Sub(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];
int itest;
if (alead == blead)
{
itest = Digits.Compare(a, b, n - 1);
}
else
{
itest = alead < blead ? -1 : +1;
}
if (itest < 0)
{
if (blead >= mlead)
{
ValidateData(b, mod, n);
}
int carry = Digits.AddSub(a, mod, b, c, n);
Debug.Assert(carry == 0, "internal error");
}
else
{
if (alead >= mlead)
{
Debug.Assert(false, "untested code");
ValidateData(a, mod, n);
}
uint borrow = Digits.Sub(a, b, c, n);
Debug.Assert(borrow == 0, "internal error");
}
}
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");
}
}