1 // Copyright (c) 2016 The WebM project authors. All Rights Reserved. 2 // 3 // Use of this source code is governed by a BSD-style license 4 // that can be found in the LICENSE file in the root of the source 5 // tree. An additional intellectual property rights grant can be found 6 // in the file PATENTS. All contributing project authors may 7 // be found in the AUTHORS file in the root of the source tree. 8 #include "src/var_int_parser.h" 9 10 #include <cassert> 11 #include <cstdint> 12 #include <limits> 13 14 #include "src/bit_utils.h" 15 #include "src/parser_utils.h" 16 #include "webm/reader.h" 17 #include "webm/status.h" 18 19 namespace webm { 20 21 // Spec references: 22 // http://matroska.org/technical/specs/index.html#EBML_ex 23 // https://github.com/Matroska-Org/ebml-specification/blob/master/specification.markdown#variable-size-integer Feed(Callback * callback,Reader * reader,std::uint64_t * num_bytes_read)24Status VarIntParser::Feed(Callback* callback, Reader* reader, 25 std::uint64_t* num_bytes_read) { 26 assert(callback != nullptr); 27 assert(reader != nullptr); 28 assert(num_bytes_read != nullptr); 29 assert(num_bytes_remaining_ != 0); 30 31 *num_bytes_read = 0; 32 33 if (num_bytes_remaining_ == -1) { 34 std::uint8_t first_byte; 35 const Status status = ReadByte(reader, &first_byte); 36 if (!status.completed_ok()) { 37 return status; 38 } 39 ++*num_bytes_read; 40 41 // The first byte must have a marker bit set to indicate how many octets are 42 // used. 43 if (first_byte == 0) { 44 return Status(Status::kInvalidElementValue); 45 } 46 47 total_data_bytes_ = CountLeadingZeros(first_byte); 48 num_bytes_remaining_ = total_data_bytes_; 49 50 value_ = first_byte; 51 } 52 53 std::uint64_t local_num_bytes_read; 54 const Status status = AccumulateIntegerBytes(num_bytes_remaining_, reader, 55 &value_, &local_num_bytes_read); 56 *num_bytes_read += local_num_bytes_read; 57 num_bytes_remaining_ -= static_cast<int>(local_num_bytes_read); 58 59 if (!status.completed_ok()) { 60 return status; 61 } 62 63 // Clear the marker bit. 64 constexpr std::uint64_t all_bits = std::numeric_limits<std::uint64_t>::max(); 65 const std::uint64_t data_bits = all_bits >> (57 - 7 * total_data_bytes_); 66 value_ &= data_bits; 67 68 return Status(Status::kOkCompleted); 69 } 70 71 } // namespace webm 72