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