private void Reduce(MutableInteger z)
{
// var qhat = (z >> (bLength * (k - 1))) * mu >> (bLength * (k + 1));
var reg1 = store.Allocate().Set(z);
reg1.RightShift(bToTheKMinusOneLength);
#if false
var reg2.store.Allocate().SetProductShifted(reg1, muRep, bToTheKPlusOneLength);
#else
var reg2 = store.Allocate().SetProduct(reg1, muRep);
reg2.RightShift(bToTheKPlusOneLength);
#endif
// var r = z % bToTheKPlusOne - qhat * p % bToTheKPlusOne;
z.Mask(bToTheKPlusOneLength);
#if true
reg1.SetProductMasked(reg2, pRep, bToTheKPlusOneLength);
#else
reg1.SetProduct(reg2, pRep);
reg1.Mask(bToTheKPlusOneLength);
#endif
// if (r.Sign == -1) r += bToTheKPlusOne;
if (z < reg1)
{
z.SetBit(bToTheKPlusOneLength, true);
}
z.Subtract(reg1);
// while (r >= p) r -= p;
while (z >= pRep)
{
z.Subtract(pRep);
}
store.Release(reg1);
store.Release(reg2);
}
public static MutableInteger SetModularInversePowerOfTwoModulus(this MutableInteger c, MutableInteger d, int n, MutableIntegerStore store)
{
// See 9.2 in: http://gmplib.org/~tege/divcnst-pldi94.pdf
c.Set(d);
var two = store.Allocate().Set(2);
var reg1 = store.Allocate();
var reg2 = store.Allocate();
for (int m = 3; m < n; m *= 2)
{
reg1.Set(c);
reg2.SetProduct(reg1, d);
reg2.Mask(n);
reg2.SetDifference(two, reg2);
c.SetProduct(reg1, reg2);
c.Mask(n);
}
if (c.Sign == -1)
{
c.Add(reg1.Set(1).LeftShift(n));
}
store.Release(two);
store.Release(reg1);
store.Release(reg2);
return(c);
}
