1 /* $OpenBSD: modf.c,v 1.7 2023/08/13 06:55:37 miod 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 +/-0 or NaN.
55 */
56 u.v = val;
57 if (u.s.dbl_exp == DBL_EXP_INFNAN) {
58 *iptr = u.v;
59 return (0.0 / u.v);
60 }
61
62 /*
63 * If input can't have a fractional part, return
64 * (appropriately signed) zero, and make i be the input.
65 */
66 if ((int)u.s.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) {
67 *iptr = u.v;
68 v.v = 0.0;
69 v.s.dbl_sign = u.s.dbl_sign;
70 return (v.v);
71 }
72
73 /*
74 * If |input| < 1.0, return it, and set i to the appropriately
75 * signed zero.
76 */
77 if (u.s.dbl_exp < DBL_EXP_BIAS) {
78 v.v = 0.0;
79 v.s.dbl_sign = u.s.dbl_sign;
80 *iptr = v.v;
81 return (u.v);
82 }
83
84 /*
85 * There can be a fractional part of the input.
86 * If you look at the math involved for a few seconds, it's
87 * plain to see that the integral part is the input, with the
88 * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed,
89 * the fractional part is the part with the rest of the
90 * bits zeroed. Just zeroing the high bits to get the
91 * fractional part would yield a fraction in need of
92 * normalization. Therefore, we take the easy way out, and
93 * just use subtraction to get the fractional part.
94 */
95 v.v = u.v;
96 /* Zero the low bits of the fraction, the sleazy way. */
97 frac = ((u_int64_t)v.s.dbl_frach << 32) + v.s.dbl_fracl;
98 frac >>= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
99 frac <<= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
100 v.s.dbl_fracl = frac & 0xffffffff;
101 v.s.dbl_frach = frac >> 32;
102 *iptr = v.v;
103
104 u.v -= v.v;
105 u.s.dbl_sign = v.s.dbl_sign;
106 return (u.v);
107 }
108
109 #if LDBL_MANT_DIG == DBL_MANT_DIG
110 __strong_alias(modfl, modf);
111 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */
112