// Full multiplication.
// For every digit d in 'a' b is multiplied by d.
// Final result is obtained by addition of all results of multiplications with proper offset.
digit* multiply(const digit* a, const digit* b)
{
digit* result = 0;
int offset = 0;
while(a)
{
if(a->n != i2d(0))
{
digit* row = copy(b);
multiply_by_digit(row, d2i(a->n));
for(int i = 0; i < offset; ++i)
{
digit* new_row = new digit;
new_row->next = row;
new_row->n = i2d(0);
row = new_row;
}
addto(row, result);
deletebigint(row);
}
++offset;
a = a->next;
}
// needed when a or b is 0
rm_leading_0s(result);
return result;
}
BigInt::reference BigInt::operator*= ( const_reference o )
{
if ( o.buffer.size() == 1 )
return multiply_by_digit ( o.buffer[0] );
sign_ = sign_ != o.sign_;
std::queue<BigInt> partial;
for ( unsigned i = 0; i < o.buffer.size(); i++ )
{
BigInt copy = *this;
copy.multiply_by_digit ( o.buffer[i] );
partial.push ( copy );
}
BigInt temp;
*this = zero;
for( unsigned i = 0; !partial.empty(); i++ )
{
temp = partial.front();
partial.pop();
temp.buffer = buffer_type(i,0) + temp.buffer;
*this += temp;
}
return normalize();
}
