offset from the most signficant bit.
+      >> target_bit_offset;
+
+  // We want the target, with the bits we'll overwrite masked off, or'ed with
+  // the bits from the source we want.
+  return (target & ~mask) | (source >> target_bit_offset);
+}
+
+}  // namespace
+
+namespace rtc {
+
+BitBufferWriter::BitBufferWriter(uint8_t* bytes, size_t byte_count)
+    : writable_bytes_(bytes),
+      byte_count_(byte_count),
+      byte_offset_(),
+      bit_offset_() {
+  RTC_DCHECK(static_cast<uint64_t>(byte_count_) <=
+             std::numeric_limits<uint32_t>::max());
+}
+
+uint64_t BitBufferWriter::RemainingBitCount() const {
+  return (static_cast<uint64_t>(byte_count_) - byte_offset_) * 8 - bit_offset_;
+}
+
+bool BitBufferWriter::ConsumeBytes(size_t byte_count) {
+  return ConsumeBits(byte_count * 8);
+}
+
+bool BitBufferWriter::ConsumeBits(size_t bit_count) {
+  if (bit_count > RemainingBitCount()) {
+    return false;
+  }
+
+  byte_offset_ += (bit_offset_ + bit_count) / 8;
+  bit_offset_ = (bit_offset_ + bit_count) % 8;
+  return true;
+}
+
+void BitBufferWriter::GetCurrentOffset(size_t* out_byte_offset,
+                                       size_t* out_bit_offset) {
+  RTC_CHECK(out_byte_offset != nullptr);
+  RTC_CHECK(out_bit_offset != nullptr);
+  *out_byte_offset = byte_offset_;
+  *out_bit_offset = bit_offset_;
+}
+
+bool BitBufferWriter::Seek(size_t byte_offset, size_t bit_offset) {
+  if (byte_offset > byte_count_ || bit_offset > 7 ||
+      (byte_offset == byte_count_ && bit_offset > 0)) {
+    return false;
+  }
+  byte_offset_ = byte_offset;
+  bit_offset_ = bit_offset;
+  return true;
+}
+
+bool BitBufferWriter::WriteUInt8(uint8_t val) {
+  return WriteBits(val, sizeof(uint8_t) * 8);
+}
+
+bool BitBufferWriter::WriteUInt16(uint16_t val) {
+  return WriteBits(val, sizeof(uint16_t) * 8);
+}
+
+bool BitBufferWriter::WriteUInt32(uint32_t val) {
+  return WriteBits(val, sizeof(uint32_t) * 8);
+}
+
+bool BitBufferWriter::WriteBits(uint64_t val, size_t bit_count) {
+  if (bit_count > RemainingBitCount()) {
+    return false;
+  }
+  size_t total_bits = bit_count;
+
+  // For simplicity, push the bits we want to read from val to the highest bits.
+  val <<= (sizeof(uint64_t) * 8 - bit_count);
+
+  uint8_t* bytes = writable_bytes_ + byte_offset_;
+
+  // The first byte is relatively special; the bit offset to write to may put us
+  // in the middle of the byte, and the total bit count to write may require we
+  // save the bits at the end of the byte.
+  size_t remaining_bits_in_current_byte = 8 - bit_offset_;
+  size_t bits_in_first_byte =
+      std::min(bit_count, remaining_bits_in_current_byte);
+  *bytes = WritePartialByte(HighestByte(val), bits_in_first_byte, *bytes,
+                            bit_offset_);
+  if (bit_count <= remaining_bits_in_current_byte) {
+    // Nothing left to write, so quit early.
+    return ConsumeBits(total_bits);
+  }
+
+  // Subtract what we've written from the bit count, shift it off the value, and
+  // write the remaining full bytes.
+  val <<= bits_in_first_byte;
+  bytes++;
+  bit_count -= bits_in_first_byte;
+  while (bit_count >= 8) {
+    *bytes++ = HighestByte(val);
+    val <<= 8;
+    bit_count -= 8;
+  }
+
+  // Last byte may also be partial, so write the remaining bits from the top of
+  // val.
+  if (bit_count > 0) {
+    *bytes = WritePartialByte(HighestByte(val), bit_count, *bytes, 0);
+  }
+
+  // All done! Consume the bits we've written.
+  return ConsumeBits(total_bits);
+}
+
+bool BitBufferWriter::WriteNonSymmetric(uint32_t val, uint32_t num_values) {
+  RTC_DCHECK_LT(val, num_values);
+  RTC_DCHECK_LE(num_values, uint32_t{1} << 31);
+  if (num_values == 1) {
+    // When there is only one possible value, it requires zero bits to store it.
+    // But WriteBits doesn't support writing zero bits.
+    return true;
+  }
+  size_t count_bits = absl::bit_width(num_values);
+  uint32_t num_min_bits_values = (uint32_t{1} << count_bits) - num_values;
+
+  return val < num_min_bits_values
+             ? WriteBits(val, count_bits - 1)
+             : WriteBits(val + num_min_bits_values, count_bits);
+}
+
+size_t BitBufferWriter::SizeNonSymmetricBits(uint32_t val,
+                                             uint32_t num_values) {
+  RTC_DCHECK_LT(val, num_values);
+  RTC_DCHECK_LE(num_values, uint32_t{1} << 31);
+  size_t count_bits = absl::bit_width(num_values);
+  uint32_t num_min_bits_values = (uint32_t{1} << count_bits) - num_values;
+
+  return val < num_min_bits_values ? (count_bits - 1) : count_bits;
+}
+
+bool BitBufferWriter::WriteExponentialGolomb(uint32_t val) {
+  // We don't support reading UINT32_MAX, because it doesn't fit in a uint32_t
+  // when encoded, so don't support writing it either.
+  if (val == std::numeric_limits<uint32_t>::max()) {
+    return false;
+  }
+  uint64_t val_to_encode = static_cast<uint64_t>(val) + 1;
+
+  // We need to write bit_width(val+1) 0s and then val+1. Since val (as a
+  // uint64_t) has leading zeros, we can just write the total golomb encoded
+  // size worth of bits, knowing the value will appear last.
+  return WriteBits(val_to_encode, absl::bit_width(val_to_encode) * 2 - 1);
+}
+
+bool BitBufferWriter::WriteSignedExponentialGolomb(int32_t val) {
+  if (val == 0) {
+    return WriteExponentialGolomb(0);
+  } else if (val > 0) {
+    uint32_t signed_val = val;
+    return WriteExponentialGolomb((signed_val * 2) - 1);
+  } else {
+    if (val == std::numeric_limits<int32_t>::min())
+      return false;  // Not supported, would cause overflow.
+    uint32_t signed_val = -val;
+    return WriteExponentialGolomb(signed_val * 2);
+  }
+}
+
+bool BitBufferWriter::WriteLeb128(uint64_t val) {
+  bool success = true;
+  do {
+    uint8_t byte = static_cast<uint8_t>(val & 0x7f);
+    val >>= 7;
+    if (val > 0) {
+      byte |= 0x80;
+    }
+    success &= WriteUInt8(byte);
+  } while (val > 0);
+  return success;
+}
+
+bool BitBufferWriter::WriteString(absl::string_view data) {
+  bool success = true;
+  for (char c : data) {
+    success &= WriteUInt8(c);
+  }
+  return success;
+}
+
+}  // namespace rtc