1 /* $OpenBSD: fpu_compare.c,v 1.4 2024/03/29 21:02:11 miod Exp $ */
2
3 /*
4 * Copyright (c) 1992, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This software was developed by the Computer Systems Engineering group
8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
9 * contributed to Berkeley.
10 *
11 * All advertising materials mentioning features or use of this software
12 * must display the following acknowledgement:
13 * This product includes software developed by the University of
14 * California, Lawrence Berkeley Laboratory.
15 *
16 * Redistribution and use in source and binary forms, with or without
17 * modification, are permitted provided that the following conditions
18 * are met:
19 * 1. Redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer.
21 * 2. Redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution.
24 * 3. All advertising materials mentioning features or use of this software
25 * must display the following acknowledgement:
26 * This product includes software developed by the University of
27 * California, Berkeley and its contributors.
28 * 4. Neither the name of the University nor the names of its contributors
29 * may be used to endorse or promote products derived from this software
30 * without specific prior written permission.
31 *
32 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
33 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
34 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
35 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
36 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
37 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
38 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
40 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
41 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
42 * SUCH DAMAGE.
43 *
44 * @(#)fpu_compare.c 8.1 (Berkeley) 6/11/93
45 * $NetBSD: fpu_compare.c,v 1.3 2001/08/26 05:46:31 eeh Exp $
46 */
47
48 /*
49 * CMP and CMPE instructions.
50 *
51 * These rely on the fact that our internal wide format is achieved by
52 * adding zero bits to the end of narrower mantissas.
53 */
54
55 #include <sys/types.h>
56
57 #include <machine/fsr.h>
58
59 #include "fpu_arith.h"
60 #include "fpu_emu.h"
61 #include "fpu_extern.h"
62
63 static u_long fcc_nmask[] = {
64 ~FSR_FCC,
65 ~FSR_FCC1,
66 ~FSR_FCC2,
67 ~FSR_FCC3
68 };
69
70 /* XXX: we don't use the FSR_FCCx macros here; it's much easier this way. */
71 static int fcc_shift[] = {
72 FSR_FCC_SHIFT,
73 FSR_FCC1_SHIFT,
74 FSR_FCC2_SHIFT,
75 FSR_FCC3_SHIFT
76 };
77
78 /*
79 * Perform a compare instruction (with or without unordered exception).
80 * This updates the fcc field in the fsr.
81 *
82 * If either operand is NaN, the result is unordered. For cmpe, this
83 * causes an NV exception. Everything else is ordered:
84 * |Inf| > |numbers| > |0|.
85 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
86 * so we get this directly. Note, however, that two zeros compare equal
87 * regardless of sign, while everything else depends on sign.
88 *
89 * Incidentally, two Infs of the same sign compare equal (per the 80387
90 * manual---it would be nice if the SPARC documentation were more
91 * complete).
92 */
93 void
__fpu_compare(struct fpemu * fe,int cmpe,int fcc)94 __fpu_compare(struct fpemu *fe, int cmpe, int fcc)
95 {
96 struct fpn *a, *b;
97 int cc;
98 FPU_DECL_CARRY
99
100 a = &fe->fe_f1;
101 b = &fe->fe_f2;
102
103 if (ISNAN(a) || ISNAN(b)) {
104 /*
105 * In any case, we already got an exception for signalling
106 * NaNs; here we may replace that one with an identical
107 * exception, but so what?.
108 */
109 if (cmpe)
110 fe->fe_cx = FSR_NV;
111 cc = FSR_CC_UO;
112 goto done;
113 }
114
115 /*
116 * Must handle both-zero early to avoid sign goofs. Otherwise,
117 * at most one is 0, and if the signs differ we are done.
118 */
119 if (ISZERO(a) && ISZERO(b)) {
120 cc = FSR_CC_EQ;
121 goto done;
122 }
123 if (a->fp_sign) { /* a < 0 (or -0) */
124 if (!b->fp_sign) { /* b >= 0 (or if a = -0, b > 0) */
125 cc = FSR_CC_LT;
126 goto done;
127 }
128 } else { /* a > 0 (or +0) */
129 if (b->fp_sign) { /* b <= -0 (or if a = +0, b < 0) */
130 cc = FSR_CC_GT;
131 goto done;
132 }
133 }
134
135 /*
136 * Now the signs are the same (but may both be negative). All
137 * we have left are these cases:
138 *
139 * |a| < |b| [classes or values differ]
140 * |a| > |b| [classes or values differ]
141 * |a| == |b| [classes and values identical]
142 *
143 * We define `diff' here to expand these as:
144 *
145 * |a| < |b|, a,b >= 0: a < b => FSR_CC_LT
146 * |a| < |b|, a,b < 0: a > b => FSR_CC_GT
147 * |a| > |b|, a,b >= 0: a > b => FSR_CC_GT
148 * |a| > |b|, a,b < 0: a < b => FSR_CC_LT
149 */
150 #define opposite_cc(cc) ((cc) == FSR_CC_LT ? FSR_CC_GT : FSR_CC_LT)
151 #define diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) : (magnitude))
152 if (a->fp_class < b->fp_class) { /* |a| < |b| */
153 cc = diff(FSR_CC_LT);
154 goto done;
155 }
156 if (a->fp_class > b->fp_class) { /* |a| > |b| */
157 cc = diff(FSR_CC_GT);
158 goto done;
159 }
160 /* now none can be 0: only Inf and numbers remain */
161 if (ISINF(a)) { /* |Inf| = |Inf| */
162 cc = FSR_CC_EQ;
163 goto done;
164 }
165 /*
166 * Only numbers remain. To compare two numbers in magnitude, we
167 * simply subtract them.
168 */
169 a = __fpu_sub(fe);
170 if (a->fp_class == FPC_ZERO)
171 cc = FSR_CC_EQ;
172 else
173 cc = diff(FSR_CC_GT);
174
175 done:
176 fe->fe_fsr = (fe->fe_fsr & fcc_nmask[fcc]) |
177 ((u_long)cc << fcc_shift[fcc]);
178 }
179