nextafter.c

/*
 *                               POK header
 * 
 * The following file is a part of the POK project. Any modification should
 * made according to the POK licence. You CANNOT use this file or a part of
 * this file is this part of a file for your own project
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2009 POK team 
 *
 * Created by julien on Fri Jan 30 14:41:34 2009 
 */

/* @(#)s_nextafter.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.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH

/* IEEE functions
 *      nextafter(x,y)
 *      return the next machine floating-point number of x in the
 *      direction toward y.
 *   Special cases:
 */

#include <libm.h>
#include "math_private.h"

double
nextafter(double x, double y)
{
        int32_t hx,hy,ix,iy;
        uint32_t lx,ly;

        EXTRACT_WORDS(hx,lx,x);
        EXTRACT_WORDS(hy,ly,y);
        ix = hx&0x7fffffff;             /* |x| */
        iy = hy&0x7fffffff;             /* |y| */

        if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||   /* x is nan */
           ((iy>=0x7ff00000)&&((iy-0x7ff00000)|ly)!=0))     /* y is nan */
           return x+y;
        if(x==y) return x;              /* x=y, return x */
        if((ix|lx)==0) {                        /* x == 0 */
            INSERT_WORDS(x,hy&0x80000000,1);    /* return +-minsubnormal */
            y = x*x;
            if(y==x) return y; else return x;   /* raise underflow flag */
        }
        if(hx>=0) {                             /* x > 0 */
            if(hx>hy||((hx==hy)&&(lx>ly))) {    /* x > y, x -= ulp */
                if(lx==0) hx -= 1;
                lx -= 1;
            } else {                            /* x < y, x += ulp */
                lx += 1;
                if(lx==0) hx += 1;
            }
        } else {                                /* x < 0 */
            if(hy>=0||hx>hy||((hx==hy)&&(lx>ly))){/* x < y, x -= ulp */
                if(lx==0) hx -= 1;
                lx -= 1;
            } else {                            /* x > y, x += ulp */
                lx += 1;
                if(lx==0) hx += 1;
            }
        }
        hy = hx&0x7ff00000;
        if(hy>=0x7ff00000) return x+x;  /* overflow  */
        if(hy<0x00100000) {             /* underflow */
            y = x*x;
            if(y!=x) {          /* raise underflow flag */
                INSERT_WORDS(y,hx,lx);
                return y;
            }
        }
        INSERT_WORDS(x,hx,lx);
        return x;
}

#endif