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fpu_compare.c revision 1.7 
      1 /*	$NetBSD: fpu_compare.c,v 1.7 2022/09/08 15:21:50 rin 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 __KERNEL_RCSID(0, "$NetBSD: fpu_compare.c,v 1.7 2022/09/08 15:21:50 rin Exp $");
     52 
     53 #include <sys/types.h>
     54 
     55 #include <machine/fpu.h>
     56 #include <machine/reg.h>
     57 
     58 #include <powerpc/fpu/fpu_arith.h>
     59 #include <powerpc/fpu/fpu_emu.h>
     60 
     61 /*
     62  * Perform a compare instruction (with or without unordered exception).
     63  * This updates the fcc field in the fsr.
     64  *
     65  * If either operand is NaN, the result is unordered.  For ordered, this
     66  * causes an NV exception.  Everything else is ordered:
     67  *	|Inf| > |numbers| > |0|.
     68  * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0),
     69  * so we get this directly.  Note, however, that two zeros compare equal
     70  * regardless of sign, while everything else depends on sign.
     71  *
     72  * Incidentally, two Infs of the same sign compare equal (per the 80387
     73  * manual---it would be nice if the SPARC documentation were more
     74  * complete).
     75  */
     76 void
     77 fpu_compare(struct fpemu *fe, int ordered)
     78 {
     79 	struct fpn *a, *b, *r;
     80 	int cc;
     81 
     82 	fe->fe_fpscr &= ~FPSCR_FPCC;
     83 
     84 	a = &fe->fe_f1;
     85 	b = &fe->fe_f2;
     86 	r = &fe->fe_f3;
     87 
     88 	if (ISNAN(a) || ISNAN(b)) {
     89 		/*
     90 		 * In any case, we already got an exception for signalling
     91 		 * NaNs; here we may replace that one with an identical
     92 		 * exception, but so what?.
     93 		 */
     94 		cc = FPSCR_FU;
     95 		if (ISSNAN(a) || ISSNAN(b))
     96 			cc |= FPSCR_VXSNAN;
     97 		if (ordered) {
     98 #ifdef notyet /* XXXRO */
     99 			if ((fe->fe_fpscr & FPSCR_VE) == 0 ||
    100 			    ISQNAN(a) || ISQNAN(b))
    101 #endif
    102 				cc |= FPSCR_VXVC;
    103 		}
    104 		goto done;
    105 	}
    106 
    107 	/*
    108 	 * Must handle both-zero early to avoid sign goofs.  Otherwise,
    109 	 * at most one is 0, and if the signs differ we are done.
    110 	 */
    111 	if (ISZERO(a) && ISZERO(b)) {
    112 		cc = FPSCR_FE;
    113 		goto done;
    114 	}
    115 	if (a->fp_sign) {		/* a < 0 (or -0) */
    116 		if (!b->fp_sign) {	/* b >= 0 (or if a = -0, b > 0) */
    117 			cc = FPSCR_FL;
    118 			goto done;
    119 		}
    120 	} else {			/* a > 0 (or +0) */
    121 		if (b->fp_sign) {	/* b <= -0 (or if a = +0, b < 0) */
    122 			cc = FPSCR_FG;
    123 			goto done;
    124 		}
    125 	}
    126 
    127 	/*
    128 	 * Now the signs are the same (but may both be negative).  All
    129 	 * we have left are these cases:
    130 	 *
    131 	 *	|a| < |b|		[classes or values differ]
    132 	 *	|a| > |b|		[classes or values differ]
    133 	 *	|a| == |b|		[classes and values identical]
    134 	 *
    135 	 * We define `diff' here to expand these as:
    136 	 *
    137 	 *	|a| < |b|, a,b >= 0: a < b => FSR_CC_LT
    138 	 *	|a| < |b|, a,b < 0:  a > b => FSR_CC_GT
    139 	 *	|a| > |b|, a,b >= 0: a > b => FSR_CC_GT
    140 	 *	|a| > |b|, a,b < 0:  a < b => FSR_CC_LT
    141 	 */
    142 #define opposite_cc(cc) ((cc) == FPSCR_FL ? FPSCR_FG : FPSCR_FL)
    143 #define	diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) :  (magnitude))
    144 	if (a->fp_class < b->fp_class) {	/* |a| < |b| */
    145 		cc = diff(FPSCR_FL);
    146 		goto done;
    147 	}
    148 	if (a->fp_class > b->fp_class) {	/* |a| > |b| */
    149 		cc = diff(FPSCR_FG);
    150 		goto done;
    151 	}
    152 	/* now none can be 0: only Inf and numbers remain */
    153 	if (ISINF(a)) {				/* |Inf| = |Inf| */
    154 		cc = FPSCR_FE;
    155 		goto done;
    156 	}
    157 	fpu_sub(fe);
    158 	if (ISZERO(r))
    159 		cc = FPSCR_FE;
    160 	else if (r->fp_sign)
    161 		cc = FPSCR_FL;
    162 	else
    163 		cc = FPSCR_FG;
    164 done:
    165 	fe->fe_cx = cc;
    166 }
    167