xref: /dragonfly/contrib/openbsd_libm/src/ld80/s_nextafterl.c (revision 3d99825e)

/* @(#)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.
 * ====================================================
 * Copyright (c) 2002, 2003 David Schultz <das@FreeBSD.ORG>
 */

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

#include <math.h>
#include <sys/cdefs.h>

#include "math_private.h"

union IEEEl2bits {
	long double	e;
	struct {
		unsigned int	manl	:32;
		unsigned int	manh	:32;
		unsigned int	exp	:15;
		unsigned int	sign	:1;
		unsigned int	junkl	:16;
		unsigned int	junkh	:32;
	} bits;
	struct {
		unsigned long	man	:64;
		unsigned int	expsign	:16;
		unsigned long	junk	:48;
	} xbits;
};

#define	LDBL_NBIT	0x80000000
#define	mask_nbit_l(u)	((u).bits.manh &= ~LDBL_NBIT)

long double
nextafterl(long double x, long double y)
{
	volatile long double t;
	union IEEEl2bits ux, uy;

	ux.e = x;
	uy.e = y;

	if ((ux.bits.exp == 0x7fff &&
	     ((ux.bits.manh&~LDBL_NBIT)|ux.bits.manl) != 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 y;		/* x=y, return y */
	if(x==0.0) {
	    ux.bits.manh = 0;			/* return +-minsubnormal */
	    ux.bits.manl = 1;
	    ux.bits.sign = uy.bits.sign;
	    t = ux.e*ux.e;
	    if(t==ux.e) return t; else return ux.e; /* raise underflow flag */
	}
	if((x>0.0) ^ (x<y)) {			/* x -= ulp */
	    if(ux.bits.manl==0) {
		if ((ux.bits.manh&~LDBL_NBIT)==0)
		    ux.bits.exp -= 1;
		ux.bits.manh = (ux.bits.manh - 1) | (ux.bits.manh & LDBL_NBIT);
	    }
	    ux.bits.manl -= 1;
	} else {				/* x += ulp */
	    ux.bits.manl += 1;
	    if(ux.bits.manl==0) {
		ux.bits.manh = (ux.bits.manh + 1) | (ux.bits.manh & LDBL_NBIT);
		if ((ux.bits.manh&~LDBL_NBIT)==0)
		    ux.bits.exp += 1;
	    }
	}
	if(ux.bits.exp==0x7fff) return x+x;	/* overflow  */
	if(ux.bits.exp==0) {			/* underflow */
	    mask_nbit_l(ux);
	    t = ux.e * ux.e;
	    if(t!=ux.e)			/* raise underflow flag */
		return ux.e;
	}
	return ux.e;
}

__strong_reference(nextafterl, nexttowardl);