File: /usr/src/linux/arch/mips/math-emu/dp_modf.c

1     /* IEEE754 floating point arithmetic
2      * double precision: common utilities
3      */
4     /*
5      * MIPS floating point support
6      * Copyright (C) 1994-2000 Algorithmics Ltd.  All rights reserved.
7      * http://www.algor.co.uk
8      *
9      * ########################################################################
10      *
11      *  This program is free software; you can distribute it and/or modify it
12      *  under the terms of the GNU General Public License (Version 2) as
13      *  published by the Free Software Foundation.
14      *
15      *  This program is distributed in the hope it will be useful, but WITHOUT
16      *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17      *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
18      *  for more details.
19      *
20      *  You should have received a copy of the GNU General Public License along
21      *  with this program; if not, write to the Free Software Foundation, Inc.,
22      *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
23      *
24      * ########################################################################
25      */
26     
27     
28     #include "ieee754dp.h"
29     
30     /* modf function is always exact for a finite number
31     */
32     ieee754dp ieee754dp_modf(ieee754dp x, ieee754dp * ip)
33     {
34     	COMPXDP;
35     
36     	CLEARCX;
37     
38     	EXPLODEXDP;
39     
40     	switch (xc) {
41     	case IEEE754_CLASS_SNAN:
42     	case IEEE754_CLASS_QNAN:
43     	case IEEE754_CLASS_INF:
44     	case IEEE754_CLASS_ZERO:
45     		*ip = x;
46     		return x;
47     	case IEEE754_CLASS_DNORM:
48     		/* far to small */
49     		*ip = ieee754dp_zero(xs);
50     		return x;
51     	case IEEE754_CLASS_NORM:
52     		break;
53     	}
54     	if (xe < 0) {
55     		*ip = ieee754dp_zero(xs);
56     		return x;
57     	}
58     	if (xe >= DP_MBITS) {
59     		*ip = x;
60     		return ieee754dp_zero(xs);
61     	}
62     	/* generate ipart mantissa by clearing bottom bits 
63     	 */
64     	*ip = builddp(xs, xe + DP_EBIAS,
65     		      ((xm >> (DP_MBITS - xe)) << (DP_MBITS - xe)) &
66     		      ~DP_HIDDEN_BIT);
67     
68     	/* generate fpart mantissa by clearing top bits
69     	 * and normalizing (must be able to normalize)
70     	 */
71     	xm = (xm << (64 - (DP_MBITS - xe))) >> (64 - (DP_MBITS - xe));
72     	if (xm == 0)
73     		return ieee754dp_zero(xs);
74     
75     	while ((xm >> DP_MBITS) == 0) {
76     		xm <<= 1;
77     		xe--;
78     	}
79     	return builddp(xs, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
80     }
81