Simplest way to check if two integers have same sign?

Question

Which is the simplest way to check if two integers have same sign? Is there any short bitwise trick to do this?

Answer 1

Here is a version that works in C/C++ that doesn't rely on integer sizes or have the overflow problem (i.e. x*y>=0 doesn't work)

bool SameSign(int x, int y)
{
    return (x >= 0) ^ (y < 0);
}

Of course, you can geek out and template:

template 
bool SameSign(typename valueType x, typename valueType y)
{
    return (x >= 0) ^ (y < 0);
}

Note: Since we are using exclusive or, we want the LHS and the RHS to be different when the signs are the same, thus the different check against zero.