s_modfl.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 *
28 * Derived from s_modf.c, which has the following Copyright:
29 * ====================================================
30 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
31 *
32 * Developed at SunPro, a Sun Microsystems, Inc. business.
33 * Permission to use, copy, modify, and distribute this
34 * software is freely granted, provided that this notice
35 * is preserved.
36 * ====================================================
37 *
38 * $FreeBSD: stable/11/lib/msun/src/s_modfl.c 330897 2018-03-14 03:19:51Z eadler $
39 */
40
41#include <float.h>
42#include <math.h>
43#include <sys/types.h>
44
45#include "fpmath.h"
46
47#if LDBL_MANL_SIZE > 32
48#define	MASK	((uint64_t)-1)
49#else
50#define	MASK	((uint32_t)-1)
51#endif
52/* Return the last n bits of a word, representing the fractional part. */
53#define	GETFRAC(bits, n)	((bits) & ~(MASK << (n)))
54/* The number of fraction bits in manh, not counting the integer bit */
55#define	HIBITS	(LDBL_MANT_DIG - LDBL_MANL_SIZE)
56
57static const long double zero[] = { 0.0L, -0.0L };
58
59long double
60modfl(long double x, long double *iptr)
61{
62	union IEEEl2bits ux;
63	int e;
64
65	ux.e = x;
66	e = ux.bits.exp - LDBL_MAX_EXP + 1;
67	if (e < HIBITS) {			/* Integer part is in manh. */
68		if (e < 0) {			/* |x|<1 */
69			*iptr = zero[ux.bits.sign];
70			return (x);
71		} else {
72			if ((GETFRAC(ux.bits.manh, HIBITS - 1 - e) |
73			     ux.bits.manl) == 0) {	/* X is an integer. */
74				*iptr = x;
75				return (zero[ux.bits.sign]);
76			} else {
77				/* Clear all but the top e+1 bits. */
78				ux.bits.manh >>= HIBITS - 1 - e;
79				ux.bits.manh <<= HIBITS - 1 - e;
80				ux.bits.manl = 0;
81				*iptr = ux.e;
82				return (x - ux.e);
83			}
84		}
85	} else if (e >= LDBL_MANT_DIG - 1) {	/* x has no fraction part. */
86		*iptr = x;
87		if (x != x)			/* Handle NaNs. */
88			return (x);
89		return (zero[ux.bits.sign]);
90	} else {				/* Fraction part is in manl. */
91		if (GETFRAC(ux.bits.manl, LDBL_MANT_DIG - 1 - e) == 0) {
92			/* x is integral. */
93			*iptr = x;
94			return (zero[ux.bits.sign]);
95		} else {
96			/* Clear all but the top e+1 bits. */
97			ux.bits.manl >>= LDBL_MANT_DIG - 1 - e;
98			ux.bits.manl <<= LDBL_MANT_DIG - 1 - e;
99			*iptr = ux.e;
100			return (x - ux.e);
101		}
102	}
103}
104