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; }