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