Add(Digits a, Digits b, Digits c, Digits mod, int n)
{
Debug.Assert(n != 0, "internal error");
Digit alead = a[n - 1], blead = b[n - 1], mlead = mod[n - 1];
if (alead >= mlead)
{
ValidateData(a, mod, n);
}
if (blead >= mlead)
{
ValidateData(b, mod, n);
}
int test;
if (blead > mlead - alead)
{
test = +1;
}
else if (mlead - alead - blead > 1)
{
test = -1;
}
else
{
test = Digits.CompareSum(a, b, mod, n);
}
if (test >= 0)
{
int carry = Digits.AddSub(a, b, mod, c, n);
Debug.Assert(carry == 0, "internal error");
}
else
{
uint carry = Digits.Add(a, b, c, n);
Debug.Assert(carry == 0, "internal error");
}
}
internal Modulus(Digits mod, int digitN, bool fromRight)
{
if (digitN == 0 || mod[digitN - 1] == 0)
{
throw new ArgumentException();
}
_mod = mod;
_digitN = digitN;
_fromRight = fromRight;
_one = new Digits(digitN);
_multiplier1 = new Digits(digitN);
_multiplier2 = new Digits(digitN);
// this.mod.Set(this.mod, _digitN);
_leftRecip = new Reciprocal();
Digits.DivPrecondition(mod, digitN, _leftRecip);
Digit mod0inv = 0;
if ((mod[0] & 1) != 0)
{
mod0inv = Digit.TwoAdicInverse(mod[0]);
}
_rightRecip = mod0inv;
int digitN2 = (digitN + 1) / 2;
Digits temp = new Digits(digitN + digitN2);
if (!fromRight)
{
_algorithm = new MulAlgorithm(_MulFromLeft);
int dividendN = digitN + digitN2;
_scaleBitN = 0;
for (int i = 0; i != dividendN; i++)
{
temp[i] = Digit.MaxValue;
}
temp[dividendN - 1] = Digit.MaxValue >> _leftRecip._shiftBitN;
Digits q = new Digits(digitN2 + 1);
Digits r = new Digits(digitN);
Digits.Div(temp, dividendN, mod, digitN, _leftRecip, q, r);
Debug.Assert(q[digitN2] == 1, "internal error");
Digits.Add(r, 1U, r, digitN);
Digits.Sub(mod, r, r, digitN);
}
else
{
_algorithm = new MulAlgorithm(_MulFromRight);
_scaleBitN = Digit.BitN * digitN;
if (mod0inv == 0)
{
throw new ArgumentException();
}
_multiplier2[0] = mod0inv;
temp[digitN] = Digits.Mul(mod, mod0inv, temp, digitN);
Debug.Assert(temp[0] == 1, "internal error");
for (int i = 1; i != digitN2; i++)
{
Digit mul = unchecked (0 - mod0inv * temp[i]);
_multiplier2[i] = mul;
temp[i + digitN]
= Digits.Accumulate(mod, mul, temp + i, digitN);
Debug.Assert(temp[i] == 0, "internal error");
}
_multiplier1._Set(temp + digitN2, digitN);
}
_ToModular(new Digits(new Digit[] { 1 }), 1, _one);
}