1 /* $OpenBSD: modf.c,v 1.6 2013/07/03 04:46:36 espie Exp $ */
2 /* $NetBSD: modf.c,v 1.1 1995/02/10 17:50:25 cgd Exp $ */
3
4 /*
5 * Copyright (c) 1994, 1995 Carnegie-Mellon University.
6 * All rights reserved.
7 *
8 * Author: Chris G. Demetriou
9 *
10 * Permission to use, copy, modify and distribute this software and
11 * its documentation is hereby granted, provided that both the copyright
12 * notice and this permission notice appear in all copies of the
13 * software, derivative works or modified versions, and any portions
14 * thereof, and that both notices appear in supporting documentation.
15 *
16 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
17 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
18 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
19 *
20 * Carnegie Mellon requests users of this software to return to
21 *
22 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
23 * School of Computer Science
24 * Carnegie Mellon University
25 * Pittsburgh PA 15213-3890
26 *
27 * any improvements or extensions that they make and grant Carnegie the
28 * rights to redistribute these changes.
29 */
30
31 #include <sys/types.h>
32 #include <machine/ieee.h>
33 #include <errno.h>
34 #include <float.h>
35 #include <math.h>
36
37 /*
38 * double modf(double val, double *iptr)
39 * returns: f and i such that |f| < 1.0, (f + i) = val, and
40 * sign(f) == sign(i) == sign(val).
41 *
42 * Beware signedness when doing subtraction, and also operand size!
43 */
44 double
modf(double val,double * iptr)45 modf(double val, double *iptr)
46 {
47 union doub {
48 double v;
49 struct ieee_double s;
50 } u, v;
51 u_int64_t frac;
52
53 /*
54 * If input is Inf or NaN, return it and leave i alone.
55 */
56 u.v = val;
57 if (u.s.dbl_exp == DBL_EXP_INFNAN)
58 return (u.v);
59
60 /*
61 * If input can't have a fractional part, return
62 * (appropriately signed) zero, and make i be the input.
63 */
64 if ((int)u.s.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) {
65 *iptr = u.v;
66 v.v = 0.0;
67 v.s.dbl_sign = u.s.dbl_sign;
68 return (v.v);
69 }
70
71 /*
72 * If |input| < 1.0, return it, and set i to the appropriately
73 * signed zero.
74 */
75 if (u.s.dbl_exp < DBL_EXP_BIAS) {
76 v.v = 0.0;
77 v.s.dbl_sign = u.s.dbl_sign;
78 *iptr = v.v;
79 return (u.v);
80 }
81
82 /*
83 * There can be a fractional part of the input.
84 * If you look at the math involved for a few seconds, it's
85 * plain to see that the integral part is the input, with the
86 * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed,
87 * the fractional part is the part with the rest of the
88 * bits zeroed. Just zeroing the high bits to get the
89 * fractional part would yield a fraction in need of
90 * normalization. Therefore, we take the easy way out, and
91 * just use subtraction to get the fractional part.
92 */
93 v.v = u.v;
94 /* Zero the low bits of the fraction, the sleazy way. */
95 frac = ((u_int64_t)v.s.dbl_frach << 32) + v.s.dbl_fracl;
96 frac >>= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
97 frac <<= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
98 v.s.dbl_fracl = frac & 0xffffffff;
99 v.s.dbl_frach = frac >> 32;
100 *iptr = v.v;
101
102 u.v -= v.v;
103 u.s.dbl_sign = v.s.dbl_sign;
104 return (u.v);
105 }
106
107 #if LDBL_MANT_DIG == DBL_MANT_DIG
108 __strong_alias(modfl, modf);
109 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */
110