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("$FreeBSD$");
29
30 #include <float.h>
31 #include <math.h>
32 #include <stdint.h>
33
34 #include "fpmath.h"
35
36 #if LDBL_MAX_EXP != 0x4000
37 /* We also require the usual bias, min exp and expsign packing. */
38 #error "Unsupported long double format"
39 #endif
40
41 #define BIAS (LDBL_MAX_EXP - 1)
42
43 static const float
44 shift[2] = {
45 #if LDBL_MANT_DIG == 64
46 0x1.0p63, -0x1.0p63
47 #elif LDBL_MANT_DIG == 113
48 0x1.0p112, -0x1.0p112
49 #else
50 #error "Unsupported long double format"
51 #endif
52 };
53 static const float zero[2] = { 0.0, -0.0 };
54
55 long double
rintl(long double x)56 rintl(long double x)
57 {
58 union IEEEl2bits u;
59 uint32_t expsign;
60 int ex, sign;
61
62 u.e = x;
63 expsign = u.xbits.expsign;
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