1 /* $OpenBSD: fpu_compare.c,v 1.4 2024/03/29 21:02:11 miod 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 * $NetBSD: fpu_compare.c,v 1.3 2001/08/26 05:46:31 eeh Exp $ 46 */ 47 48 /* 49 * CMP and CMPE instructions. 50 * 51 * These rely on the fact that our internal wide format is achieved by 52 * adding zero bits to the end of narrower mantissas. 53 */ 54 55 #include <sys/types.h> 56 57 #include <machine/fsr.h> 58 59 #include "fpu_arith.h" 60 #include "fpu_emu.h" 61 #include "fpu_extern.h" 62 63 static u_long fcc_nmask[] = { 64 ~FSR_FCC, 65 ~FSR_FCC1, 66 ~FSR_FCC2, 67 ~FSR_FCC3 68 }; 69 70 /* XXX: we don't use the FSR_FCCx macros here; it's much easier this way. */ 71 static int fcc_shift[] = { 72 FSR_FCC_SHIFT, 73 FSR_FCC1_SHIFT, 74 FSR_FCC2_SHIFT, 75 FSR_FCC3_SHIFT 76 }; 77 78 /* 79 * Perform a compare instruction (with or without unordered exception). 80 * This updates the fcc field in the fsr. 81 * 82 * If either operand is NaN, the result is unordered. For cmpe, this 83 * causes an NV exception. Everything else is ordered: 84 * |Inf| > |numbers| > |0|. 85 * We already arranged for fp_class(Inf) > fp_class(numbers) > fp_class(0), 86 * so we get this directly. Note, however, that two zeros compare equal 87 * regardless of sign, while everything else depends on sign. 88 * 89 * Incidentally, two Infs of the same sign compare equal (per the 80387 90 * manual---it would be nice if the SPARC documentation were more 91 * complete). 92 */ 93 void 94 __fpu_compare(struct fpemu *fe, int cmpe, int fcc) 95 { 96 struct fpn *a, *b; 97 int cc; 98 FPU_DECL_CARRY 99 100 a = &fe->fe_f1; 101 b = &fe->fe_f2; 102 103 if (ISNAN(a) || ISNAN(b)) { 104 /* 105 * In any case, we already got an exception for signalling 106 * NaNs; here we may replace that one with an identical 107 * exception, but so what?. 108 */ 109 if (cmpe) 110 fe->fe_cx = FSR_NV; 111 cc = FSR_CC_UO; 112 goto done; 113 } 114 115 /* 116 * Must handle both-zero early to avoid sign goofs. Otherwise, 117 * at most one is 0, and if the signs differ we are done. 118 */ 119 if (ISZERO(a) && ISZERO(b)) { 120 cc = FSR_CC_EQ; 121 goto done; 122 } 123 if (a->fp_sign) { /* a < 0 (or -0) */ 124 if (!b->fp_sign) { /* b >= 0 (or if a = -0, b > 0) */ 125 cc = FSR_CC_LT; 126 goto done; 127 } 128 } else { /* a > 0 (or +0) */ 129 if (b->fp_sign) { /* b <= -0 (or if a = +0, b < 0) */ 130 cc = FSR_CC_GT; 131 goto done; 132 } 133 } 134 135 /* 136 * Now the signs are the same (but may both be negative). All 137 * we have left are these cases: 138 * 139 * |a| < |b| [classes or values differ] 140 * |a| > |b| [classes or values differ] 141 * |a| == |b| [classes and values identical] 142 * 143 * We define `diff' here to expand these as: 144 * 145 * |a| < |b|, a,b >= 0: a < b => FSR_CC_LT 146 * |a| < |b|, a,b < 0: a > b => FSR_CC_GT 147 * |a| > |b|, a,b >= 0: a > b => FSR_CC_GT 148 * |a| > |b|, a,b < 0: a < b => FSR_CC_LT 149 */ 150 #define opposite_cc(cc) ((cc) == FSR_CC_LT ? FSR_CC_GT : FSR_CC_LT) 151 #define diff(magnitude) (a->fp_sign ? opposite_cc(magnitude) : (magnitude)) 152 if (a->fp_class < b->fp_class) { /* |a| < |b| */ 153 cc = diff(FSR_CC_LT); 154 goto done; 155 } 156 if (a->fp_class > b->fp_class) { /* |a| > |b| */ 157 cc = diff(FSR_CC_GT); 158 goto done; 159 } 160 /* now none can be 0: only Inf and numbers remain */ 161 if (ISINF(a)) { /* |Inf| = |Inf| */ 162 cc = FSR_CC_EQ; 163 goto done; 164 } 165 /* 166 * Only numbers remain. To compare two numbers in magnitude, we 167 * simply subtract them. 168 */ 169 a = __fpu_sub(fe); 170 if (a->fp_class == FPC_ZERO) 171 cc = FSR_CC_EQ; 172 else 173 cc = diff(FSR_CC_GT); 174 175 done: 176 fe->fe_fsr = (fe->fe_fsr & fcc_nmask[fcc]) | 177 ((u_long)cc << fcc_shift[fcc]); 178 } 179