s_nextafterl.c revision 1.1 
1/*	$NetBSD: s_nextafterl.c,v 1.1 2010/09/15 16:12:05 christos 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 1.1 2010/09/15 16:12:05 christos Exp $");
17
18#include <float.h>
19#include <math.h>
20#include <machine/ieee.h>
21
22#if LDBL_MAX_EXP != 0x4000
23#error "Unsupported long double format"
24#endif
25
26/*
27 * IEEE functions
28 *      nextafterl(x,y)
29 *      return the next machine floating-point number of x in the
30 *      direction toward y.
31 *   Special cases:
32 *	If x == y, y shall be returned
33 *	If x or y is NaN, a NaN shall be returned
34 */
35long double
36nextafterl(long double x, long double y)
37{
38	volatile long double t;
39	union ieee_ext_u ux, uy;
40
41	ux.extu_ld = x;
42	uy.extu_ld = y;
43
44	if ((ux.extu_exp == EXT_EXP_NAN &&
45		((ux.extu_frach &~ LDBL_NBIT)|ux.extu_fracl) != 0) ||
46	    (uy.extu_exp == EXT_EXP_NAN &&
47		((uy.extu_frach &~ LDBL_NBIT)|uy.extu_fracl) != 0))
48		return x+y;			/* x or y is nan */
49
50	if (x == y) return y;			/* x=y, return y */
51
52	if (x == 0.0) {
53		ux.extu_frach = 0;		/* return +-minsubnormal */
54		ux.extu_fracl = 1;
55		ux.extu_sign = uy.extu_sign;
56		t = ux.extu_ld * ux.extu_ld;
57		if (t == ux.extu_ld)
58			return t;
59		else
60			return ux.extu_ld;	/* raise underflow flag */
61	}
62
63	if ((x>0.0) ^ (x<y)) {			/* x -= ulp */
64		if (ux.extu_fracl == 0) {
65			if ((ux.extu_frach & ~LDBL_NBIT) == 0)
66				ux.extu_exp -= 1;
67			ux.extu_frach = (ux.extu_frach - 1) |
68					(ux.extu_frach & LDBL_NBIT);
69		}
70		ux.extu_fracl -= 1;
71	} else {				/* x += ulp */
72		ux.extu_fracl += 1;
73		if (ux.extu_fracl == 0) {
74			ux.extu_frach = (ux.extu_frach + 1) |
75					(ux.extu_frach & LDBL_NBIT);
76			if ((ux.extu_frach & ~LDBL_NBIT) == 0)
77				ux.extu_exp += 1;
78		}
79	}
80
81	if (ux.extu_exp == EXT_EXP_INF)
82		return x+x;			/* overflow  */
83
84	if (ux.extu_exp == 0) {			/* underflow */
85		mask_nbit_l(ux);
86		t = ux.extu_ld * ux.extu_ld;
87		if (t != ux.extu_ld)		/* raise underflow flag */
88			return ux.extu_ld;
89	}
90
91	return ux.extu_ld;
92}
93