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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 LT |
7 | * |
8 | * ######################################################################## | |
9 | * | |
10 | * This program is free software; you can distribute it and/or modify it | |
11 | * under the terms of the GNU General Public License (Version 2) as | |
12 | * published by the Free Software Foundation. | |
13 | * | |
14 | * This program is distributed in the hope it will be useful, but WITHOUT | |
15 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
16 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
17 | * for more details. | |
18 | * | |
19 | * You should have received a copy of the GNU General Public License along | |
20 | * with this program; if not, write to the Free Software Foundation, Inc., | |
21 | * 59 Temple Place - Suite 330, Boston MA 02111-1307, USA. | |
22 | * | |
23 | * ######################################################################## | |
24 | */ | |
25 | ||
26 | ||
27 | #include "ieee754dp.h" | |
28 | ||
29 | ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y) | |
30 | { | |
31 | COMPXDP; | |
32 | COMPYDP; | |
33 | ||
34 | EXPLODEXDP; | |
35 | EXPLODEYDP; | |
36 | ||
37 | CLEARCX; | |
38 | ||
39 | FLUSHXDP; | |
40 | FLUSHYDP; | |
41 | ||
42 | switch (CLPAIR(xc, yc)) { | |
43 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): | |
44 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): | |
45 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): | |
46 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): | |
47 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): | |
48 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): | |
49 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): | |
50 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): | |
51 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): | |
52 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): | |
53 | case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): | |
54 | SETCX(IEEE754_INVALID_OPERATION); | |
55 | return ieee754dp_nanxcpt(ieee754dp_indef(), "sub", x, y); | |
56 | ||
57 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): | |
58 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): | |
59 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): | |
60 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): | |
61 | return y; | |
62 | ||
63 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): | |
64 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): | |
65 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): | |
66 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): | |
67 | case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): | |
68 | return x; | |
69 | ||
70 | ||
71 | /* Infinity handling | |
72 | */ | |
73 | ||
74 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): | |
75 | if (xs != ys) | |
76 | return x; | |
77 | SETCX(IEEE754_INVALID_OPERATION); | |
78 | return ieee754dp_xcpt(ieee754dp_indef(), "sub", x, y); | |
79 | ||
80 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): | |
81 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): | |
82 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): | |
83 | return ieee754dp_inf(ys ^ 1); | |
84 | ||
85 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): | |
86 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): | |
87 | case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): | |
88 | return x; | |
89 | ||
90 | /* Zero handling | |
91 | */ | |
92 | ||
93 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): | |
94 | if (xs != ys) | |
95 | return x; | |
96 | else | |
97 | return ieee754dp_zero(ieee754_csr.rm == | |
98 | IEEE754_RD); | |
99 | ||
100 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): | |
101 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): | |
102 | return x; | |
103 | ||
104 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): | |
105 | case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): | |
106 | /* quick fix up */ | |
107 | DPSIGN(y) ^= 1; | |
108 | return y; | |
109 | ||
110 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): | |
111 | DPDNORMX; | |
af901ca1 | 112 | /* FALL THROUGH */ |
1da177e4 LT |
113 | |
114 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): | |
115 | /* normalize ym,ye */ | |
116 | DPDNORMY; | |
117 | break; | |
118 | ||
119 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): | |
120 | /* normalize xm,xe */ | |
121 | DPDNORMX; | |
122 | break; | |
123 | ||
124 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): | |
125 | break; | |
126 | } | |
127 | /* flip sign of y and handle as add */ | |
128 | ys ^= 1; | |
129 | ||
130 | assert(xm & DP_HIDDEN_BIT); | |
131 | assert(ym & DP_HIDDEN_BIT); | |
132 | ||
133 | ||
134 | /* provide guard,round and stick bit dpace */ | |
135 | xm <<= 3; | |
136 | ym <<= 3; | |
137 | ||
138 | if (xe > ye) { | |
139 | /* have to shift y fraction right to align | |
140 | */ | |
141 | int s = xe - ye; | |
142 | ym = XDPSRS(ym, s); | |
143 | ye += s; | |
144 | } else if (ye > xe) { | |
145 | /* have to shift x fraction right to align | |
146 | */ | |
147 | int s = ye - xe; | |
148 | xm = XDPSRS(xm, s); | |
149 | xe += s; | |
150 | } | |
151 | assert(xe == ye); | |
152 | assert(xe <= DP_EMAX); | |
153 | ||
154 | if (xs == ys) { | |
155 | /* generate 28 bit result of adding two 27 bit numbers | |
156 | */ | |
157 | xm = xm + ym; | |
158 | xe = xe; | |
159 | xs = xs; | |
160 | ||
161 | if (xm >> (DP_MBITS + 1 + 3)) { /* carry out */ | |
162 | xm = XDPSRS1(xm); /* shift preserving sticky */ | |
163 | xe++; | |
164 | } | |
165 | } else { | |
166 | if (xm >= ym) { | |
167 | xm = xm - ym; | |
168 | xe = xe; | |
169 | xs = xs; | |
170 | } else { | |
171 | xm = ym - xm; | |
172 | xe = xe; | |
173 | xs = ys; | |
174 | } | |
175 | if (xm == 0) { | |
176 | if (ieee754_csr.rm == IEEE754_RD) | |
177 | return ieee754dp_zero(1); /* round negative inf. => sign = -1 */ | |
178 | else | |
179 | return ieee754dp_zero(0); /* other round modes => sign = 1 */ | |
180 | } | |
181 | ||
182 | /* normalize to rounding precision | |
183 | */ | |
184 | while ((xm >> (DP_MBITS + 3)) == 0) { | |
185 | xm <<= 1; | |
186 | xe--; | |
187 | } | |
188 | } | |
189 | DPNORMRET2(xs, xe, xm, "sub", x, y); | |
190 | } |