1 /* $NetBSD: s_rintl.c,v 1.7 2024/05/04 19:21:51 riastradh Exp $ */
2
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 #if 0
31 __FBSDID("$FreeBSD: src/lib/msun/src/s_rintl.c,v 1.5 2008/02/22 11:59:05 bde Exp $");
32 #else
33 __RCSID("$NetBSD: s_rintl.c,v 1.7 2024/05/04 19:21:51 riastradh Exp $");
34 #endif
35
36 #include <float.h>
37 #include <machine/ieee.h>
38
39 #include "math.h"
40 #include "math_private.h"
41
42 #define BIAS (LDBL_MAX_EXP - 1)
43
44 static const float
45 shift[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 };
54 static const float zero[2] = { 0.0, -0.0 };
55
56 long double
rintl(long double x)57 rintl(long double x)
58 {
59 union ieee_ext_u u;
60 uint32_t expsign;
61 int ex, sign;
62
63 u.extu_ld = x;
64 expsign = GET_EXPSIGN(&u);
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