Commit | Line | Data |
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1da177e4 LT |
1 | /* IEEE754 floating point arithmetic |
2 | * double precision: common utilities | |
3 | */ | |
4 | /* | |
5 | * MIPS floating point support | |
6 | * Copyright (C) 1994-2000 Algorithmics Ltd. | |
1da177e4 | 7 | * |
1da177e4 LT |
8 | * This program is free software; you can distribute it and/or modify it |
9 | * under the terms of the GNU General Public License (Version 2) as | |
10 | * published by the Free Software Foundation. | |
11 | * | |
12 | * This program is distributed in the hope it will be useful, but WITHOUT | |
13 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
14 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
15 | * for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU General Public License along | |
18 | * with this program; if not, write to the Free Software Foundation, Inc., | |
3f7cac41 | 19 | * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
1da177e4 LT |
20 | */ |
21 | ||
1da177e4 LT |
22 | #include "ieee754dp.h" |
23 | ||
2209bcb1 | 24 | union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y) |
1da177e4 | 25 | { |
3f7cac41 RB |
26 | int s; |
27 | ||
1da177e4 LT |
28 | COMPXDP; |
29 | COMPYDP; | |
30 | ||
31 | EXPLODEXDP; | |
32 | EXPLODEYDP; | |
33 | ||
9e8bad1f | 34 | ieee754_clearcx(); |
1da177e4 LT |
35 | |
36 | FLUSHXDP; | |
37 | FLUSHYDP; | |
38 | ||
39 | switch (CLPAIR(xc, yc)) { | |
1da177e4 | 40 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): |
1da177e4 LT |
41 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): |
42 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): | |
43 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): | |
44 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): | |
d5afa7e9 MR |
45 | return ieee754dp_nanxcpt(y); |
46 | ||
47 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): | |
48 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): | |
1da177e4 LT |
49 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): |
50 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): | |
51 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): | |
52 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): | |
d5afa7e9 | 53 | return ieee754dp_nanxcpt(x); |
1da177e4 LT |
54 | |
55 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): | |
56 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): | |
57 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): | |
58 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): | |
59 | return y; | |
60 | ||
61 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): | |
62 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): | |
63 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): | |
64 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): | |
65 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): | |
66 | return x; | |
67 | ||
68 | ||
3f7cac41 RB |
69 | /* |
70 | * Infinity handling | |
71 | */ | |
1da177e4 LT |
72 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): |
73 | if (xs != ys) | |
74 | return x; | |
9e8bad1f | 75 | ieee754_setcx(IEEE754_INVALID_OPERATION); |
90efba36 | 76 | return ieee754dp_indef(); |
1da177e4 LT |
77 | |
78 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): | |
79 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): | |
80 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): | |
81 | return ieee754dp_inf(ys ^ 1); | |
82 | ||
83 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): | |
84 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): | |
85 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): | |
86 | return x; | |
87 | ||
3f7cac41 RB |
88 | /* |
89 | * Zero handling | |
90 | */ | |
1da177e4 LT |
91 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): |
92 | if (xs != ys) | |
93 | return x; | |
94 | else | |
56a64733 | 95 | return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD); |
1da177e4 LT |
96 | |
97 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): | |
98 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): | |
99 | return x; | |
100 | ||
101 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): | |
102 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): | |
103 | /* quick fix up */ | |
104 | DPSIGN(y) ^= 1; | |
105 | return y; | |
106 | ||
107 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): | |
108 | DPDNORMX; | |
af901ca1 | 109 | /* FALL THROUGH */ |
1da177e4 LT |
110 | |
111 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): | |
112 | /* normalize ym,ye */ | |
113 | DPDNORMY; | |
114 | break; | |
115 | ||
116 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): | |
117 | /* normalize xm,xe */ | |
118 | DPDNORMX; | |
119 | break; | |
120 | ||
121 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): | |
122 | break; | |
123 | } | |
124 | /* flip sign of y and handle as add */ | |
125 | ys ^= 1; | |
126 | ||
127 | assert(xm & DP_HIDDEN_BIT); | |
128 | assert(ym & DP_HIDDEN_BIT); | |
129 | ||
130 | ||
131 | /* provide guard,round and stick bit dpace */ | |
132 | xm <<= 3; | |
133 | ym <<= 3; | |
134 | ||
135 | if (xe > ye) { | |
3f7cac41 RB |
136 | /* |
137 | * Have to shift y fraction right to align | |
1da177e4 | 138 | */ |
3f7cac41 | 139 | s = xe - ye; |
1da177e4 LT |
140 | ym = XDPSRS(ym, s); |
141 | ye += s; | |
142 | } else if (ye > xe) { | |
3f7cac41 RB |
143 | /* |
144 | * Have to shift x fraction right to align | |
1da177e4 | 145 | */ |
3f7cac41 | 146 | s = ye - xe; |
1da177e4 LT |
147 | xm = XDPSRS(xm, s); |
148 | xe += s; | |
149 | } | |
150 | assert(xe == ye); | |
151 | assert(xe <= DP_EMAX); | |
152 | ||
153 | if (xs == ys) { | |
154 | /* generate 28 bit result of adding two 27 bit numbers | |
155 | */ | |
156 | xm = xm + ym; | |
1da177e4 | 157 | |
ad8fb553 | 158 | if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */ |
1da177e4 LT |
159 | xm = XDPSRS1(xm); /* shift preserving sticky */ |
160 | xe++; | |
161 | } | |
162 | } else { | |
163 | if (xm >= ym) { | |
164 | xm = xm - ym; | |
1da177e4 LT |
165 | } else { |
166 | xm = ym - xm; | |
1da177e4 LT |
167 | xs = ys; |
168 | } | |
169 | if (xm == 0) { | |
56a64733 | 170 | if (ieee754_csr.rm == FPU_CSR_RD) |
1da177e4 LT |
171 | return ieee754dp_zero(1); /* round negative inf. => sign = -1 */ |
172 | else | |
173 | return ieee754dp_zero(0); /* other round modes => sign = 1 */ | |
174 | } | |
175 | ||
176 | /* normalize to rounding precision | |
177 | */ | |
ad8fb553 | 178 | while ((xm >> (DP_FBITS + 3)) == 0) { |
1da177e4 LT |
179 | xm <<= 1; |
180 | xe--; | |
181 | } | |
182 | } | |
90efba36 RB |
183 | |
184 | return ieee754dp_format(xs, xe, xm); | |
1da177e4 | 185 | } |