adtools/clib2

/*
 * $Id: math_nextafter.c,v 1.2 2006-01-08 12:04:24 obarthel Exp $
 *
 * :ts=4
 *
 * Portable ISO 'C' (1994) runtime library for the Amiga computer
 * Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Neither the name of Olaf Barthel nor the names of contributors
 *     may be used to endorse or promote products derived from this
 *     software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * PowerPC math library based in part on work by Sun Microsystems
 * 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 _MATH_HEADERS_H
#include "math_headers.h"
#endif /* _MATH_HEADERS_H */

/****************************************************************************/

#if defined(FLOATING_POINT_SUPPORT)

/****************************************************************************/

double
nextafter(double x,double y)
{
    long hx,hy,ix,iy;
    unsigned long 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&0x80000000U,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 /* FLOATING_POINT_SUPPORT */