decimal decimal::operator -=(const decimal& b)
{
if (b.isZero()) {
return *this;
}
decimal& a = *this;
const size_t w = a.length();
if (b.length() > w) {
throw underflow_error("Negative values not allowed");
}
bool borrow = false;
for (size_t i = 0; i < w; i++) {
digit d = a[i] - b[i] - (borrow ? 1 : 0);
borrow = d < 0;
a[i] = borrow ? 10 + d : d;
}
if (borrow) {
throw underflow_error("Negative values not allowed");
}
remove_lz();
return *this;
}
decimal decimal::operator +=(const decimal& b)
{
if (isZero()) {
*this = b;
return *this;
} else if (b.isZero()) {
return *this;
}
decimal& a = *this;
const size_t w = max(a.length(), b.length());
digits.resize(w + 1);
bool carry = false;
for (size_t i = 0; i < w; i++) {
digit d = a[i] + b[i] + (carry ? 1 : 0);
carry = d >= 10;
a[i] = carry ? d - 10 : d;
}
if (carry) {
a[w] = 1;
} else {
digits.resize(w);
}
return *this;
}