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
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/types.h>
51#include <sys/systm.h>
52
53#include <machine/fpu.h>
54
55#include <powerpc/fpu/fpu_arith.h>
56#include <powerpc/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 ordered, 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 */
73void
74fpu_compare(struct fpemu *fe, int ordered)
75{
76	struct fpn *a, *b, *r;
77	int cc;
78
79	a = &fe->fe_f1;
80	b = &fe->fe_f2;
81	r = &fe->fe_f3;
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		cc = FPSCR_FU;
90		if (ISSNAN(a) || ISSNAN(b))
91			cc |= FPSCR_VXSNAN;
92		if (ordered) {
93			if (fe->fe_fpscr & FPSCR_VE || ISQNAN(a) || ISQNAN(b))
94				cc |= FPSCR_VXVC;
95		}
96		goto done;
97	}
98
99	/*
100	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
101	 * at most one is 0, and if the signs differ we are done.
102	 */
103	if (ISZERO(a) && ISZERO(b)) {
104		cc = FPSCR_FE;
105		goto done;
106	}
107	if (a->fp_sign) {		/* a < 0 (or -0) */
108		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
109			cc = FPSCR_FL;
110			goto done;
111		}
112	} else {			/* a > 0 (or +0) */
113		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
114			cc = FPSCR_FG;
115			goto done;
116		}
117	}
118
119	/*
120	 * Now the signs are the same (but may both be negative).  All
121	 * we have left are these cases:
122	 *
123	 *	|a| < |b|		[classes or values differ]
124	 *	|a| > |b|		[classes or values differ]
125	 *	|a| == |b|		[classes and values identical]
126	 *
127	 * We define `diff' here to expand these as:
128	 *
129	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
130	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
131	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
132	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
133	 */
134#define opposite_cc(cc) ((cc) == FPSCR_FL ? FPSCR_FG : FPSCR_FL)
135#define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
136	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
137		cc = diff(FPSCR_FL);
138		goto done;
139	}
140	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
141		cc = diff(FPSCR_FG);
142		goto done;
143	}
144	/* now none can be 0: only Inf and numbers remain */
145	if (ISINF(a)) {				/* |Inf| = |Inf| */
146		cc = FPSCR_FE;
147		goto done;
148	}
149	fpu_sub(fe);
150	if (ISZERO(r))
151		cc = FPSCR_FE;
152	else if (r->fp_sign)
153		cc = FPSCR_FL;
154	else
155		cc = FPSCR_FG;
156done:
157	fe->fe_cx = cc;
158}
159