//windowed naf form of BigInt k, w is the window size
sbyte[] Naf(BigInt k, byte w)
{
// The window NAF is at most 1 element longer than the binary
// representation of the integer k. byte can be used instead of short or
// int unless the window width is larger than 8. For larger width use
// short or int. However, a width of more than 8 is not efficient for
// m = log2(q) smaller than 2305 Bits. Note: Values for m larger than
// 1000 Bits are currently not used in practice.
sbyte[] wnaf = new sbyte[k.BitLength() + 1];
// 2^width as short and BigInteger
short pow2wB = (short)(1 << w);
BigInt pow2wBI = BigInt.ValueOf(pow2wB);
int i = 0;
// The actual length of the WNAF
int length = 0;
// while k >= 1
while (k.Signum() > 0)
{
// if k is odd
if (k.TestBit(0))
{
// k mod 2^width
BigInt remainder = k.Mod(pow2wBI);
// if remainder > 2^(width - 1) - 1
if (remainder.TestBit(w - 1))
{
wnaf[i] = (sbyte)(remainder.IntValue() - pow2wB);
}
else
{
wnaf[i] = (sbyte)remainder.IntValue();
}
// wnaf[i] is now in [-2^(width-1), 2^(width-1)-1]
k = k.Subtract(BigInt.ValueOf(wnaf[i]));
length = i;
}
else
{
wnaf[i] = 0;
}
// k = k/2
k = k.ShiftRight(1);
i++;
}
length++;
// Reduce the WNAF array to its actual length
sbyte[] wnafShort = new sbyte[length];
Array.Copy(wnaf, 0, wnafShort, 0, length);
return(wnafShort);
}
//multiplication using Jacobian coordinates
public JacobPoint JMultiplyMut(Point p, BigInt k)
{
if (!(this.field.IsValidElement(p.X)) || !(this.field.IsValidElement(p.Y)))
{
throw new ArgumentException("The input point must be taken over the field.");
}
if (p.IsInfinity())
{
return(this.AToJ(p));
}
if (k.Equals(BigInt.ZERO))
{
return(JacobPoint.INFINITY);
}
if (k.Equals(BigInt.ONE))
{
return(this.AToJ(p));
}
if (k.Signum() == -1)
{
k = k.Abs();
p = this.Negate(p);
}
//byte [] ba =k.toByteArray();
int degree = k.BitLength() - 2;
JacobPoint result = this.AToJ(p);
for (int i = degree; i >= 0; i--)
{
this.JDblMut(result);
if (k.TestBit(i)) ///AQUI TE QUEDASTE IMPLEMENTAR TESTBIT
{
this.JAddMut(result, p);
}
}
return(result);
}
public void BitLengthTest()
{
BigInt a = new BigInt(123456);
Assert.AreEqual(17, a.BitLength());
}