1/*	$NetBSD: fpu_compare.c,v 1.4 2005/12/11 12:18:42 christos 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 * FCMPU and FCMPO 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__FBSDID("$FreeBSD$");
52
53#include <sys/types.h>
54#include <sys/systm.h>
55
56#include <machine/fpu.h>
57#include <machine/reg.h>
58
59#include <powerpc/fpu/fpu_arith.h>
60#include <powerpc/fpu/fpu_emu.h>
61
62/*
63 * Perform a compare instruction (with or without unordered exception).
64 * This updates the fcc field in the fsr.
65 *
66 * If either operand is NaN, the result is unordered.  For ordered, this
67 * causes an NV exception.  Everything else is ordered:
68 *	|Inf| > |numbers| > |0|.
69 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
70 * so we get this directly.  Note, however, that two zeros compare equal
71 * regardless of sign, while everything else depends on sign.
72 *
73 * Incidentally, two Infs of the same sign compare equal (per the 80387
74 * manual---it would be nice if the SPARC documentation were more
75 * complete).
76 */
77void
78fpu_compare(struct fpemu *fe, int ordered)
79{
80	struct fpn *a, *b, *r;
81	int cc;
82
83	a = &fe->fe_f1;
84	b = &fe->fe_f2;
85	r = &fe->fe_f3;
86
87	if (ISNAN(a) || ISNAN(b)) {
88		/*
89		 * In any case, we already got an exception for signalling
90		 * NaNs; here we may replace that one with an identical
91		 * exception, but so what?.
92		 */
93		cc = FPSCR_FU;
94		if (ISSNAN(a) || ISSNAN(b))
95			cc |= FPSCR_VXSNAN;
96		if (ordered) {
97			if (fe->fe_fpscr & FPSCR_VE || ISQNAN(a) || ISQNAN(b))
98				cc |= FPSCR_VXVC;
99		}
100		goto done;
101	}
102
103	/*
104	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
105	 * at most one is 0, and if the signs differ we are done.
106	 */
107	if (ISZERO(a) && ISZERO(b)) {
108		cc = FPSCR_FE;
109		goto done;
110	}
111	if (a->fp_sign) {		/* a < 0 (or -0) */
112		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
113			cc = FPSCR_FL;
114			goto done;
115		}
116	} else {			/* a > 0 (or +0) */
117		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
118			cc = FPSCR_FG;
119			goto done;
120		}
121	}
122
123	/*
124	 * Now the signs are the same (but may both be negative).  All
125	 * we have left are these cases:
126	 *
127	 *	|a| < |b|		[classes or values differ]
128	 *	|a| > |b|		[classes or values differ]
129	 *	|a| == |b|		[classes and values identical]
130	 *
131	 * We define `diff' here to expand these as:
132	 *
133	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
134	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
135	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
136	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
137	 */
138#define opposite_cc(cc) ((cc) == FPSCR_FL ? FPSCR_FG : FPSCR_FL)
139#define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
140	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
141		cc = diff(FPSCR_FL);
142		goto done;
143	}
144	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
145		cc = diff(FPSCR_FG);
146		goto done;
147	}
148	/* now none can be 0: only Inf and numbers remain */
149	if (ISINF(a)) {				/* |Inf| = |Inf| */
150		cc = FPSCR_FE;
151		goto done;
152	}
153	fpu_sub(fe);
154	if (ISZERO(r))
155		cc = FPSCR_FE;
156	else if (r->fp_sign)
157		cc = FPSCR_FL;
158	else
159		cc = FPSCR_FG;
160done:
161	fe->fe_cx = cc;
162}
163