1/*-
2 * Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * Derived from s_modf.c, which has the following Copyright:
27 * ====================================================
28 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
29 *
30 * Developed at SunPro, a Sun Microsystems, Inc. business.
31 * Permission to use, copy, modify, and distribute this
32 * software is freely granted, provided that this notice
33 * is preserved.
34 * ====================================================
35 *
36 * $FreeBSD: head/lib/msun/src/s_modfl.c 165855 2007-01-07 07:54:21Z das $
37 */
38#include <sys/cdefs.h>
39__RCSID("$NetBSD: s_modfl.c,v 1.2 2024/05/15 00:02:56 riastradh Exp $");
40
41#include "namespace.h"
42
43#include <float.h>
44#include <math.h>
45#include <stdint.h>
46#include <machine/ieee.h>
47
48#ifdef __HAVE_LONG_DOUBLE
49
50#ifdef __weak_alias
51__weak_alias(modfl, _modfl)
52#endif
53
54#if EXT_FRACLBITS > 32
55#define	MASK	((uint64_t)-1)
56#else
57#define	MASK	((uint32_t)-1)
58#endif
59/* Return the last n bits of a word, representing the fractional part. */
60#define	GETFRAC(bits, n)	((bits) & ~(MASK << (n)))
61/* The number of fraction bits in manh, not counting the integer bit */
62#define	HIBITS	(LDBL_MANT_DIG - EXT_FRACLBITS)
63
64static const long double zero[] = { 0.0L, -0.0L };
65
66long double
67modfl(long double x, long double *iptr)
68{
69	union ieee_ext_u ux = { .extu_ld = x, };
70	int e = ux.extu_exp - LDBL_MAX_EXP + 1;
71
72	if (e < HIBITS) {			/* Integer part is in manh. */
73		if (e < 0) {			/* |x|<1 */
74			*iptr = zero[ux.extu_sign];
75			return (x);
76		} else {
77			if ((GETFRAC(ux.extu_frach, HIBITS - 1 - e) |
78			     ux.extu_fracl) == 0) {	/* X is an integer. */
79				*iptr = x;
80				return (zero[ux.extu_sign]);
81			} else {
82				/* Clear all but the top e+1 bits. */
83				ux.extu_frach >>= HIBITS - 1 - e;
84				ux.extu_frach <<= HIBITS - 1 - e;
85				ux.extu_fracl = 0;
86				*iptr = ux.extu_ld;
87				return (x - ux.extu_ld);
88			}
89		}
90	} else if (e >= LDBL_MANT_DIG - 1) {	/* x has no fraction part. */
91		*iptr = x;
92		if (x != x)			/* Handle NaNs. */
93			return (x);
94		return (zero[ux.extu_sign]);
95	} else {				/* Fraction part is in manl. */
96		if (GETFRAC(ux.extu_fracl, LDBL_MANT_DIG - 1 - e) == 0) {
97			/* x is integral. */
98			*iptr = x;
99			return (zero[ux.extu_sign]);
100		} else {
101			/* Clear all but the top e+1 bits. */
102			ux.extu_fracl >>= LDBL_MANT_DIG - 1 - e;
103			ux.extu_fracl <<= LDBL_MANT_DIG - 1 - e;
104			*iptr = ux.extu_ld;
105			return (x - ux.extu_ld);
106		}
107	}
108}
109#endif /* __HAVE_LONG_DOUBLE */
110