s_rintl.c revision 176458 
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 176458 2008-02-22 10:04:53Z bde $");
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};
47static const float zero[2] = { 0.0, -0.0 };
48
49long double
50rintl(long double x)
51{
52	union IEEEl2bits u;
53	short sign;
54
55	u.e = x;
56
57	if (u.bits.exp >= BIAS + LDBL_MANT_DIG - 1) {
58		if (u.bits.exp == BIAS + LDBL_MAX_EXP)
59			return (x + x);	/* Inf, NaN, or unsupported format */
60		return (x);		/* finite and already an integer */
61	}
62	sign = u.bits.sign;
63
64	/*
65	 * The following code assumes that intermediate results are
66	 * evaluated in long double precision. If they are evaluated in
67	 * greater precision, double rounding may occur, and if they are
68	 * evaluated in less precision (as on i386), results will be
69	 * wildly incorrect.
70	 */
71	x += shift[sign];
72	x -= shift[sign];
73
74	/*
75	 * If the result is +-0, then it must have the same sign as x, but
76	 * the above calculation doesn't always give this.  Fix up the sign.
77	 */
78	if (u.bits.exp < BIAS && x == 0.0L)
79		return (zero[sign]);
80
81	return (x);
82}
83