void SubtractTimes(Bignum other, uint factor)
{
#if DEBUG
var a = new Bignum();
var b = new Bignum();
a.AssignBignum(this);
b.AssignBignum(other);
b.MultiplyByUInt32(factor);
a.SubtractBignum(b);
#endif
Debug.Assert(exponent_ <= other.exponent_);
if (factor < 3)
{
for (int i = 0; i < factor; ++i)
{
SubtractBignum(other);
}
return;
}
uint borrow = 0;
int exponent_diff = other.exponent_ - exponent_;
for (int i = 0; i < other.used_digits_; ++i)
{
ulong product = factor * other.bigits_[i];
ulong remove = borrow + product;
uint difference = bigits_[i + exponent_diff] - (uint)(remove & kBigitMask);
bigits_[i + exponent_diff] = difference & kBigitMask;
borrow = (uint)((difference >> (kChunkSize - 1)) + (remove >> kBigitSize));
}
for (int i = other.used_digits_ + exponent_diff; i < used_digits_; ++i)
{
if (borrow == 0)
{
return;
}
uint difference = bigits_[i] - borrow;
bigits_[i] = difference & kBigitMask;
borrow = difference >> (kChunkSize - 1);
}
Clamp();
#if DEBUG
Debug.Assert(Equal(a, this));
#endif
}