Python-style integer division & modulus in C

Question

In Python and Ruby, signed integer division truncates towards negative infinity, and signed integer modulus has the same sign the second operand:

>>>         


        

Answer 1

Here is a simple implementation of floored division and modulus in C89:

#include 

div_t div_floor(int x, int y)
{
    div_t r = div(x, y);
    if (r.rem && (x < 0) != (y < 0)) {
        r.quot -= 1;
        r.rem  += y;
    }
    return r;
}

Here, div is used because it has well-defined behavior.

If you're using C++11, here is a templated implementation of floored division and modulus:

#include 

template
std::tuple div_floor(Integral x, Integral y)
{
    typedef std::tuple result_type;
    const Integral quot = x / y;
    const Integral rem  = x % y;
    if (rem && (x < 0) != (y < 0))
        return result_type(quot - 1, rem + y);
    return result_type(quot, rem);
}

In C99 and C++11, you can avoid using div since the behavior of division and modulus in C are no longer depend on the implementation.