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review.evervolv.com / android_kernel_htc_msm8960 / eb279b79c46be767ecffadaa8ed6be3e3555e93d / . / arch / mips / math-emu / sp_sub.c
blob: dbb802c1a08633d9f3df05e46f20dba53fbf173d [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -0700[diff] [blame]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
30ieee754sp 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}