source: vendor/python/2.5/Python/fmod.c

/* Portable fmod(x, y) implementation for systems that don't have it */

#include "pyconfig.h"

#include "pyport.h"
#include <errno.h>

double
fmod(double x, double y)
{
        double i, f;
        
        if (y == 0.0) {
                errno = EDOM;
                return 0.0;
        }
        
        /* return f such that x = i*y + f for some integer i
           such that |f| < |y| and f has the same sign as x */
        
        i = floor(x/y);
        f = x - i*y;
        if ((x < 0.0) != (y < 0.0))
                f = f-y;
        return f;
}