#include <math.h>

double fmax(double x, double y)
{
        if (isnan(x))
                return y;
        if (isnan(y))
                return x;
        /* handle signed zeros, see C99 Annex F.9.9.2 */
        if (signbit(x) != signbit(y))
                return signbit(x) ? y : x;
        return x < y ? y : x;
}