fpu_compare.c revision 330897 
1/*	$NetBSD: fpu_compare.c,v 1.4 2005/12/11 12:18:42 christos Exp $ */
2
3/*-
4 * SPDX-License-Identifier: BSD-3-Clause
5 *
6 * Copyright (c) 1992, 1993
7 *	The Regents of the University of California.  All rights reserved.
8 *
9 * This software was developed by the Computer Systems Engineering group
10 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
11 * contributed to Berkeley.
12 *
13 * All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Lawrence Berkeley Laboratory.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 *    notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 *    notice, this list of conditions and the following disclaimer in the
25 *    documentation and/or other materials provided with the distribution.
26 * 3. Neither the name of the University nor the names of its contributors
27 *    may be used to endorse or promote products derived from this software
28 *    without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
31 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
32 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
34 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
35 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
36 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
38 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
39 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
40 * SUCH DAMAGE.
41 *
42 *	@(#)fpu_compare.c	8.1 (Berkeley) 6/11/93
43 */
44
45/*
46 * FCMPU and FCMPO instructions.
47 *
48 * These rely on the fact that our internal wide format is achieved by
49 * adding zero bits to the end of narrower mantissas.
50 */
51
52#include <sys/cdefs.h>
53__FBSDID("$FreeBSD: stable/11/sys/powerpc/fpu/fpu_compare.c 330897 2018-03-14 03:19:51Z eadler $");
54
55#include <sys/types.h>
56#include <sys/systm.h>
57
58#include <machine/fpu.h>
59#include <machine/reg.h>
60
61#include <powerpc/fpu/fpu_arith.h>
62#include <powerpc/fpu/fpu_emu.h>
63
64/*
65 * Perform a compare instruction (with or without unordered exception).
66 * This updates the fcc field in the fsr.
67 *
68 * If either operand is NaN, the result is unordered.  For ordered, this
69 * causes an NV exception.  Everything else is ordered:
70 *	|Inf| > |numbers| > |0|.
71 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
72 * so we get this directly.  Note, however, that two zeros compare equal
73 * regardless of sign, while everything else depends on sign.
74 *
75 * Incidentally, two Infs of the same sign compare equal (per the 80387
76 * manual---it would be nice if the SPARC documentation were more
77 * complete).
78 */
79void
80fpu_compare(struct fpemu *fe, int ordered)
81{
82	struct fpn *a, *b, *r;
83	int cc;
84
85	a = &fe->fe_f1;
86	b = &fe->fe_f2;
87	r = &fe->fe_f3;
88
89	if (ISNAN(a) || ISNAN(b)) {
90		/*
91		 * In any case, we already got an exception for signalling
92		 * NaNs; here we may replace that one with an identical
93		 * exception, but so what?.
94		 */
95		cc = FPSCR_FU;
96		if (ISSNAN(a) || ISSNAN(b))
97			cc |= FPSCR_VXSNAN;
98		if (ordered) {
99			if (fe->fe_fpscr & FPSCR_VE || ISQNAN(a) || ISQNAN(b))
100				cc |= FPSCR_VXVC;
101		}
102		goto done;
103	}
104
105	/*
106	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
107	 * at most one is 0, and if the signs differ we are done.
108	 */
109	if (ISZERO(a) && ISZERO(b)) {
110		cc = FPSCR_FE;
111		goto done;
112	}
113	if (a->fp_sign) {		/* a < 0 (or -0) */
114		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
115			cc = FPSCR_FL;
116			goto done;
117		}
118	} else {			/* a > 0 (or +0) */
119		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
120			cc = FPSCR_FG;
121			goto done;
122		}
123	}
124
125	/*
126	 * Now the signs are the same (but may both be negative).  All
127	 * we have left are these cases:
128	 *
129	 *	|a| < |b|		[classes or values differ]
130	 *	|a| > |b|		[classes or values differ]
131	 *	|a| == |b|		[classes and values identical]
132	 *
133	 * We define `diff' here to expand these as:
134	 *
135	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
136	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
137	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
138	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
139	 */
140#define opposite_cc(cc) ((cc) == FPSCR_FL ? FPSCR_FG : FPSCR_FL)
141#define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
142	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
143		cc = diff(FPSCR_FL);
144		goto done;
145	}
146	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
147		cc = diff(FPSCR_FG);
148		goto done;
149	}
150	/* now none can be 0: only Inf and numbers remain */
151	if (ISINF(a)) {				/* |Inf| = |Inf| */
152		cc = FPSCR_FE;
153		goto done;
154	}
155	fpu_sub(fe);
156	if (ISZERO(r))
157		cc = FPSCR_FE;
158	else if (r->fp_sign)
159		cc = FPSCR_FL;
160	else
161		cc = FPSCR_FG;
162done:
163	fe->fe_cx = cc;
164}
165