1 /* $OpenBSD: s_rintl.c,v 1.2 2016/09/12 19:47:02 guenther Exp $ */
2 /*-
3 * Copyright (c) 2008 David Schultz <das@FreeBSD.ORG>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #include <sys/types.h>
29 #include <machine/ieee.h>
30 #include <float.h>
31 #include <math.h>
32
33 #if LDBL_MAX_EXP != 0x4000
34 /* We also require the usual bias, min exp and expsign packing. */
35 #error "Unsupported long double format"
36 #endif
37
38 #define BIAS (LDBL_MAX_EXP - 1)
39
40 static const float
41 shift[2] = {
42 #if LDBL_MANT_DIG == 64
43 0x1.0p63, -0x1.0p63
44 #elif LDBL_MANT_DIG == 113
45 0x1.0p112, -0x1.0p112
46 #else
47 #error "Unsupported long double format"
48 #endif
49 };
50 static const float zero[2] = { 0.0, -0.0 };
51
52 long double
rintl(long double x)53 rintl(long double x)
54 {
55 union {
56 long double e;
57 struct ieee_ext bits;
58 } u;
59 uint32_t expsign;
60 int ex, sign;
61
62 u.e = x;
63 expsign = (u.bits.ext_sign << 15) | u.bits.ext_exp;
64 ex = expsign & 0x7fff;
65
66 if (ex >= BIAS + LDBL_MANT_DIG - 1) {
67 if (ex == BIAS + LDBL_MAX_EXP)
68 return (x + x); /* Inf, NaN, or unsupported format */
69 return (x); /* finite and already an integer */
70 }
71 sign = expsign >> 15;
72
73 /*
74 * The following code assumes that intermediate results are
75 * evaluated in long double precision. If they are evaluated in
76 * greater precision, double rounding may occur, and if they are
77 * evaluated in less precision (as on i386), results will be
78 * wildly incorrect.
79 */
80 x += shift[sign];
81 x -= shift[sign];
82
83 /*
84 * If the result is +-0, then it must have the same sign as x, but
85 * the above calculation doesn't always give this. Fix up the sign.
86 */
87 if (ex < BIAS && x == 0.0L)
88 return (zero[sign]);
89
90 return (x);
91 }
92 DEF_NONSTD(rintl);
93