source: vendor/FreeBSD-msun/current/src/s_nexttoward.c

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

#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_nexttoward.c,v 1.1 2005/03/07 04:56:46 das Exp $";
#endif

/*
 * We assume that a long double has a 15-bit exponent.  On systems
 * where long double is the same as double, nexttoward() is an alias
 * for nextafter(), so we don't use this routine.
 */

#include <float.h>

#include "fpmath.h"
#include "math.h"
#include "math_private.h"

#if LDBL_MAX_EXP != 0x4000
#error "Unsupported long double format"
#endif

double
nexttoward(double x, long double y)
{
        union IEEEl2bits uy;
        volatile double t;
        int32_t hx,ix;
        u_int32_t lx;

        EXTRACT_WORDS(hx,lx,x);
        ix = hx&0x7fffffff;             /* |x| */
        uy.e = y;

        if(((ix>=0x7ff00000)&&((ix-0x7ff00000)|lx)!=0) ||
            (uy.bits.exp == 0x7fff &&
             ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0))
           return x+y;  /* x or y is nan */
        if(x==y) return (double)y;              /* x=y, return y */
        if(x==0.0) {
            INSERT_WORDS(x,uy.bits.sign<<31,1); /* return +-minsubnormal */
            t = x*x;
            if(t==x) return t; else return x;   /* raise underflow flag */
        }
        if(hx>0.0 ^ x < y) {                    /* x -= ulp */
            if(lx==0) hx -= 1;
            lx -= 1;
        } else {                                /* x += ulp */
            lx += 1;
            if(lx==0) hx += 1;
        }
        ix = hx&0x7ff00000;
        if(ix>=0x7ff00000) return x+x;  /* overflow  */
        if(ix<0x00100000) {             /* underflow */
            t = x*x;
            if(t!=x) {          /* raise underflow flag */
                INSERT_WORDS(y,hx,lx);
                return y;
            }
        }
        INSERT_WORDS(x,hx,lx);
        return x;
}