1 /* $NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $ */ 2 3 /* 4 * Copyright (c) 1995 Ken Nakata 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the author nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * @(#)fpu_rem.c 10/24/95 32 */ 33 34 #include <sys/cdefs.h> 35 __KERNEL_RCSID(0, "$NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $"); 36 37 #include <sys/types.h> 38 #include <sys/signal.h> 39 #include <machine/frame.h> 40 41 #include "fpu_emulate.h" 42 43 /* 44 * ALGORITHM 45 * 46 * Step 1. Save and strip signs of X and Y: signX := sign(X), 47 * signY := sign(Y), X := *X*, Y := *Y*, 48 * signQ := signX EOR signY. Record whether MOD or REM 49 * is requested. 50 * 51 * Step 2. Set L := expo(X)-expo(Y), Q := 0. 52 * If (L < 0) then 53 * R := X, go to Step 4. 54 * else 55 * R := 2^(-L)X, j := L. 56 * endif 57 * 58 * Step 3. Perform MOD(X,Y) 59 * 3.1 If R = Y, then { Q := Q + 1, R := 0, go to Step 7. } 60 * 3.2 If R > Y, then { R := R - Y, Q := Q + 1} 61 * 3.3 If j = 0, go to Step 4. 62 * 3.4 j := j - 1, Q := 2Q, R := 2R. Go to Step 3.1. 63 * 64 * Step 4. R := signX*R. 65 * 66 * Step 5. If MOD is requested, go to Step 7. 67 * 68 * Step 6. Now, R = MOD(X,Y), convert to REM(X,Y) is requested. 69 * Do banker's rounding. 70 * If abs(R) > Y/2 71 * || (abs(R) == Y/2 && Q % 2 == 1) then 72 * { Q := Q + 1, R := R - signX * Y }. 73 * 74 * Step 7. Return signQ, last 7 bits of Q, and R as required. 75 */ 76 77 static struct fpn * __fpu_modrem(struct fpemu *fe, int is_mod); 78 static int abscmp3(const struct fpn *a, const struct fpn *b); 79 80 /* Absolute FORTRAN Compare */ 81 static int 82 abscmp3(const struct fpn *a, const struct fpn *b) 83 { 84 int i; 85 86 if (a->fp_exp < b->fp_exp) { 87 return -1; 88 } else if (a->fp_exp > b->fp_exp) { 89 return 1; 90 } else { 91 for (i = 0; i < 3; i++) { 92 if (a->fp_mant[i] < b->fp_mant[i]) 93 return -1; 94 else if (a->fp_mant[i] > b->fp_mant[i]) 95 return 1; 96 } 97 } 98 return 0; 99 } 100 101 static struct fpn * 102 __fpu_modrem(struct fpemu *fe, int is_mod) 103 { 104 static struct fpn X, Y; 105 struct fpn *x, *y, *r; 106 uint32_t signX, signY, signQ; 107 int j, l, q; 108 int cmp; 109 110 if (ISNAN(&fe->fe_f1) || ISNAN(&fe->fe_f2)) 111 return fpu_newnan(fe); 112 if (ISINF(&fe->fe_f1) || ISZERO(&fe->fe_f2)) 113 return fpu_newnan(fe); 114 115 CPYFPN(&X, &fe->fe_f1); 116 CPYFPN(&Y, &fe->fe_f2); 117 x = &X; 118 y = &Y; 119 q = 0; 120 r = &fe->fe_f2; 121 122 /* 123 * Step 1 124 */ 125 signX = x->fp_sign; 126 signY = y->fp_sign; 127 signQ = (signX ^ signY); 128 x->fp_sign = y->fp_sign = 0; 129 130 /* Special treatment that just return input value but Q is necessary */ 131 if (ISZERO(x) || ISINF(y)) { 132 r = &fe->fe_f1; 133 goto Step7; 134 } 135 136 /* 137 * Step 2 138 */ 139 l = x->fp_exp - y->fp_exp; 140 CPYFPN(r, x); 141 if (l >= 0) { 142 r->fp_exp -= l; 143 j = l; 144 145 /* 146 * Step 3 147 */ 148 for (;;) { 149 cmp = abscmp3(r, y); 150 151 /* Step 3.1 */ 152 if (cmp == 0) 153 break; 154 155 /* Step 3.2 */ 156 if (cmp > 0) { 157 CPYFPN(&fe->fe_f1, r); 158 CPYFPN(&fe->fe_f2, y); 159 fe->fe_f2.fp_sign = 1; 160 r = fpu_add(fe); 161 q++; 162 } 163 164 /* Step 3.3 */ 165 if (j == 0) 166 goto Step4; 167 168 /* Step 3.4 */ 169 j--; 170 q += q; 171 r->fp_exp++; 172 } 173 /* R == Y */ 174 q++; 175 r->fp_class = FPC_ZERO; 176 goto Step7; 177 } 178 Step4: 179 r->fp_sign = signX; 180 181 /* 182 * Step 5 183 */ 184 if (is_mod) 185 goto Step7; 186 187 /* 188 * Step 6 189 */ 190 /* y = y / 2 */ 191 y->fp_exp--; 192 /* abscmp3 ignore sign */ 193 cmp = abscmp3(r, y); 194 /* revert y */ 195 y->fp_exp++; 196 197 if (cmp > 0 || (cmp == 0 && q % 2)) { 198 q++; 199 CPYFPN(&fe->fe_f1, r); 200 CPYFPN(&fe->fe_f2, y); 201 fe->fe_f2.fp_sign = !signX; 202 r = fpu_add(fe); 203 } 204 205 /* 206 * Step 7 207 */ 208 Step7: 209 q &= 0x7f; 210 q |= (signQ << 7); 211 fe->fe_fpframe->fpf_fpsr = 212 fe->fe_fpsr = 213 (fe->fe_fpsr & ~FPSR_QTT) | (q << 16); 214 return r; 215 } 216 217 struct fpn * 218 fpu_rem(struct fpemu *fe) 219 { 220 return __fpu_modrem(fe, 0); 221 } 222 223 struct fpn * 224 fpu_mod(struct fpemu *fe) 225 { 226 return __fpu_modrem(fe, 1); 227 } 228
Indexes created Wed Sep 24 05:09:52 GMT 2025