// The whole point of the diffuser is to diffuse bits, that's why we'll pick least significant words
// with most significant word bits. This alone does some diffusion.
private static byte[] GetBigIntegerBytesWithLeastSignificantWordFirstUsing16BitMsbFirstWords(BigInteger input,
out int actualBytesWithoutPadding) {
byte[] bigEndianBytes = input.ToUnsignedBigEndianBytes();
actualBytesWithoutPadding = bigEndianBytes.Length;
bool isOddNumberOfBytes = bigEndianBytes.Length % 2 != 0;
if (isOddNumberOfBytes) {
// make sure it's even
byte[] newBigEndianBytes = new byte[bigEndianBytes.Length + 1];
// Since it's big endian, we need to shift it right by a byte and fill MSB with zeroes.
Array.Copy(bigEndianBytes, 0, newBigEndianBytes, 1, bigEndianBytes.Length);
bigEndianBytes = newBigEndianBytes;
}
byte[] result = new byte[bigEndianBytes.Length];
int ixResultByte = 0;
for (int ixWord = bigEndianBytes.Length - 2; ixWord >= 0; ixWord -= 2) {
for (int wordByteOffset = 0; wordByteOffset < 2; wordByteOffset++) {
// need to flip individual bytes
result[ixResultByte++] = bigEndianBytes[ixWord + wordByteOffset];
}
}
bool hasExtraPaddingByte = bigEndianBytes.Length != actualBytesWithoutPadding;
if (hasExtraPaddingByte) {
result[bigEndianBytes.Length - 2] = result[bigEndianBytes.Length - 1];
}
return result;
}
