1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
|
// SPDX-License-Identifier: GPL-2.0-only
/* IEEE754 floating point arithmetic
* double precision: common utilities
*/
/*
* MIPS floating point support
* Copyright (C) 1994-2000 Algorithmics Ltd.
*/
#include "ieee754dp.h"
union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y)
{
int s;
COMPXDP;
COMPYDP;
EXPLODEXDP;
EXPLODEYDP;
ieee754_clearcx();
FLUSHXDP;
FLUSHYDP;
switch (CLPAIR(xc, yc)) {
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
return ieee754dp_nanxcpt(y);
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
return ieee754dp_nanxcpt(x);
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
return y;
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
return x;
/*
* Infinity handling
*/
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
if (xs != ys)
return x;
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754dp_indef();
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
return ieee754dp_inf(ys ^ 1);
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
return x;
/*
* Zero handling
*/
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
if (xs != ys)
return x;
else
return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
return x;
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
/* quick fix up */
DPSIGN(y) ^= 1;
return y;
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
DPDNORMX;
fallthrough;
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
/* normalize ym,ye */
DPDNORMY;
break;
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
/* normalize xm,xe */
DPDNORMX;
break;
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
break;
}
/* flip sign of y and handle as add */
ys ^= 1;
assert(xm & DP_HIDDEN_BIT);
assert(ym & DP_HIDDEN_BIT);
/* provide guard,round and stick bit dpace */
xm <<= 3;
ym <<= 3;
if (xe > ye) {
/*
* Have to shift y fraction right to align
*/
s = xe - ye;
ym = XDPSRS(ym, s);
ye += s;
} else if (ye > xe) {
/*
* Have to shift x fraction right to align
*/
s = ye - xe;
xm = XDPSRS(xm, s);
xe += s;
}
assert(xe == ye);
assert(xe <= DP_EMAX);
if (xs == ys) {
/* generate 28 bit result of adding two 27 bit numbers
*/
xm = xm + ym;
if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
xm = XDPSRS1(xm); /* shift preserving sticky */
xe++;
}
} else {
if (xm >= ym) {
xm = xm - ym;
} else {
xm = ym - xm;
xs = ys;
}
if (xm == 0) {
if (ieee754_csr.rm == FPU_CSR_RD)
return ieee754dp_zero(1); /* round negative inf. => sign = -1 */
else
return ieee754dp_zero(0); /* other round modes => sign = 1 */
}
/* normalize to rounding precision
*/
while ((xm >> (DP_FBITS + 3)) == 0) {
xm <<= 1;
xe--;
}
}
return ieee754dp_format(xs, xe, xm);
}
|
