Annotation of src/lib/libc/gen/modf_ieee754.c, Revision 1.4
1.4 ! he 1: /* $NetBSD: modf_ieee754.c,v 1.3 2010/01/27 14:10:41 drochner Exp $ */
1.1 kleink 2:
3: /*
4: * Copyright (c) 1994, 1995 Carnegie-Mellon University.
5: * All rights reserved.
6: *
7: * Author: Chris G. Demetriou
8: *
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.
14: *
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.
18: *
19: * Carnegie Mellon requests users of this software to return to
20: *
21: * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
22: * School of Computer Science
23: * Carnegie Mellon University
24: * Pittsburgh PA 15213-3890
25: *
26: * any improvements or extensions that they make and grant Carnegie the
27: * rights to redistribute these changes.
28: */
29:
30: #include <sys/types.h>
31: #include <machine/ieee.h>
32: #include <errno.h>
33: #include <math.h>
34:
35: /*
36: * double modf(double val, double *iptr)
37: * returns: f and i such that |f| < 1.0, (f + i) = val, and
38: * sign(f) == sign(i) == sign(val).
39: *
40: * Beware signedness when doing subtraction, and also operand size!
41: */
42: double
43: modf(double val, double *iptr)
44: {
1.2 kleink 45: union ieee_double_u u, v;
1.1 kleink 46: u_int64_t frac;
47:
48: /*
1.3 drochner 49: * If input is +/-Inf or NaN, return +/-0 or NaN.
1.1 kleink 50: */
1.2 kleink 51: u.dblu_d = val;
1.3 drochner 52: if (u.dblu_dbl.dbl_exp == DBL_EXP_INFNAN) {
53: *iptr = u.dblu_d;
54: return (0.0 / u.dblu_d);
55: }
1.1 kleink 56:
57: /*
58: * If input can't have a fractional part, return
59: * (appropriately signed) zero, and make i be the input.
60: */
1.2 kleink 61: if ((int)u.dblu_dbl.dbl_exp - DBL_EXP_BIAS > DBL_FRACBITS - 1) {
62: *iptr = u.dblu_d;
63: v.dblu_d = 0.0;
64: v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign;
65: return (v.dblu_d);
1.1 kleink 66: }
67:
68: /*
69: * If |input| < 1.0, return it, and set i to the appropriately
70: * signed zero.
71: */
1.2 kleink 72: if (u.dblu_dbl.dbl_exp < DBL_EXP_BIAS) {
73: v.dblu_d = 0.0;
74: v.dblu_dbl.dbl_sign = u.dblu_dbl.dbl_sign;
75: *iptr = v.dblu_d;
76: return (u.dblu_d);
1.1 kleink 77: }
78:
79: /*
80: * There can be a fractional part of the input.
81: * If you look at the math involved for a few seconds, it's
82: * plain to see that the integral part is the input, with the
83: * low (DBL_FRACBITS - (exponent - DBL_EXP_BIAS)) bits zeroed,
84: * the fractional part is the part with the rest of the
85: * bits zeroed. Just zeroing the high bits to get the
86: * fractional part would yield a fraction in need of
87: * normalization. Therefore, we take the easy way out, and
88: * just use subtraction to get the fractional part.
89: */
1.2 kleink 90: v.dblu_d = u.dblu_d;
1.1 kleink 91: /* Zero the low bits of the fraction, the sleazy way. */
1.2 kleink 92: frac = ((u_int64_t)v.dblu_dbl.dbl_frach << 32) + v.dblu_dbl.dbl_fracl;
93: frac >>= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS);
94: frac <<= DBL_FRACBITS - (u.dblu_dbl.dbl_exp - DBL_EXP_BIAS);
1.4 ! he 95: v.dblu_dbl.dbl_fracl = (u_int) (frac & 0xffffffffULL);
! 96: v.dblu_dbl.dbl_frach = (u_int) (frac >> 32);
1.2 kleink 97: *iptr = v.dblu_d;
98:
99: u.dblu_d -= v.dblu_d;
100: u.dblu_dbl.dbl_sign = v.dblu_dbl.dbl_sign;
101: return (u.dblu_d);
1.1 kleink 102: }
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