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 * $FreeBSD$
37 */
38
39#include <float.h>
40#include <math.h>
41#include <sys/types.h>
42
43#include "fpmath.h"
44
45#if LDBL_MANL_SIZE > 32
46#define	MASK	((uint64_t)-1)
47#else
48#define	MASK	((uint32_t)-1)
49#endif
50/* Return the last n bits of a word, representing the fractional part. */
51#define	GETFRAC(bits, n)	((bits) & ~(MASK << (n)))
52/* The number of fraction bits in manh, not counting the integer bit */
53#define	HIBITS	(LDBL_MANT_DIG - LDBL_MANL_SIZE)
54
55static const long double zero[] = { 0.0L, -0.0L };
56
57long double
58modfl(long double x, long double *iptr)
59{
60	union IEEEl2bits ux;
61	int e;
62
63	ux.e = x;
64	e = ux.bits.exp - LDBL_MAX_EXP + 1;
65	if (e < HIBITS) {			/* Integer part is in manh. */
66		if (e < 0) {			/* |x|<1 */
67			*iptr = zero[ux.bits.sign];
68			return (x);
69		} else {
70			if ((GETFRAC(ux.bits.manh, HIBITS - 1 - e) |
71			     ux.bits.manl) == 0) {	/* X is an integer. */
72				*iptr = x;
73				return (zero[ux.bits.sign]);
74			} else {
75				/* Clear all but the top e+1 bits. */
76				ux.bits.manh >>= HIBITS - 1 - e;
77				ux.bits.manh <<= HIBITS - 1 - e;
78				ux.bits.manl = 0;
79				*iptr = ux.e;
80				return (x - ux.e);
81			}
82		}
83	} else if (e >= LDBL_MANT_DIG - 1) {	/* x has no fraction part. */
84		*iptr = x;
85		if (x != x)			/* Handle NaNs. */
86			return (x);
87		return (zero[ux.bits.sign]);
88	} else {				/* Fraction part is in manl. */
89		if (GETFRAC(ux.bits.manl, LDBL_MANT_DIG - 1 - e) == 0) {
90			/* x is integral. */
91			*iptr = x;
92			return (zero[ux.bits.sign]);
93		} else {
94			/* Clear all but the top e+1 bits. */
95			ux.bits.manl >>= LDBL_MANT_DIG - 1 - e;
96			ux.bits.manl <<= LDBL_MANT_DIG - 1 - e;
97			*iptr = ux.e;
98			return (x - ux.e);
99		}
100	}
101}
102