/// <summary>
/// Encode bits by using predefined convolutional encoding
/// </summary>
/// <param name="stream"><see cref="IBitStream"/> to encode</param>
/// <returns>Encoded <see cref="IBitStream"/></returns>
public IBitStream Encode(IBitStream stream)
{
// Since bit ratio is 1:2, there will be 2 times more encoded bits
// To save register state, we will have to encode 6 more 0-bits, resulting in 12 additional bits
var encodedStream = new Bit[2 * stream.Length + 12];
// We need to encode 6 more bits, because first 6 bits in register are 0s
var bitsToEncode = new Bit[stream.Length + 6];
for (int i = 0; i < 6; i++)
{
bitsToEncode[i] = new Bit(false);
}
// Copy 6 0-bits to the beginning of the array of bits to encode
var bits = stream.ReadAllBits();
Array.Copy(bits, 0, bitsToEncode, 6, bits.Length);
var position = 0;
var streamPosition = 0;
var bitsCount = bitsToEncode.Length;
// This piece of code does not use registers, thus we assume that we are going
// through imaginary register just by acccessing 6 bits in a row,
// and those bits are in reverse order
while (position < bitsCount)
{
// 7th bit is the 'input' bit, 6 bits before it - imaginary register
var inputBit = bitsToEncode.GetBitOrDefault(position + 6);
var secondBit = inputBit
^ bitsToEncode.GetBitOrDefault(position + 4) // reversed 2nd bit (6 - 2)
^ bitsToEncode.GetBitOrDefault(position + 1) // reversed 5th bit (6 - 5)
^ bitsToEncode.GetBitOrDefault(position); // reversed 6th bit (6 - 6)
encodedStream[streamPosition++] = inputBit;
encodedStream[streamPosition++] = secondBit;
position++;
}
return(new BitStream(encodedStream));
}
