1/*	$NetBSD: fpu_compare.c,v 1.3.22.3 2004/09/21 13:22:14 skrll 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. Neither the name of the University nor the names of its contributors
25 *    may be used to endorse or promote products derived from this software
26 *    without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38 * SUCH DAMAGE.
39 *
40 *	@(#)fpu_compare.c	8.1 (Berkeley) 6/11/93
41 */
42
43/*
44 * CMP and CMPE instructions.
45 *
46 * These rely on the fact that our internal wide format is achieved by
47 * adding zero bits to the end of narrower mantissas.
48 */
49
50#include <sys/cdefs.h>
51__KERNEL_RCSID(0, "$NetBSD: fpu_compare.c,v 1.3.22.3 2004/09/21 13:22:14 skrll Exp $");
52
53#include <sys/types.h>
54
55#include <machine/reg.h>
56
57#include <sparc/fpu/fpu_arith.h>
58#include <sparc/fpu/fpu_emu.h>
59
60/*
61 * Perform a compare instruction (with or without unordered exception).
62 * This updates the fcc field in the fsr.
63 *
64 * If either operand is NaN, the result is unordered.  For cmpe, this
65 * causes an NV exception.  Everything else is ordered:
66 *	|Inf| > |numbers| > |0|.
67 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
68 * so we get this directly.  Note, however, that two zeros compare equal
69 * regardless of sign, while everything else depends on sign.
70 *
71 * Incidentally, two Infs of the same sign compare equal (per the 80387
72 * manual---it would be nice if the SPARC documentation were more
73 * complete).
74 */
75void
76fpu_compare(struct fpemu *fe, int cmpe)
77{
78	register struct fpn *a, *b;
79	register int cc;
80	FPU_DECL_CARRY
81
82	a = &fe->fe_f1;
83	b = &fe->fe_f2;
84
85	if (ISNAN(a) || ISNAN(b)) {
86		/*
87		 * In any case, we already got an exception for signalling
88		 * NaNs; here we may replace that one with an identical
89		 * exception, but so what?.
90		 */
91		if (cmpe)
92			fe->fe_cx = FSR_NV;
93		cc = FSR_CC_UO;
94		goto done;
95	}
96
97	/*
98	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
99	 * at most one is 0, and if the signs differ we are done.
100	 */
101	if (ISZERO(a) && ISZERO(b)) {
102		cc = FSR_CC_EQ;
103		goto done;
104	}
105	if (a->fp_sign) {		/* a < 0 (or -0) */
106		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
107			cc = FSR_CC_LT;
108			goto done;
109		}
110	} else {			/* a > 0 (or +0) */
111		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
112			cc = FSR_CC_GT;
113			goto done;
114		}
115	}
116
117	/*
118	 * Now the signs are the same (but may both be negative).  All
119	 * we have left are these cases:
120	 *
121	 *	|a| < |b|		[classes or values differ]
122	 *	|a| > |b|		[classes or values differ]
123	 *	|a| == |b|		[classes and values identical]
124	 *
125	 * We define `diff' here to expand these as:
126	 *
127	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
128	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
129	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
130	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
131	 */
132#define opposite_cc(cc) ((cc) == FSR_CC_LT ? FSR_CC_GT : FSR_CC_LT)
133#define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
134	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
135		cc = diff(FSR_CC_LT);
136		goto done;
137	}
138	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
139		cc = diff(FSR_CC_GT);
140		goto done;
141	}
142	/* now none can be 0: only Inf and numbers remain */
143	if (ISINF(a)) {				/* |Inf| = |Inf| */
144		cc = FSR_CC_EQ;
145		goto done;
146	}
147	/*
148	 * Only numbers remain.  To compare two numbers in magnitude, we
149	 * simply subtract them.
150	 */
151	a = fpu_sub(fe);
152	if (a->fp_class == FPC_ZERO)
153		cc = FSR_CC_EQ;
154	else
155		cc = diff(FSR_CC_GT);
156
157done:
158	fe->fe_fsr = (fe->fe_fsr & ~FSR_FCC) | (cc << FSR_FCC_SHIFT);
159}
160