1 /* $NetBSD: modf.c,v 1.1 1995/02/10 17:50:25 cgd Exp $ */
4 * Copyright (c) 1994, 1995 Carnegie-Mellon University.
7 * Author: Chris G. Demetriou
9 * Permission to use, copy, modify and distribute this software and
10 * its documentation is hereby granted, provided that both the copyright
11 * notice and this permission notice appear in all copies of the
12 * software, derivative works or modified versions, and any portions
13 * thereof, and that both notices appear in supporting documentation.
15 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
16 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
17 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
19 * Carnegie Mellon requests users of this software to return to
21 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
22 * School of Computer Science
23 * Carnegie Mellon University
24 * Pittsburgh PA 15213-3890
26 * any improvements or extensions that they make and grant Carnegie the
27 * rights to redistribute these changes.
30 #include <sys/cdefs.h>
31 __FBSDID("$FreeBSD$");
33 #include <sys/types.h>
34 #include <machine/ieee.h>
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).
42 * Beware signedness when doing subtraction, and also operand size!
55 * If input is Inf or NaN, return it and leave i alone.
58 if (u.s.dbl_exp == DBL_EXP_INFNAN)
62 * If input can't have a fractional part, return
63 * (appropriately signed) zero, and make i be the input.
65 if ((int)u.s.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) {
68 v.s.dbl_sign = u.s.dbl_sign;
73 * If |input| < 1.0, return it, and set i to the appropriately
76 if (u.s.dbl_exp < DBL_EXP_BIAS) {
78 v.s.dbl_sign = u.s.dbl_sign;
84 * There can be a fractional part of the input.
85 * If you look at the math involved for a few seconds, it's
86 * plain to see that the integral part is the input, with the
87 * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed,
88 * the the fractional part is the part with the rest of the
89 * bits zeroed. Just zeroing the high bits to get the
90 * fractional part would yield a fraction in need of
91 * normalization. Therefore, we take the easy way out, and
92 * just use subtraction to get the fractional part.
95 /* Zero the low bits of the fraction, the sleazy way. */
96 frac = ((u_int64_t)v.s.dbl_frach << 32) + v.s.dbl_fracl;
97 frac >>= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
98 frac <<= DBL_FRACBITS - (u.s.dbl_exp - DBL_EXP_BIAS);
99 v.s.dbl_fracl = frac & 0xffffffff;
100 v.s.dbl_frach = frac >> 32;
104 u.s.dbl_sign = v.s.dbl_sign;