fpu_rem.c revision 1.8
1 /* $NetBSD: fpu_rem.c,v 1.8 2009/03/14 15:36:09 dsl 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 1.8 2009/03/14 15:36:09 dsl 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), k := 0, 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, go to Step 9. 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 k := k + 1, j := j - 1, Q := 2Q, R := 2R. Go to 63 * Step 3.1. 64 * 65 * Step 4. At this point, R = X - QY = MOD(X,Y). Set 66 * Last_Subtract := false (used in Step 7 below). If 67 * MOD is requested, go to Step 6. 68 * 69 * Step 5. R = MOD(X,Y), but REM(X,Y) is requested. 70 * 5.1 If R < Y/2, then R = MOD(X,Y) = REM(X,Y). Go to 71 * Step 6. 72 * 5.2 If R > Y/2, then { set Last_Subtract := true, 73 * Q := Q + 1, Y := signY*Y }. Go to Step 6. 74 * 5.3 This is the tricky case of R = Y/2. If Q is odd, 75 * then { Q := Q + 1, signX := -signX }. 76 * 77 * Step 6. R := signX*R. 78 * 79 * Step 7. If Last_Subtract = true, R := R - Y. 80 * 81 * Step 8. Return signQ, last 7 bits of Q, and R as required. 82 * 83 * Step 9. At this point, R = 2^(-j)*X - Q Y = Y. Thus, 84 * X = 2^(j)*(Q+1)Y. set Q := 2^(j)*(Q+1), 85 * R := 0. Return signQ, last 7 bits of Q, and R. 86 */ 87 88 static struct fpn * __fpu_modrem(struct fpemu *fe, int modrem); 89 90 static struct fpn * 91 __fpu_modrem(fe, modrem) 92 struct fpemu *fe; 93 int modrem; 94 { 95 static struct fpn X, Y; 96 struct fpn *x, *y, *r; 97 u_int signX, signY, signQ; 98 int j, k, l, q; 99 int Last_Subtract; 100 101 CPYFPN(&X, &fe->fe_f1); 102 CPYFPN(&Y, &fe->fe_f2); 103 x = &X; 104 y = &Y; 105 r = &fe->fe_f2; 106 107 /* 108 * Step 1 109 */ 110 signX = x->fp_sign; 111 signY = y->fp_sign; 112 signQ = (signX ^ signY); 113 x->fp_sign = y->fp_sign = 0; 114 115 /* 116 * Step 2 117 */ 118 l = x->fp_exp - y->fp_exp; 119 k = 0; 120 q = 0; 121 if (l >= 0) { 122 CPYFPN(r, x); 123 r->fp_exp -= l; 124 j = l; 125 126 /* 127 * Step 3 128 */ 129 while (y->fp_exp != r->fp_exp || y->fp_mant[0] != r->fp_mant[0] || 130 y->fp_mant[1] != r->fp_mant[1] || 131 y->fp_mant[2] != r->fp_mant[2]) { 132 133 /* Step 3.2 */ 134 if (y->fp_exp < r->fp_exp || y->fp_mant[0] < r->fp_mant[0] || 135 y->fp_mant[1] < r->fp_mant[1] || 136 y->fp_mant[2] < r->fp_mant[2]) { 137 CPYFPN(&fe->fe_f1, r); 138 CPYFPN(&fe->fe_f2, y); 139 fe->fe_f2.fp_sign = 1; 140 r = fpu_add(fe); 141 q++; 142 } 143 144 /* Step 3.3 */ 145 if (j == 0) 146 goto Step4; 147 148 /* Step 3.4 */ 149 k++; 150 j--; 151 q += q; 152 r->fp_exp++; 153 } 154 /* Step 9 */ 155 goto Step9; 156 } 157 Step4: 158 Last_Subtract = 0; 159 if (modrem == 0) 160 goto Step6; 161 162 /* 163 * Step 5 164 */ 165 /* Step 5.1 */ 166 if (r->fp_exp + 1 < y->fp_exp || 167 (r->fp_exp + 1 == y->fp_exp && 168 (r->fp_mant[0] < y->fp_mant[0] || r->fp_mant[1] < y->fp_mant[1] || 169 r->fp_mant[2] < y->fp_mant[2]))) 170 /* if r < y/2 */ 171 goto Step6; 172 /* Step 5.2 */ 173 if (r->fp_exp + 1 != y->fp_exp || 174 r->fp_mant[0] != y->fp_mant[0] || r->fp_mant[1] != y->fp_mant[1] || 175 r->fp_mant[2] != y->fp_mant[2]) { 176 /* if (!(r < y/2) && !(r == y/2)) */ 177 Last_Subtract = 1; 178 q++; 179 y->fp_sign = signY; 180 } else { 181 /* Step 5.3 */ 182 /* r == y/2 */ 183 if (q % 2) { 184 q++; 185 signX = !signX; 186 } 187 } 188 189 Step6: 190 r->fp_sign = signX; 191 192 /* 193 * Step 7 194 */ 195 if (Last_Subtract) { 196 CPYFPN(&fe->fe_f1, r); 197 CPYFPN(&fe->fe_f2, y); 198 fe->fe_f2.fp_sign = !y->fp_sign; 199 r = fpu_add(fe); 200 } 201 /* 202 * Step 8 203 */ 204 q &= 0x7f; 205 q |= (signQ << 7); 206 fe->fe_fpframe->fpf_fpsr = 207 fe->fe_fpsr = 208 (fe->fe_fpsr & ~FPSR_QTT) | (q << 16); 209 return r; 210 211 Step9: 212 fe->fe_f1.fp_class = FPC_ZERO; 213 q++; 214 q &= 0x7f; 215 q |= (signQ << 7); 216 fe->fe_fpframe->fpf_fpsr = 217 fe->fe_fpsr = 218 (fe->fe_fpsr & ~FPSR_QTT) | (q << 16); 219 return &fe->fe_f1; 220 } 221 222 struct fpn * 223 fpu_rem(struct fpemu *fe) 224 { 225 return __fpu_modrem(fe, 1); 226 } 227 228 struct fpn * 229 fpu_mod(struct fpemu *fe) 230 { 231 return __fpu_modrem(fe, 0); 232 } 233
Indexes created Tue Sep 30 11:09:46 GMT 2025