s_rintl.c revision 175371 
1/*-
2 * Copyright (c) 2008 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
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: head/lib/msun/src/s_rintl.c 175371 2008-01-15 23:31:24Z das $");
29
30#include <float.h>
31#include <math.h>
32
33#include "fpmath.h"
34
35#define	BIAS	(LDBL_MAX_EXP - 1)
36
37static const float
38shift[2] = {
39#if LDBL_MANT_DIG == 64
40	0x1.0p63, -0x1.0p63
41#elif LDBL_MANT_DIG == 113
42	0x1.0p112, -0x1.0p112
43#else
44#error "Unsupported long double format"
45#endif
46};
47
48long double
49rintl(long double x)
50{
51	union IEEEl2bits u;
52	short sign;
53
54	u.e = x;
55
56	if (u.bits.exp >= BIAS + LDBL_MANT_DIG - 1) {
57		/*
58		 * The biased exponent is greater than the number of digits
59		 * in the mantissa, so x is inf, NaN, or an integer.
60		 */
61		return (x);
62	}
63	sign = u.bits.sign;
64
65	/*
66	 * The following code assumes that intermediate results are
67	 * evaluated in long double precision. If they are evaluated in
68	 * greater precision, double rounding may occur, and if they are
69	 * evaluated in less precision (as on i386), results will be
70	 * wildly incorrect.
71	 */
72	x += shift[sign];
73	x -= shift[sign];
74
75	/*
76	 * If the result is +-0, then it must have the same sign as x, but
77	 * the above calculation doesn't always give this.  Fix up the sign.
78	 */
79	if (x == 0.0L)
80		return (sign ? -0.0L : 0.0L);
81	return (x);
82}
83