Linux-2.6.12-rc2
[pandora-kernel.git] / arch / mips / math-emu / sp_sub.c
1 /* IEEE754 floating point arithmetic
2  * single precision
3  */
4 /*
5  * MIPS floating point support
6  * Copyright (C) 1994-2000 Algorithmics Ltd.
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 "ieee754sp.h"
29
30 ieee754sp ieee754sp_sub(ieee754sp x, ieee754sp y)
31 {
32         COMPXSP;
33         COMPYSP;
34
35         EXPLODEXSP;
36         EXPLODEYSP;
37
38         CLEARCX;
39
40         FLUSHXSP;
41         FLUSHYSP;
42
43         switch (CLPAIR(xc, yc)) {
44         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
45         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
46         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
47         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
48         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
49         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
50         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
51         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
52         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
53         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
54         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
55                 SETCX(IEEE754_INVALID_OPERATION);
56                 return ieee754sp_nanxcpt(ieee754sp_indef(), "sub", x, y);
57
58         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
59         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
60         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
61         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
62                 return y;
63
64         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
65         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
66         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
67         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
68         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
69                 return x;
70
71
72                 /* Infinity handling
73                  */
74
75         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
76                 if (xs != ys)
77                         return x;
78                 SETCX(IEEE754_INVALID_OPERATION);
79                 return ieee754sp_xcpt(ieee754sp_indef(), "sub", x, y);
80
81         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
82         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
83         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
84                 return ieee754sp_inf(ys ^ 1);
85
86         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
87         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
88         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
89                 return x;
90
91                 /* Zero handling
92                  */
93
94         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
95                 if (xs != ys)
96                         return x;
97                 else
98                         return ieee754sp_zero(ieee754_csr.rm ==
99                                               IEEE754_RD);
100
101         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
102         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
103                 return x;
104
105         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
106         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
107                 /* quick fix up */
108                 DPSIGN(y) ^= 1;
109                 return y;
110
111         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
112                 SPDNORMX;
113
114         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
115                 SPDNORMY;
116                 break;
117
118         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
119                 SPDNORMX;
120                 break;
121
122         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
123                 break;
124         }
125         /* flip sign of y and handle as add */
126         ys ^= 1;
127
128         assert(xm & SP_HIDDEN_BIT);
129         assert(ym & SP_HIDDEN_BIT);
130
131
132         /* provide guard,round and stick bit space */
133         xm <<= 3;
134         ym <<= 3;
135
136         if (xe > ye) {
137                 /* have to shift y fraction right to align
138                  */
139                 int s = xe - ye;
140                 SPXSRSYn(s);
141         } else if (ye > xe) {
142                 /* have to shift x fraction right to align
143                  */
144                 int s = ye - xe;
145                 SPXSRSXn(s);
146         }
147         assert(xe == ye);
148         assert(xe <= SP_EMAX);
149
150         if (xs == ys) {
151                 /* generate 28 bit result of adding two 27 bit numbers
152                  */
153                 xm = xm + ym;
154                 xe = xe;
155                 xs = xs;
156
157                 if (xm >> (SP_MBITS + 1 + 3)) { /* carry out */
158                         SPXSRSX1();     /* shift preserving sticky */
159                 }
160         } else {
161                 if (xm >= ym) {
162                         xm = xm - ym;
163                         xe = xe;
164                         xs = xs;
165                 } else {
166                         xm = ym - xm;
167                         xe = xe;
168                         xs = ys;
169                 }
170                 if (xm == 0) {
171                         if (ieee754_csr.rm == IEEE754_RD)
172                                 return ieee754sp_zero(1);       /* round negative inf. => sign = -1 */
173                         else
174                                 return ieee754sp_zero(0);       /* other round modes   => sign = 1 */
175                 }
176                 /* normalize to rounding precision
177                  */
178                 while ((xm >> (SP_MBITS + 3)) == 0) {
179                         xm <<= 1;
180                         xe--;
181                 }
182         }
183         SPNORMRET2(xs, xe, xm, "sub", x, y);
184 }