1 /* $OpenBSD: fpu_compare.c,v 1.3 2003/06/02 23:27:54 millert Exp $ */
2 /* $NetBSD: fpu_compare.c,v 1.2 1994/11/20 20:52:37 deraadt Exp $ */
3
4 /*
5 * Copyright (c) 1992, 1993
6 * The Regents of the University of California. All rights reserved.
7 *
8 * This software was developed by the Computer Systems Engineering group
9 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
10 * contributed to Berkeley.
11 *
12 * All advertising materials mentioning features or use of this software
13 * must display the following acknowledgement:
14 * This product includes software developed by the University of
15 * California, Lawrence Berkeley Laboratory.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
19 * are met:
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
25 * 3. Neither the name of the University nor the names of its contributors
26 * may be used to endorse or promote products derived from this software
27 * without specific prior written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
30 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
32 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
33 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
37 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
38 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
39 * SUCH DAMAGE.
40 *
41 * @(#)fpu_compare.c 8.1 (Berkeley) 6/11/93
42 */
43
44 /*
45 * CMP and CMPE instructions.
46 *
47 * These rely on the fact that our internal wide format is achieved by
48 * adding zero bits to the end of narrower mantissas.
49 */
50
51 #include <sys/types.h>
52
53 #include <machine/reg.h>
54
55 #include <sparc/fpu/fpu_arith.h>
56 #include <sparc/fpu/fpu_emu.h>
57
58 /*
59 * Perform a compare instruction (with or without unordered exception).
60 * This updates the fcc field in the fsr.
61 *
62 * If either operand is NaN, the result is unordered. For cmpe, this
63 * causes an NV exception. Everything else is ordered:
64 * |Inf| > |numbers| > |0|.
65 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
66 * so we get this directly. Note, however, that two zeros compare equal
67 * regardless of sign, while everything else depends on sign.
68 *
69 * Incidentally, two Infs of the same sign compare equal (per the 80387
70 * manual---it would be nice if the SPARC documentation were more
71 * complete).
72 */
73 void
fpu_compare(struct fpemu * fe,int cmpe)74 fpu_compare(struct fpemu *fe, int cmpe)
75 {
76 register struct fpn *a, *b;
77 register int cc, r3, r2, r1, r0;
78 FPU_DECL_CARRY
79
80 a = &fe->fe_f1;
81 b = &fe->fe_f2;
82
83 if (ISNAN(a) || ISNAN(b)) {
84 /*
85 * In any case, we already got an exception for signalling
86 * NaNs; here we may replace that one with an identical
87 * exception, but so what?.
88 */
89 if (cmpe)
90 fe->fe_cx = FSR_NV;
91 cc = FSR_CC_UO;
92 goto done;
93 }
94
95 /*
96 * Must handle both-zero early to avoid sign goofs. Otherwise,
97 * at most one is 0, and if the signs differ we are done.
98 */
99 if (ISZERO(a) && ISZERO(b)) {
100 cc = FSR_CC_EQ;
101 goto done;
102 }
103 if (a->fp_sign) { /* a < 0 (or -0) */
104 if (!b->fp_sign) { /* b >= 0 (or if a = -0, b > 0) */
105 cc = FSR_CC_LT;
106 goto done;
107 }
108 } else { /* a > 0 (or +0) */
109 if (b->fp_sign) { /* b <= -0 (or if a = +0, b < 0) */
110 cc = FSR_CC_GT;
111 goto done;
112 }
113 }
114
115 /*
116 * Now the signs are the same (but may both be negative). All
117 * we have left are these cases:
118 *
119 * |a| < |b| [classes or values differ]
120 * |a| > |b| [classes or values differ]
121 * |a| == |b| [classes and values identical]
122 *
123 * We define `diff' here to expand these as:
124 *
125 * |a| < |b|, a,b >= 0: a < b => FSR_CC_LT
126 * |a| < |b|, a,b < 0: a > b => FSR_CC_GT
127 * |a| > |b|, a,b >= 0: a > b => FSR_CC_GT
128 * |a| > |b|, a,b < 0: a < b => FSR_CC_LT
129 */
130 #define opposite_cc(cc) ((cc) == FSR_CC_LT ? FSR_CC_GT : FSR_CC_LT)
131 #define diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) : (magnitude))
132 if (a->fp_class < b->fp_class) { /* |a| < |b| */
133 cc = diff(FSR_CC_LT);
134 goto done;
135 }
136 if (a->fp_class > b->fp_class) { /* |a| > |b| */
137 cc = diff(FSR_CC_GT);
138 goto done;
139 }
140 /* now none can be 0: only Inf and numbers remain */
141 if (ISINF(a)) { /* |Inf| = |Inf| */
142 cc = FSR_CC_EQ;
143 goto done;
144 }
145 /*
146 * Only numbers remain. To compare two numbers in magnitude, we
147 * simply subtract their mantissas.
148 */
149 FPU_SUBS(r3, a->fp_mant[0], b->fp_mant[0]);
150 FPU_SUBCS(r2, a->fp_mant[1], b->fp_mant[1]);
151 FPU_SUBCS(r1, a->fp_mant[2], b->fp_mant[2]);
152 FPU_SUBC(r0, a->fp_mant[3], b->fp_mant[3]);
153 if (r0 < 0) /* underflow: |a| < |b| */
154 cc = diff(FSR_CC_LT);
155 else if ((r0 | r1 | r2 | r3) != 0) /* |a| > |b| */
156 cc = diff(FSR_CC_GT);
157 else
158 cc = FSR_CC_EQ; /* |a| == |b| */
159 done:
160 fe->fe_fsr = (fe->fe_fsr & ~FSR_FCC) | (cc << FSR_FCC_SHIFT);
161 }
162