1 // SPDX-License-Identifier: GPL-2.0-only
2 /* IEEE754 floating point arithmetic
3 * single precision
4 */
5 /*
6 * MIPS floating point support
7 * Copyright (C) 1994-2000 Algorithmics Ltd.
8 */
9
10 #include "ieee754sp.h"
11
12 union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y)
13 {
14 int s;
15
16 COMPXSP;
17 COMPYSP;
18
19 EXPLODEXSP;
20 EXPLODEYSP;
21
22 ieee754_clearcx();
23
24 FLUSHXSP;
25 FLUSHYSP;
26
27 switch (CLPAIR(xc, yc)) {
28 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
29 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
30 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
31 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
32 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
33 return ieee754sp_nanxcpt(y);
34
35 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
36 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
37 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
38 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
39 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
40 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
41 return ieee754sp_nanxcpt(x);
42
43 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
44 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
45 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
46 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
47 return y;
48
49 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
50 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
51 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
52 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
53 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
54 return x;
55
56
57 /*
58 * Infinity handling
59 */
60 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
61 if (xs != ys)
62 return x;
63 ieee754_setcx(IEEE754_INVALID_OPERATION);
64 return ieee754sp_indef();
65
66 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
67 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
68 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
69 return ieee754sp_inf(ys ^ 1);
70
71 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
72 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
73 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
74 return x;
75
76 /*
77 * Zero handling
78 */
79 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
80 if (xs != ys)
81 return x;
82 else
83 return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
84
85 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
86 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
87 return x;
88
89 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
90 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
91 /* quick fix up */
92 SPSIGN(y) ^= 1;
93 return y;
94
95 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
96 SPDNORMX;
97 fallthrough;
98 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
99 SPDNORMY;
100 break;
101
102 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
103 SPDNORMX;
104 break;
105
106 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
107 break;
108 }
109 /* flip sign of y and handle as add */
110 ys ^= 1;
111
112 assert(xm & SP_HIDDEN_BIT);
113 assert(ym & SP_HIDDEN_BIT);
114
115
116 /* provide guard,round and stick bit space */
117 xm <<= 3;
118 ym <<= 3;
119
120 if (xe > ye) {
121 /*
122 * have to shift y fraction right to align
123 */
124 s = xe - ye;
125 ym = XSPSRS(ym, s);
126 ye += s;
127 } else if (ye > xe) {
128 /*
129 * have to shift x fraction right to align
130 */
131 s = ye - xe;
132 xm = XSPSRS(xm, s);
133 xe += s;
134 }
135 assert(xe == ye);
136 assert(xe <= SP_EMAX);
137
138 if (xs == ys) {
139 /* generate 28 bit result of adding two 27 bit numbers
140 */
141 xm = xm + ym;
142
143 if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */
144 SPXSRSX1(); /* shift preserving sticky */
145 }
146 } else {
147 if (xm >= ym) {
148 xm = xm - ym;
149 } else {
150 xm = ym - xm;
151 xs = ys;
152 }
153 if (xm == 0) {
154 if (ieee754_csr.rm == FPU_CSR_RD)
155 return ieee754sp_zero(1); /* round negative inf. => sign = -1 */
156 else
157 return ieee754sp_zero(0); /* other round modes => sign = 1 */
158 }
159 /* normalize to rounding precision
160 */
161 while ((xm >> (SP_FBITS + 3)) == 0) {
162 xm <<= 1;
163 xe--;
164 }
165 }
166
167 return ieee754sp_format(xs, xe, xm);
168 }
169
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