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
42static const float
43shift[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};
52static const float zero[2] = { 0.0, -0.0 };
53
54long double
55rintl(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