1 files changed, 167 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/bitstream_reader.cc b/third_party/libwebrtc/rtc_base/bitstream_reader.cc
new file mode 100644
index 0000000000..3e1b94d8d4
--- /dev/null
+++ b/third_party/libwebrtc/rtc_base/bitstream_reader.cc
@@ -0,0 +1,167 @@
+/*
+ *  Copyright 2021 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/bitstream_reader.h"
+
+#include <stdint.h>
+
+#include <limits>
+
+#include "absl/numeric/bits.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/numerics/safe_conversions.h"
+
+namespace webrtc {
+
+uint64_t BitstreamReader::ReadBits(int bits) {
+  RTC_DCHECK_GE(bits, 0);
+  RTC_DCHECK_LE(bits, 64);
+  set_last_read_is_verified(false);
+
+  if (remaining_bits_ < bits) {
+    remaining_bits_ -= bits;
+    return 0;
+  }
+
+  int remaining_bits_in_first_byte = remaining_bits_ % 8;
+  remaining_bits_ -= bits;
+  if (bits < remaining_bits_in_first_byte) {
+    // Reading fewer bits than what's left in the current byte, just
+    // return the portion of this byte that is needed.
+    int offset = (remaining_bits_in_first_byte - bits);
+    return ((*bytes_) >> offset) & ((1 << bits) - 1);
+  }
+
+  uint64_t result = 0;
+  if (remaining_bits_in_first_byte > 0) {
+    // Read all bits that were left in the current byte and consume that byte.
+    bits -= remaining_bits_in_first_byte;
+    uint8_t mask = (1 << remaining_bits_in_first_byte) - 1;
+    result = static_cast<uint64_t>(*bytes_ & mask) << bits;
+    ++bytes_;
+  }
+
+  // Read as many full bytes as we can.
+  while (bits >= 8) {
+    bits -= 8;
+    result |= uint64_t{*bytes_} << bits;
+    ++bytes_;
+  }
+  // Whatever is left to read is smaller than a byte, so grab just the needed
+  // bits and shift them into the lowest bits.
+  if (bits > 0) {
+    result |= (*bytes_ >> (8 - bits));
+  }
+  return result;
+}
+
+int BitstreamReader::ReadBit() {
+  set_last_read_is_verified(false);
+  --remaining_bits_;
+  if (remaining_bits_ < 0) {
+    return 0;
+  }
+
+  int bit_position = remaining_bits_ % 8;
+  if (bit_position == 0) {
+    // Read the last bit from current byte and move to the next byte.
+    return (*bytes_++) & 0x01;
+  }
+
+  return (*bytes_ >> bit_position) & 0x01;
+}
+
+void BitstreamReader::ConsumeBits(int bits) {
+  RTC_DCHECK_GE(bits, 0);
+  set_last_read_is_verified(false);
+  if (remaining_bits_ < bits) {
+    Invalidate();
+    return;
+  }
+
+  int remaining_bytes = (remaining_bits_ + 7) / 8;
+  remaining_bits_ -= bits;
+  int new_remaining_bytes = (remaining_bits_ + 7) / 8;
+  bytes_ += (remaining_bytes - new_remaining_bytes);
+}
+
+uint32_t BitstreamReader::ReadNonSymmetric(uint32_t num_values) {
+  RTC_DCHECK_GT(num_values, 0);
+  RTC_DCHECK_LE(num_values, uint32_t{1} << 31);
+
+  int width = absl::bit_width(num_values);
+  uint32_t num_min_bits_values = (uint32_t{1} << width) - num_values;
+
+  uint64_t val = ReadBits(width - 1);
+  if (val < num_min_bits_values) {
+    return val;
+  }
+  return (val << 1) + ReadBit() - num_min_bits_values;
+}
+
+uint32_t BitstreamReader::ReadExponentialGolomb() {
+  // Count the number of leading 0.
+  int zero_bit_count = 0;
+  while (ReadBit() == 0) {
+    if (++zero_bit_count >= 32) {
+      // Golob value won't fit into 32 bits of the return value. Fail the parse.
+      Invalidate();
+      return 0;
+    }
+  }
+
+  // The bit count of the value is the number of zeros + 1.
+  // However the first '1' was already read above.
+  return (uint32_t{1} << zero_bit_count) +
+         rtc::dchecked_cast<uint32_t>(ReadBits(zero_bit_count)) - 1;
+}
+
+int BitstreamReader::ReadSignedExponentialGolomb() {
+  uint32_t unsigned_val = ReadExponentialGolomb();
+  if ((unsigned_val & 1) == 0) {
+    return -static_cast<int>(unsigned_val / 2);
+  } else {
+    return (unsigned_val + 1) / 2;
+  }
+}
+
+uint64_t BitstreamReader::ReadLeb128() {
+  uint64_t decoded = 0;
+  size_t i = 0;
+  uint8_t byte;
+  // A LEB128 value can in theory be arbitrarily large, but for convenience sake
+  // consider it invalid if it can't fit in an uint64_t.
+  do {
+    byte = Read<uint8_t>();
+    decoded +=
+        (static_cast<uint64_t>(byte & 0x7f) << static_cast<uint64_t>(7 * i));
+    ++i;
+  } while (i < 10 && (byte & 0x80));
+
+  // The first 9 bytes represent the first 63 bits. The tenth byte can therefore
+  // not be larger than 1 as it would overflow an uint64_t.
+  if (i == 10 && byte > 1) {
+    Invalidate();
+  }
+
+  return Ok() ? decoded : 0;
+}
+
+std::string BitstreamReader::ReadString(int num_bytes) {
+  std::string res;
+  res.reserve(num_bytes);
+  for (int i = 0; i < num_bytes; ++i) {
+    res += Read<uint8_t>();
+  }
+
+  return Ok() ? res : std::string();
+}
+
+}  // namespace webrtc