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fpu_compare.c revision 1.1 
      1 /*	$NetBSD: fpu_compare.c,v 1.1 2001/06/13 06:01:47 simonb 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. All advertising materials mentioning features or use of this software
     25  *    must display the following acknowledgement:
     26  *	This product includes software developed by the University of
     27  *	California, Berkeley and its contributors.
     28  * 4. Neither the name of the University nor the names of its contributors
     29  *    may be used to endorse or promote products derived from this software
     30  *    without specific prior written permission.
     31  *
     32  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     33  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     34  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     35  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     36  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     37  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     38  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     39  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     40  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     41  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     42  * SUCH DAMAGE.
     43  *
     44  *	@(#)fpu_compare.c	8.1 (Berkeley) 6/11/93
     45  */
     46 
     47 /*
     48  * FCMPU and FCMPO instructions.
     49  *
     50  * These rely on the fact that our internal wide format is achieved by
     51  * adding zero bits to the end of narrower mantissas.
     52  */
     53 
     54 #include <sys/types.h>
     55 
     56 #include <machine/reg.h>
     57 #include <machine/fpu.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  */
     77 void
     78 fpu_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;
    160 done:
    161 	fe->fe_cx = cc;
    162 }
    163