s_modf.c

/* @(#)s_modf.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/*
 * modf(double x, double *iptr) 
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *      Bit twiddling.
 *
 * Exception:
 *      No exception.
 */

#include "fdlibm.h"

static const double one = 1.0;

double modf(double x, double *iptr)
{
        int i0,i1,j0;
        unsigned i;
        __getHI(i0,x);          /* high x */
        __getLO(i1,x);          /* low  x */
        j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
        if(j0<20) {                     /* integer part in high x */
            if(j0<0) {                  /* |x|<1 */
                __setHILO(*iptr, i0&0x80000000U, 0);              /* *iptr = +-0 */
                return x;
            } else {
                i = (0x000fffff)>>j0;
                if(((i0&i)|i1)==0) {            /* x is integral */
                    *iptr = x;
                    __setHILO(x, i0 & 0x80000000U , 0);      /* return +-0 */
                    return x;
                } else {
                    __setHILO(*iptr, i0&(~i), 0);
                    return x - *iptr;
                }
            }
        } else if (j0>51) {             /* no fraction part */
            *iptr = x*one;
            __setHILO(x, i0 & 0x80000000U , 0);      /* return +-0 */
            return x;
        } else {                        /* fraction part in low x */
            i = ((unsigned)(0xffffffff))>>(j0-20);
            if((i1&i)==0) {             /* x is integral */
                *iptr = x;
                __setHILO(x, i0 & 0x80000000U , 0);  /* return +-0 */
                return x;
            } else {
                __setHILO(*iptr, i0, i1&(~i));
                return x - *iptr;
            }
        }
}