s_nextafterl.c revision 1.3 
1/*	$NetBSD: s_nextafterl.c,v 1.3 2013/02/14 08:56:56 matt Exp $	*/
2
3/* @(#)s_nextafter.c 5.1 93/09/24 */
4/*
5 * ====================================================
6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 *
8 * Developed at SunPro, a Sun Microsystems, Inc. business.
9 * Permission to use, copy, modify, and distribute this
10 * software is freely granted, provided that this notice
11 * is preserved.
12 * ====================================================
13 */
14
15#include <sys/cdefs.h>
16__RCSID("$NetBSD: s_nextafterl.c,v 1.3 2013/02/14 08:56:56 matt Exp $");
17
18#include <float.h>
19#include <math.h>
20#include <machine/ieee.h>
21
22#ifdef EXT_EXP_INFNAN
23#if LDBL_MAX_EXP != 0x4000
24#error "Unsupported long double format"
25#endif
26
27#ifdef LDBL_IMPLICIT_NBIT
28#define	LDBL_NBIT	0
29#endif
30
31/*
32 * IEEE functions
33 *      nextafterl(x,y)
34 *      return the next machine floating-point number of x in the
35 *      direction toward y.
36 *   Special cases:
37 *	If x == y, y shall be returned
38 *	If x or y is NaN, a NaN shall be returned
39 */
40long double
41nextafterl(long double x, long double y)
42{
43	volatile long double t;
44	union ieee_ext_u ux, uy;
45
46	ux.extu_ld = x;
47	uy.extu_ld = y;
48
49	if ((ux.extu_exp == EXT_EXP_NAN &&
50		((ux.extu_frach &~ LDBL_NBIT)|ux.extu_fracl) != 0) ||
51	    (uy.extu_exp == EXT_EXP_NAN &&
52		((uy.extu_frach &~ LDBL_NBIT)|uy.extu_fracl) != 0))
53		return x+y;			/* x or y is nan */
54
55	if (x == y) return y;			/* x=y, return y */
56
57	if (x == 0.0) {
58		ux.extu_frach = 0;		/* return +-minsubnormal */
59		ux.extu_fracl = 1;
60		ux.extu_sign = uy.extu_sign;
61		t = ux.extu_ld * ux.extu_ld;
62		if (t == ux.extu_ld)
63			return t;
64		else
65			return ux.extu_ld;	/* raise underflow flag */
66	}
67
68	if ((x>0.0) ^ (x<y)) {			/* x -= ulp */
69		if (ux.extu_fracl == 0) {
70			if ((ux.extu_frach & ~LDBL_NBIT) == 0)
71				ux.extu_exp -= 1;
72			ux.extu_frach = (ux.extu_frach - 1) |
73					(ux.extu_frach & LDBL_NBIT);
74		}
75		ux.extu_fracl -= 1;
76	} else {				/* x += ulp */
77		ux.extu_fracl += 1;
78		if (ux.extu_fracl == 0) {
79			ux.extu_frach = (ux.extu_frach + 1) |
80					(ux.extu_frach & LDBL_NBIT);
81			if ((ux.extu_frach & ~LDBL_NBIT) == 0)
82				ux.extu_exp += 1;
83		}
84	}
85
86	if (ux.extu_exp == EXT_EXP_INF)
87		return x+x;			/* overflow  */
88
89	if (ux.extu_exp == 0) {			/* underflow */
90#ifndef LDBL_IMPLICIT_NBIT
91		mask_nbit_l(ux);
92#endif
93		t = ux.extu_ld * ux.extu_ld;
94		if (t != ux.extu_ld)		/* raise underflow flag */
95			return ux.extu_ld;
96	}
97
98	return ux.extu_ld;
99}
100#endif
101