1 /* $NetBSD: fpu_add.c,v 1.4 2005/12/11 12:18:42 christos Exp $ */
2
3 /*-
4 * SPDX-License-Identifier: BSD-3-Clause
5 *
6 * Copyright (c) 1992, 1993
7 * The Regents of the University of California. All rights reserved.
8 *
9 * This software was developed by the Computer Systems Engineering group
10 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
11 * contributed to Berkeley.
12 *
13 * All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Lawrence Berkeley Laboratory.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 * notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 * notice, this list of conditions and the following disclaimer in the
25 * documentation and/or other materials provided with the distribution.
26 * 3. Neither the name of the University nor the names of its contributors
27 * may be used to endorse or promote products derived from this software
28 * without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
31 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
32 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
34 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
35 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
36 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
38 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
39 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
40 * SUCH DAMAGE.
41 *
42 * @(#)fpu_add.c 8.1 (Berkeley) 6/11/93
43 */
44
45 /*
46 * Perform an FPU add (return x + y).
47 *
48 * To subtract, negate y and call add.
49 */
50
51 #include <sys/cdefs.h>
52 __FBSDID("$FreeBSD$");
53
54 #include <sys/types.h>
55 #include <sys/systm.h>
56
57 #include <machine/fpu.h>
58 #include <machine/ieeefp.h>
59 #include <machine/reg.h>
60
61 #include <powerpc/fpu/fpu_arith.h>
62 #include <powerpc/fpu/fpu_emu.h>
63
64 struct fpn *
fpu_add(struct fpemu * fe)65 fpu_add(struct fpemu *fe)
66 {
67 struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r;
68 u_int r0, r1, r2, r3;
69 int rd;
70
71 /*
72 * Put the `heavier' operand on the right (see fpu_emu.h).
73 * Then we will have one of the following cases, taken in the
74 * following order:
75 *
76 * - y = NaN. Implied: if only one is a signalling NaN, y is.
77 * The result is y.
78 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN
79 * case was taken care of earlier).
80 * If x = -y, the result is NaN. Otherwise the result
81 * is y (an Inf of whichever sign).
82 * - y is 0. Implied: x = 0.
83 * If x and y differ in sign (one positive, one negative),
84 * the result is +0 except when rounding to -Inf. If same:
85 * +0 + +0 = +0; -0 + -0 = -0.
86 * - x is 0. Implied: y != 0.
87 * Result is y.
88 * - other. Implied: both x and y are numbers.
89 * Do addition a la Hennessey & Patterson.
90 */
91 DPRINTF(FPE_REG, ("fpu_add:\n"));
92 DUMPFPN(FPE_REG, x);
93 DUMPFPN(FPE_REG, y);
94 DPRINTF(FPE_REG, ("=>\n"));
95 ORDER(x, y);
96 if (ISNAN(y)) {
97 fe->fe_cx |= FPSCR_VXSNAN;
98 DUMPFPN(FPE_REG, y);
99 return (y);
100 }
101 if (ISINF(y)) {
102 if (ISINF(x) && x->fp_sign != y->fp_sign) {
103 fe->fe_cx |= FPSCR_VXISI;
104 return (fpu_newnan(fe));
105 }
106 DUMPFPN(FPE_REG, y);
107 return (y);
108 }
109 rd = ((fe->fe_fpscr) & FPSCR_RN);
110 if (ISZERO(y)) {
111 if (rd != FP_RM) /* only -0 + -0 gives -0 */
112 y->fp_sign &= x->fp_sign;
113 else /* any -0 operand gives -0 */
114 y->fp_sign |= x->fp_sign;
115 DUMPFPN(FPE_REG, y);
116 return (y);
117 }
118 if (ISZERO(x)) {
119 DUMPFPN(FPE_REG, y);
120 return (y);
121 }
122 /*
123 * We really have two numbers to add, although their signs may
124 * differ. Make the exponents match, by shifting the smaller
125 * number right (e.g., 1.011 => 0.1011) and increasing its
126 * exponent (2^3 => 2^4). Note that we do not alter the exponents
127 * of x and y here.
128 */
129 r = &fe->fe_f3;
130 r->fp_class = FPC_NUM;
131 if (x->fp_exp == y->fp_exp) {
132 r->fp_exp = x->fp_exp;
133 r->fp_sticky = 0;
134 } else {
135 if (x->fp_exp < y->fp_exp) {
136 /*
137 * Try to avoid subtract case iii (see below).
138 * This also guarantees that x->fp_sticky = 0.
139 */
140 SWAP(x, y);
141 }
142 /* now x->fp_exp > y->fp_exp */
143 r->fp_exp = x->fp_exp;
144 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp);
145 }
146 r->fp_sign = x->fp_sign;
147 if (x->fp_sign == y->fp_sign) {
148 FPU_DECL_CARRY
149
150 /*
151 * The signs match, so we simply add the numbers. The result
152 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or
153 * 11.111...0). If so, a single bit shift-right will fix it
154 * (but remember to adjust the exponent).
155 */
156 /* r->fp_mant = x->fp_mant + y->fp_mant */
157 FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]);
158 FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]);
159 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]);
160 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]);
161 if ((r->fp_mant[0] = r0) >= FP_2) {
162 (void) fpu_shr(r, 1);
163 r->fp_exp++;
164 }
165 } else {
166 FPU_DECL_CARRY
167
168 /*
169 * The signs differ, so things are rather more difficult.
170 * H&P would have us negate the negative operand and add;
171 * this is the same as subtracting the negative operand.
172 * This is quite a headache. Instead, we will subtract
173 * y from x, regardless of whether y itself is the negative
174 * operand. When this is done one of three conditions will
175 * hold, depending on the magnitudes of x and y:
176 * case i) |x| > |y|. The result is just x - y,
177 * with x's sign, but it may need to be normalized.
178 * case ii) |x| = |y|. The result is 0 (maybe -0)
179 * so must be fixed up.
180 * case iii) |x| < |y|. We goofed; the result should
181 * be (y - x), with the same sign as y.
182 * We could compare |x| and |y| here and avoid case iii,
183 * but that would take just as much work as the subtract.
184 * We can tell case iii has occurred by an overflow.
185 *
186 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0.
187 */
188 /* r->fp_mant = x->fp_mant - y->fp_mant */
189 FPU_SET_CARRY(y->fp_sticky);
190 FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]);
191 FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]);
192 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]);
193 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]);
194 if (r0 < FP_2) {
195 /* cases i and ii */
196 if ((r0 | r1 | r2 | r3) == 0) {
197 /* case ii */
198 r->fp_class = FPC_ZERO;
199 r->fp_sign = rd == FP_RM;
200 return (r);
201 }
202 } else {
203 /*
204 * Oops, case iii. This can only occur when the
205 * exponents were equal, in which case neither
206 * x nor y have sticky bits set. Flip the sign
207 * (to y's sign) and negate the result to get y - x.
208 */
209 #ifdef DIAGNOSTIC
210 if (x->fp_exp != y->fp_exp || r->fp_sticky)
211 panic("fpu_add");
212 #endif
213 r->fp_sign = y->fp_sign;
214 FPU_SUBS(r3, 0, r3);
215 FPU_SUBCS(r2, 0, r2);
216 FPU_SUBCS(r1, 0, r1);
217 FPU_SUBC(r0, 0, r0);
218 }
219 r->fp_mant[3] = r3;
220 r->fp_mant[2] = r2;
221 r->fp_mant[1] = r1;
222 r->fp_mant[0] = r0;
223 if (r0 < FP_1)
224 fpu_norm(r);
225 }
226 DUMPFPN(FPE_REG, r);
227 return (r);
228 }
229