xref: /minix3/lib/libm/src/lrintf.c (revision 0a6a1f1d05b60e214de2f05a7310ddd1f0e590e7)
1 /* $NetBSD: lrintf.c,v 1.6 2015/07/09 06:17:13 nat Exp $ */
2 
3 /*-
4  * Copyright (c) 2004
5  *	Matthias Drochner. 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 <math.h>
30 #include <sys/ieee754.h>
31 #include <machine/limits.h>
32 #include "math_private.h"
33 
34 #ifndef LRINTNAME
35 #define LRINTNAME lrintf
36 #define RESTYPE long int
37 #define RESTYPE_MIN LONG_MIN
38 #define RESTYPE_MAX LONG_MAX
39 #endif
40 
41 #define RESTYPE_BITS (sizeof(RESTYPE) * 8)
42 
43 static const float
44 TWO23[2]={
45   8.3886080000e+06, /* 0x4b000000 */
46  -8.3886080000e+06, /* 0xcb000000 */
47 };
48 
49 RESTYPE
LRINTNAME(float x)50 LRINTNAME(float x)
51 {
52 	u_int32_t i0;
53 	int e, s, shift;
54 	RESTYPE res;
55 #ifdef __i386__ /* XXX gcc4 will omit the rounding otherwise */
56 	volatile
57 #endif
58 		float w;
59 
60 	GET_FLOAT_WORD(i0, x);
61 	e = i0 >> SNG_FRACBITS;
62 	s = (uint32_t)e >> SNG_EXPBITS;
63 	e = (e & 0xff) - SNG_EXP_BIAS;
64 
65 	/* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
66 	if (e < -1)
67 		return (0);
68 	/* 1.0 x 2^31 (or 2^63) is already too large */
69 	if (e >= (int)RESTYPE_BITS - 1)
70 		return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */
71 
72 	/* >= 2^23 is already an exact integer */
73 	if (e < SNG_FRACBITS) {
74 		/* round, using current direction */
75 		w = TWO23[s] + x;
76 		x = w - TWO23[s];
77 	} else
78 		return x;
79 
80 	GET_FLOAT_WORD(i0, x);
81 	e = ((i0 >> SNG_FRACBITS) & 0xff) - SNG_EXP_BIAS;
82 	i0 &= 0x7fffff;
83 	i0 |= (1 << SNG_FRACBITS);
84 
85 	shift = e - SNG_FRACBITS;
86 	if (shift >=0)
87 		res = (shift < 32 ? (RESTYPE)i0 << shift : 0);
88 	else
89 		res = (shift > -32 ? i0 >> -shift : 0);
90 
91 	return (s ? -res : res);
92 }
93