1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * IEEE754 floating point arithmetic
4 * single precision: MADDF.f (Fused Multiply Add)
5 * MADDF.fmt: FPR[fd] = FPR[fd] + (FPR[fs] x FPR[ft])
6 *
7 * MIPS floating point support
8 * Copyright (C) 2015 Imagination Technologies, Ltd.
9 * Author: Markos Chandras <markos.chandras@imgtec.com>
10 */
11
12#include "ieee754sp.h"
13
14
15static union ieee754sp _sp_maddf(union ieee754sp z, union ieee754sp x,
16 union ieee754sp y, enum maddf_flags flags)
17{
18 int re;
19 int rs;
20 unsigned int rm;
21 u64 rm64;
22 u64 zm64;
23 int s;
24
25 COMPXSP;
26 COMPYSP;
27 COMPZSP;
28
29 EXPLODEXSP;
30 EXPLODEYSP;
31 EXPLODEZSP;
32
33 FLUSHXSP;
34 FLUSHYSP;
35 FLUSHZSP;
36
37 ieee754_clearcx();
38
39 rs = xs ^ ys;
40 if (flags & MADDF_NEGATE_PRODUCT)
41 rs ^= 1;
42 if (flags & MADDF_NEGATE_ADDITION)
43 zs ^= 1;
44
45 /*
46 * Handle the cases when at least one of x, y or z is a NaN.
47 * Order of precedence is sNaN, qNaN and z, x, y.
48 */
49 if (zc == IEEE754_CLASS_SNAN)
50 return ieee754sp_nanxcpt(z);
51 if (xc == IEEE754_CLASS_SNAN)
52 return ieee754sp_nanxcpt(x);
53 if (yc == IEEE754_CLASS_SNAN)
54 return ieee754sp_nanxcpt(y);
55 if (zc == IEEE754_CLASS_QNAN)
56 return z;
57 if (xc == IEEE754_CLASS_QNAN)
58 return x;
59 if (yc == IEEE754_CLASS_QNAN)
60 return y;
61
62 if (zc == IEEE754_CLASS_DNORM)
63 SPDNORMZ;
64 /* ZERO z cases are handled separately below */
65
66 switch (CLPAIR(xc, yc)) {
67
68
69 /*
70 * Infinity handling
71 */
72 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
73 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
74 ieee754_setcx(IEEE754_INVALID_OPERATION);
75 return ieee754sp_indef();
76
77 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
78 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
79 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
80 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
81 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
82 if ((zc == IEEE754_CLASS_INF) && (zs != rs)) {
83 /*
84 * Cases of addition of infinities with opposite signs
85 * or subtraction of infinities with same signs.
86 */
87 ieee754_setcx(IEEE754_INVALID_OPERATION);
88 return ieee754sp_indef();
89 }
90 /*
91 * z is here either not an infinity, or an infinity having the
92 * same sign as product (x*y). The result must be an infinity,
93 * and its sign is determined only by the sign of product (x*y).
94 */
95 return ieee754sp_inf(rs);
96
97 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
98 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
99 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
100 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
101 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
102 if (zc == IEEE754_CLASS_INF)
103 return ieee754sp_inf(zs);
104 if (zc == IEEE754_CLASS_ZERO) {
105 /* Handle cases +0 + (-0) and similar ones. */
106 if (zs == rs)
107 /*
108 * Cases of addition of zeros of equal signs
109 * or subtraction of zeroes of opposite signs.
110 * The sign of the resulting zero is in any
111 * such case determined only by the sign of z.
112 */
113 return z;
114
115 return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
116 }
117 /* x*y is here 0, and z is not 0, so just return z */
118 return z;
119
120 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
121 SPDNORMX;
122 fallthrough;
123 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
124 if (zc == IEEE754_CLASS_INF)
125 return ieee754sp_inf(zs);
126 SPDNORMY;
127 break;
128
129 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
130 if (zc == IEEE754_CLASS_INF)
131 return ieee754sp_inf(zs);
132 SPDNORMX;
133 break;
134
135 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
136 if (zc == IEEE754_CLASS_INF)
137 return ieee754sp_inf(zs);
138 /* continue to real computations */
139 }
140
141 /* Finally get to do some computation */
142
143 /*
144 * Do the multiplication bit first
145 *
146 * rm = xm * ym, re = xe + ye basically
147 *
148 * At this point xm and ym should have been normalized.
149 */
150
151 /* rm = xm * ym, re = xe+ye basically */
152 assert(xm & SP_HIDDEN_BIT);
153 assert(ym & SP_HIDDEN_BIT);
154
155 re = xe + ye;
156
157 /* Multiple 24 bit xm and ym to give 48 bit results */
158 rm64 = (uint64_t)xm * ym;
159
160 /* Shunt to top of word */
161 rm64 = rm64 << 16;
162
163 /* Put explicit bit at bit 62 if necessary */
164 if ((int64_t) rm64 < 0) {
165 rm64 = rm64 >> 1;
166 re++;
167 }
168
169 assert(rm64 & (1 << 62));
170
171 if (zc == IEEE754_CLASS_ZERO) {
172 /*
173 * Move explicit bit from bit 62 to bit 26 since the
174 * ieee754sp_format code expects the mantissa to be
175 * 27 bits wide (24 + 3 rounding bits).
176 */
177 rm = XSPSRS64(rm64, (62 - 26));
178 return ieee754sp_format(rs, re, rm);
179 }
180
181 /* Move explicit bit from bit 23 to bit 62 */
182 zm64 = (uint64_t)zm << (62 - 23);
183 assert(zm64 & (1 << 62));
184
185 /* Make the exponents the same */
186 if (ze > re) {
187 /*
188 * Have to shift r fraction right to align.
189 */
190 s = ze - re;
191 rm64 = XSPSRS64(rm64, s);
192 re += s;
193 } else if (re > ze) {
194 /*
195 * Have to shift z fraction right to align.
196 */
197 s = re - ze;
198 zm64 = XSPSRS64(zm64, s);
199 ze += s;
200 }
201 assert(ze == re);
202 assert(ze <= SP_EMAX);
203
204 /* Do the addition */
205 if (zs == rs) {
206 /*
207 * Generate 64 bit result by adding two 63 bit numbers
208 * leaving result in zm64, zs and ze.
209 */
210 zm64 = zm64 + rm64;
211 if ((int64_t)zm64 < 0) { /* carry out */
212 zm64 = XSPSRS1(zm64);
213 ze++;
214 }
215 } else {
216 if (zm64 >= rm64) {
217 zm64 = zm64 - rm64;
218 } else {
219 zm64 = rm64 - zm64;
220 zs = rs;
221 }
222 if (zm64 == 0)
223 return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
224
225 /*
226 * Put explicit bit at bit 62 if necessary.
227 */
228 while ((zm64 >> 62) == 0) {
229 zm64 <<= 1;
230 ze--;
231 }
232 }
233
234 /*
235 * Move explicit bit from bit 62 to bit 26 since the
236 * ieee754sp_format code expects the mantissa to be
237 * 27 bits wide (24 + 3 rounding bits).
238 */
239 zm = XSPSRS64(zm64, (62 - 26));
240
241 return ieee754sp_format(zs, ze, zm);
242}
243
244union ieee754sp ieee754sp_maddf(union ieee754sp z, union ieee754sp x,
245 union ieee754sp y)
246{
247 return _sp_maddf(z, x, y, flags: 0);
248}
249
250union ieee754sp ieee754sp_msubf(union ieee754sp z, union ieee754sp x,
251 union ieee754sp y)
252{
253 return _sp_maddf(z, x, y, flags: MADDF_NEGATE_PRODUCT);
254}
255
256union ieee754sp ieee754sp_madd(union ieee754sp z, union ieee754sp x,
257 union ieee754sp y)
258{
259 return _sp_maddf(z, x, y, flags: 0);
260}
261
262union ieee754sp ieee754sp_msub(union ieee754sp z, union ieee754sp x,
263 union ieee754sp y)
264{
265 return _sp_maddf(z, x, y, flags: MADDF_NEGATE_ADDITION);
266}
267
268union ieee754sp ieee754sp_nmadd(union ieee754sp z, union ieee754sp x,
269 union ieee754sp y)
270{
271 return _sp_maddf(z, x, y, flags: MADDF_NEGATE_PRODUCT|MADDF_NEGATE_ADDITION);
272}
273
274union ieee754sp ieee754sp_nmsub(union ieee754sp z, union ieee754sp x,
275 union ieee754sp y)
276{
277 return _sp_maddf(z, x, y, flags: MADDF_NEGATE_PRODUCT);
278}
279

source code of linux/arch/mips/math-emu/sp_maddf.c