s_rintl.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2008 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
29#include <sys/cdefs.h>
30__FBSDID("$FreeBSD: stable/11/lib/msun/src/s_rintl.c 330897 2018-03-14 03:19:51Z eadler $");
31
32#include <float.h>
33#include <math.h>
34
35#include "fpmath.h"
36
37#if LDBL_MAX_EXP != 0x4000
38/* We also require the usual bias, min exp and expsign packing. */
39#error "Unsupported long double format"
40#endif
41
42#define	BIAS	(LDBL_MAX_EXP - 1)
43
44static const float
45shift[2] = {
46#if LDBL_MANT_DIG == 64
47	0x1.0p63, -0x1.0p63
48#elif LDBL_MANT_DIG == 113
49	0x1.0p112, -0x1.0p112
50#else
51#error "Unsupported long double format"
52#endif
53};
54static const float zero[2] = { 0.0, -0.0 };
55
56long double
57rintl(long double x)
58{
59	union IEEEl2bits u;
60	uint32_t expsign;
61	int ex, sign;
62
63	u.e = x;
64	expsign = u.xbits.expsign;
65	ex = expsign & 0x7fff;
66
67	if (ex >= BIAS + LDBL_MANT_DIG - 1) {
68		if (ex == BIAS + LDBL_MAX_EXP)
69			return (x + x);	/* Inf, NaN, or unsupported format */
70		return (x);		/* finite and already an integer */
71	}
72	sign = expsign >> 15;
73
74	/*
75	 * The following code assumes that intermediate results are
76	 * evaluated in long double precision. If they are evaluated in
77	 * greater precision, double rounding may occur, and if they are
78	 * evaluated in less precision (as on i386), results will be
79	 * wildly incorrect.
80	 */
81	x += shift[sign];
82	x -= shift[sign];
83
84	/*
85	 * If the result is +-0, then it must have the same sign as x, but
86	 * the above calculation doesn't always give this.  Fix up the sign.
87	 */
88	if (ex < BIAS && x == 0.0L)
89		return (zero[sign]);
90
91	return (x);
92}
93