source: trunk/sys/libm/s_isnan.c @ 143

/* @(#)s_isnan.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
 * isnan(x) returns 1 is x is nan, else 0;
 * no branching!
 */

#include <libm/fdlibm.h>

#ifdef __STDC__
static const double one = 1.0;
#else
static double one = 1.0;
#endif

#ifdef __STDC__
        int isnan(double x)
#else
        int isnan(x)
        double x;
#endif
{
        int n0,hx,lx;
        n0 = ((*(int*)&one)>>29)^1;
        hx = (*(n0+(int*)&x)&0x7fffffff);
        lx = *(1-n0+(int*)&x);
        hx |= (unsigned)(lx|(-lx))>>31; 
        hx = 0x7ff00000 - hx;
        return ((unsigned)(hx))>>31;
}