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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. | |
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 | ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y) | |
31 | { | |
32 | COMPXDP; | |
33 | COMPYDP; | |
34 | ||
35 | EXPLODEXDP; | |
36 | EXPLODEYDP; | |
37 | ||
38 | CLEARCX; | |
39 | ||
40 | FLUSHXDP; | |
41 | FLUSHYDP; | |
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 ieee754dp_nanxcpt(ieee754dp_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 ieee754dp_xcpt(ieee754dp_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 ieee754dp_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 ieee754dp_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 | DPDNORMX; | |
af901ca1 | 113 | /* FALL THROUGH */ |
1da177e4 LT |
114 | |
115 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): | |
116 | /* normalize ym,ye */ | |
117 | DPDNORMY; | |
118 | break; | |
119 | ||
120 | case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): | |
121 | /* normalize xm,xe */ | |
122 | DPDNORMX; | |
123 | break; | |
124 | ||
125 | case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): | |
126 | break; | |
127 | } | |
128 | /* flip sign of y and handle as add */ | |
129 | ys ^= 1; | |
130 | ||
131 | assert(xm & DP_HIDDEN_BIT); | |
132 | assert(ym & DP_HIDDEN_BIT); | |
133 | ||
134 | ||
135 | /* provide guard,round and stick bit dpace */ | |
136 | xm <<= 3; | |
137 | ym <<= 3; | |
138 | ||
139 | if (xe > ye) { | |
140 | /* have to shift y fraction right to align | |
141 | */ | |
142 | int s = xe - ye; | |
143 | ym = XDPSRS(ym, s); | |
144 | ye += s; | |
145 | } else if (ye > xe) { | |
146 | /* have to shift x fraction right to align | |
147 | */ | |
148 | int s = ye - xe; | |
149 | xm = XDPSRS(xm, s); | |
150 | xe += s; | |
151 | } | |
152 | assert(xe == ye); | |
153 | assert(xe <= DP_EMAX); | |
154 | ||
155 | if (xs == ys) { | |
156 | /* generate 28 bit result of adding two 27 bit numbers | |
157 | */ | |
158 | xm = xm + ym; | |
159 | xe = xe; | |
160 | xs = xs; | |
161 | ||
162 | if (xm >> (DP_MBITS + 1 + 3)) { /* carry out */ | |
163 | xm = XDPSRS1(xm); /* shift preserving sticky */ | |
164 | xe++; | |
165 | } | |
166 | } else { | |
167 | if (xm >= ym) { | |
168 | xm = xm - ym; | |
169 | xe = xe; | |
170 | xs = xs; | |
171 | } else { | |
172 | xm = ym - xm; | |
173 | xe = xe; | |
174 | xs = ys; | |
175 | } | |
176 | if (xm == 0) { | |
177 | if (ieee754_csr.rm == IEEE754_RD) | |
178 | return ieee754dp_zero(1); /* round negative inf. => sign = -1 */ | |
179 | else | |
180 | return ieee754dp_zero(0); /* other round modes => sign = 1 */ | |
181 | } | |
182 | ||
183 | /* normalize to rounding precision | |
184 | */ | |
185 | while ((xm >> (DP_MBITS + 3)) == 0) { | |
186 | xm <<= 1; | |
187 | xe--; | |
188 | } | |
189 | } | |
190 | DPNORMRET2(xs, xe, xm, "sub", x, y); | |
191 | } |