// As described on page 8 of RFC 8554
private BigInteger Coef(BitString S, int i, int w)
{
var resultlhs = new BitString(new BigInteger((1 << w) - 1));
var resultrhs = new BitString(S.MSBSubstring(i * w / 8 * 8, 8).ToPositiveBigInteger() >> (8 - (w * (i % (8 / w)) + w)));
return(resultlhs.AND(resultrhs).ToPositiveBigInteger());
}
public static BitString Encode(EdPoint point, int b)
{
var encoding = new BitString(point.Y, b);
var xBit = new BitString(point.X, b).GetLeastSignificantBits(1);
var bytes = new byte[b / 8];
bytes[0] = 1 << 7;
if (xBit.Equals(BitString.One()))
{
encoding = encoding.OR(new BitString(bytes));
}
else
{
encoding = encoding.AND(new BitString(bytes).NOT());
}
return(BitString.ReverseByteOrder(encoding)); // switch to little endian
}
