| private static Square ( int w, int x ) : int[] | ||
| w | int | |
| x | int | |
| return | int[] | |
private static BigInteger ModPowBarrett(BigInteger b, BigInteger e, BigInteger m)
{
int k = m.magnitude.Length;
BigInteger mr = One.ShiftLeft((k + 1) << 5);
BigInteger yu = One.ShiftLeft(k << 6).Divide(m);
// Sliding window from MSW to LSW
int extraBits = 0, expLength = e.BitLength;
while (expLength > ExpWindowThresholds[extraBits])
{
++extraBits;
}
int numPowers = 1 << extraBits;
BigInteger[] oddPowers = new BigInteger[numPowers];
oddPowers[0] = b;
BigInteger b2 = ReduceBarrett(b.Square(), m, mr, yu);
for (int i = 1; i < numPowers; ++i)
{
oddPowers[i] = ReduceBarrett(oddPowers[i - 1].Multiply(b2), m, mr, yu);
}
int[] windowList = GetWindowList(e.magnitude, extraBits);
Debug.Assert(windowList.Length > 0);
int window = windowList[0];
int mult = window & 0xFF, lastZeroes = window >> 8;
BigInteger y;
if (mult == 1)
{
y = b2;
--lastZeroes;
}
else
{
y = oddPowers[mult >> 1];
}
int windowPos = 1;
while ((window = windowList[windowPos++]) != -1)
{
mult = window & 0xFF;
int bits = lastZeroes + BitLengthTable[mult];
for (int j = 0; j < bits; ++j)
{
y = ReduceBarrett(y.Square(), m, mr, yu);
}
y = ReduceBarrett(y.Multiply(oddPowers[mult >> 1]), m, mr, yu);
lastZeroes = window >> 8;
}
for (int i = 0; i < lastZeroes; ++i)
{
y = ReduceBarrett(y.Square(), m, mr, yu);
}
return y;
}
