System.BitConverter.ToInt32 C# (CSharp) Метод

        public static unsafe int ToInt32 (byte[]value, int startIndex) {
            if( value == null)  {
                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
            }
        
            if ((uint) startIndex >= value.Length) {
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.startIndex, ExceptionResource.ArgumentOutOfRange_Index);
            }
        
            if (startIndex > value.Length -4) {
                ThrowHelper.ThrowArgumentException(ExceptionResource.Arg_ArrayPlusOffTooSmall);
            }
        
            fixed( byte * pbyte = &value[startIndex]) {
                if( startIndex % 4 == 0) { // data is aligned 
                    return *((int *) pbyte);
                }
                else {
                    if( IsLittleEndian) { 
                        return (*pbyte) | (*(pbyte + 1) << 8)  | (*(pbyte + 2) << 16) | (*(pbyte + 3) << 24);
                    }
                    else {
                        return (*pbyte << 24) | (*(pbyte + 1) << 16)  | (*(pbyte + 2) << 8) | (*(pbyte + 3));                        
                    }
                }
            }
        }
      

        public static MidiData parse(FileStream input_file_stream)
        {
            var input_binary_reader = new BinaryReader(input_file_stream);

            HeaderChunk header_chunk;
            ushort      number_of_tracks;
            {
                var header_chunk_ID   = stringEncoder.GetString(input_binary_reader.ReadBytes(4));
                var header_chunk_size = BitConverter.ToInt32(input_binary_reader.ReadBytes(4).Reverse().ToArray <byte>(), 0);
                var header_chunk_data = input_binary_reader.ReadBytes(header_chunk_size);

                var format_type = BitConverter.ToUInt16(header_chunk_data.Take(2).Reverse().ToArray <byte>(), 0);
                number_of_tracks = BitConverter.ToUInt16(header_chunk_data.Skip(2).Take(2).Reverse().ToArray <byte>(), 0);
                var time_division = BitConverter.ToUInt16(header_chunk_data.Skip(4).Take(2).Reverse().ToArray <byte>(), 0);

                header_chunk = new HeaderChunk(format_type, time_division);
            }

            var tracks =
                Enumerable.Range(0, number_of_tracks)
                .Select(track_number =>
            {
                var track_chunk_ID   = stringEncoder.GetString(input_binary_reader.ReadBytes(4));
                var track_chunk_size = BitConverter.ToInt32(input_binary_reader.ReadBytes(4).Reverse().ToArray <byte>(), 0);
                var track_chunk_data = input_binary_reader.ReadBytes(track_chunk_size);

                return(Tuple.Create(track_chunk_size, track_chunk_data));
            }).ToList()
                .Select(raw_track => new TrackChunk(parse_events(raw_track.Item2, raw_track.Item1)));

            return(new MidiData(header_chunk, tracks));
        }