1/*	$OpenBSD: fpu_compare.c,v 1.5 2024/03/29 21:08:10 miod Exp $	*/
2/*	$NetBSD: fpu_compare.c,v 1.3 2001/08/26 05:46:31 eeh 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/fsr.h>
54#include <machine/reg.h>
55
56#include <sparc64/fpu/fpu_arith.h>
57#include <sparc64/fpu/fpu_emu.h>
58
59/*
60 * Perform a compare instruction (with or without unordered exception).
61 * This updates the fcc field in the fsr.
62 *
63 * If either operand is NaN, the result is unordered.  For cmpe, this
64 * causes an NV exception.  Everything else is ordered:
65 *	|Inf| > |numbers| > |0|.
66 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
67 * so we get this directly.  Note, however, that two zeros compare equal
68 * regardless of sign, while everything else depends on sign.
69 *
70 * Incidentally, two Infs of the same sign compare equal (per the 80387
71 * manual---it would be nice if the SPARC documentation were more
72 * complete).
73 */
74void
75fpu_compare(struct fpemu *fe, int cmpe)
76{
77	struct fpn *a, *b;
78	int cc;
79	FPU_DECL_CARRY
80
81	a = &fe->fe_f1;
82	b = &fe->fe_f2;
83
84	if (ISNAN(a) || ISNAN(b)) {
85		/*
86		 * In any case, we already got an exception for signalling
87		 * NaNs; here we may replace that one with an identical
88		 * exception, but so what?.
89		 */
90		if (cmpe)
91			fe->fe_cx = FSR_NV;
92		cc = FSR_CC_UO;
93		goto done;
94	}
95
96	/*
97	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
98	 * at most one is 0, and if the signs differ we are done.
99	 */
100	if (ISZERO(a) && ISZERO(b)) {
101		cc = FSR_CC_EQ;
102		goto done;
103	}
104	if (a->fp_sign) {		/* a < 0 (or -0) */
105		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
106			cc = FSR_CC_LT;
107			goto done;
108		}
109	} else {			/* a > 0 (or +0) */
110		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
111			cc = FSR_CC_GT;
112			goto done;
113		}
114	}
115
116	/*
117	 * Now the signs are the same (but may both be negative).  All
118	 * we have left are these cases:
119	 *
120	 *	|a| < |b|		[classes or values differ]
121	 *	|a| > |b|		[classes or values differ]
122	 *	|a| == |b|		[classes and values identical]
123	 *
124	 * We define `diff' here to expand these as:
125	 *
126	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
127	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
128	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
129	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
130	 */
131#define opposite_cc(cc) ((cc) == FSR_CC_LT ? FSR_CC_GT : FSR_CC_LT)
132#define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
133	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
134		cc = diff(FSR_CC_LT);
135		goto done;
136	}
137	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
138		cc = diff(FSR_CC_GT);
139		goto done;
140	}
141	/* now none can be 0: only Inf and numbers remain */
142	if (ISINF(a)) {				/* |Inf| = |Inf| */
143		cc = FSR_CC_EQ;
144		goto done;
145	}
146	/*
147	 * Only numbers remain.  To compare two numbers in magnitude, we
148	 * simply subtract them.
149	 */
150	a = fpu_sub(fe);
151	if (a->fp_class == FPC_ZERO)
152		cc = FSR_CC_EQ;
153	else
154		cc = diff(FSR_CC_GT);
155
156done:
157	fe->fe_fsr = (fe->fe_fsr & ~FSR_FCC) | (cc << FSR_FCC_SHIFT);
158}
159