// a += b, ignoring signal
void add_inplace(bignum& a, const bignum& b)
{
a.resize( 1 + max(a.size(), b.size()) );
b_it i;
b_cit j;
Digit carry = 0;
for (i=a.begin(), j=b.begin();
i!=a.end();
++i) {
*i += (j!=b.end() ? *j++ : 0) + carry;
if (*i >= bignum::base) {
*i -= bignum::base;
carry = 1;
} else
carry = 0;
}
assert(carry == 0);
a.clean();
}
// a -= b, ignoring signal, assume a is larger than b
void subtract_inplace(bignum& a, const bignum& b)
{
bignum x=a, y=b;
b_it i;
b_cit j;
Digit borrow = 0;
for (i=a.begin(), j=b.begin();
i!=a.end();
++i) {
*i -= (j!=b.end() ? *j++ : 0) + borrow;
if (*i < 0) {
*i += bignum::base;
borrow = 1;
} else
borrow = 0;
}
assert(borrow == 0);
a.clean();
}