fpu_rem.c revision 1.2
1 /* $NetBSD: fpu_rem.c,v 1.2 1996/04/30 11:52:36 briggs 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/types.h> 35 #include <sys/signal.h> 36 #include <machine/frame.h> 37 38 #include "fpu_emulate.h" 39 40 /* 41 * ALGORITHM 42 * 43 * Step 1. Save and strip signs of X and Y: signX := sign(X), 44 * signY := sign(Y), X := *X*, Y := *Y*, 45 * signQ := signX EOR signY. Record whether MOD or REM 46 * is requested. 47 * 48 * Step 2. Set L := expo(X)-expo(Y), k := 0, Q := 0. 49 * If (L < 0) then 50 * R := X, go to Step 4. 51 * else 52 * R := 2^(-L)X, j := L. 53 * endif 54 * 55 * Step 3. Perform MOD(X,Y) 56 * 3.1 If R = Y, go to Step 9. 57 * 3.2 If R > Y, then { R := R - Y, Q := Q + 1} 58 * 3.3 If j = 0, go to Step 4. 59 * 3.4 k := k + 1, j := j - 1, Q := 2Q, R := 2R. Go to 60 * Step 3.1. 61 * 62 * Step 4. At this point, R = X - QY = MOD(X,Y). Set 63 * Last_Subtract := false (used in Step 7 below). If 64 * MOD is requested, go to Step 6. 65 * 66 * Step 5. R = MOD(X,Y), but REM(X,Y) is requested. 67 * 5.1 If R < Y/2, then R = MOD(X,Y) = REM(X,Y). Go to 68 * Step 6. 69 * 5.2 If R > Y/2, then { set Last_Subtract := true, 70 * Q := Q + 1, Y := signY*Y }. Go to Step 6. 71 * 5.3 This is the tricky case of R = Y/2. If Q is odd, 72 * then { Q := Q + 1, signX := -signX }. 73 * 74 * Step 6. R := signX*R. 75 * 76 * Step 7. If Last_Subtract = true, R := R - Y. 77 * 78 * Step 8. Return signQ, last 7 bits of Q, and R as required. 79 * 80 * Step 9. At this point, R = 2^(-j)*X - Q Y = Y. Thus, 81 * X = 2^(j)*(Q+1)Y. set Q := 2^(j)*(Q+1), 82 * R := 0. Return signQ, last 7 bits of Q, and R. 83 */ 84 85 static struct fpn * __fpu_modrem __P((struct fpemu *fe, int modrem)); 86 87 static struct fpn * 88 __fpu_modrem(fe, modrem) 89 struct fpemu *fe; 90 int modrem; 91 { 92 static struct fpn X, Y; 93 struct fpn *x, *y, *r; 94 u_int signX, signY, signQ; 95 int j, k, l, q; 96 int Last_Subtract; 97 98 CPYFPN(&X, &fe->fe_f1); 99 CPYFPN(&Y, &fe->fe_f2); 100 x = &X; 101 y = &Y; 102 r = &fe->fe_f2; 103 104 /* 105 * Step 1 106 */ 107 signX = x->fp_sign; 108 signY = y->fp_sign; 109 signQ = (signX ^ signY); 110 x->fp_sign = y->fp_sign = 0; 111 112 /* 113 * Step 2 114 */ 115 l = x->fp_exp - y->fp_exp; 116 k = 0; 117 q = 0; 118 if (l < 0) { 119 goto Step4; 120 } else { 121 CPYFPN(r, x); 122 r->fp_exp -= l; 123 j = l; 124 125 /* 126 * Step 3 127 */ 128 while (y->fp_exp != r->fp_exp || y->fp_mant[0] != r->fp_mant[0] || 129 y->fp_mant[1] != r->fp_mant[1] || 130 y->fp_mant[2] != r->fp_mant[2] || 131 y->fp_mant[3] != r->fp_mant[3]) { 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 y->fp_mant[3] < r->fp_mant[3]) { 138 CPYFPN(&fe->fe_f1, r); 139 CPYFPN(&fe->fe_f2, y); 140 fe->fe_f2.fp_sign = 1; 141 r = fpu_add(fe); 142 q++; 143 } 144 145 /* Step 3.3 */ 146 if (j == 0) 147 goto Step4; 148 149 /* Step 3.4 */ 150 k++; 151 j--; 152 q += q; 153 r->fp_exp++; 154 } 155 } 156 Step4: 157 Last_Subtract = 0; 158 if (modrem == 0) 159 goto Step6; 160 161 /* 162 * Step 5 163 */ 164 /* Step 5.1 */ 165 if (r->fp_exp + 1 < y->fp_exp || 166 (r->fp_exp + 1 == y->fp_exp && 167 (r->fp_mant[0] < y->fp_mant[0] || r->fp_mant[1] < y->fp_mant[1] || 168 r->fp_mant[2] < y->fp_mant[3] || r->fp_mant[4] < y->fp_mant[4]))) 169 /* if r < y/2 */ 170 goto Step6; 171 /* Step 5.2 */ 172 if (r->fp_exp + 1 != y->fp_exp || 173 r->fp_mant[0] != y->fp_mant[0] || r->fp_mant[1] != y->fp_mant[1] || 174 r->fp_mant[2] != y->fp_mant[2] || r->fp_mant[3] != y->fp_mant[3]) { 175 /* if (!(r < y/2) && !(r == y/2)) */ 176 Last_Subtract = 1; 177 q++; 178 y->fp_sign = signY; 179 } else { 180 /* Step 5.3 */ 181 /* r == y/2 */ 182 if (q % 2) { 183 q++; 184 signX = !signX; 185 } 186 } 187 188 Step6: 189 r->fp_sign = signX; 190 191 /* 192 * Step 7 193 */ 194 if (Last_Subtract) { 195 CPYFPN(&fe->fe_f1, r); 196 CPYFPN(&fe->fe_f2, y); 197 fe->fe_f2.fp_sign = !y->fp_sign; 198 r = fpu_add(fe); 199 } 200 /* 201 * Step 8 202 */ 203 q &= 0x7f; 204 q |= (signQ << 7); 205 fe->fe_fpframe->fpf_fpsr = 206 fe->fe_fpsr = 207 (fe->fe_fpsr & ~FPSR_QTT) | (q << 16); 208 return r; 209 } 210 211 struct fpn * 212 fpu_rem(fe) 213 struct fpemu *fe; 214 { 215 return __fpu_modrem(fe, 1); 216 } 217 218 struct fpn * 219 fpu_mod(fe) 220 struct fpemu *fe; 221 { 222 return __fpu_modrem(fe, 0); 223 } 224
Indexes created Tue Sep 30 11:09:46 GMT 2025