1 /* IEEE754 floating point arithmetic 2 * double precision: common utilities 3 */ 4 /* 5 * MIPS floating point support 6 * Copyright (C) 1994-2000 Algorithmics Ltd. 7 * http://www.algor.co.uk 8 * 9 * ######################################################################## 10 * 11 * This program is free software; you can distribute it and/or modify it 12 * under the terms of the GNU General Public License (Version 2) as 13 * published by the Free Software Foundation. 14 * 15 * This program is distributed in the hope it will be useful, but WITHOUT 16 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 17 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 18 * for more details. 19 * 20 * You should have received a copy of the GNU General Public License along 21 * with this program; if not, write to the Free Software Foundation, Inc., 22 * 59 Temple Place - Suite 330, Boston MA 02111-1307, USA. 23 * 24 * ######################################################################## 25 */ 26 27 28 #include "ieee754dp.h" 29 30 ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y) 31 { 32 COMPXDP; 33 COMPYDP; 34 35 EXPLODEXDP; 36 EXPLODEYDP; 37 38 CLEARCX; 39 40 FLUSHXDP; 41 FLUSHYDP; 42 43 switch (CLPAIR(xc, yc)) { 44 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): 45 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): 46 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): 47 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): 48 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): 49 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): 50 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): 51 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): 52 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): 53 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): 54 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): 55 SETCX(IEEE754_INVALID_OPERATION); 56 return ieee754dp_nanxcpt(ieee754dp_indef(), "sub", x, y); 57 58 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): 59 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): 60 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): 61 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): 62 return y; 63 64 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): 65 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): 66 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): 67 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): 68 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): 69 return x; 70 71 72 /* Infinity handling 73 */ 74 75 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): 76 if (xs != ys) 77 return x; 78 SETCX(IEEE754_INVALID_OPERATION); 79 return ieee754dp_xcpt(ieee754dp_indef(), "sub", x, y); 80 81 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): 82 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): 83 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): 84 return ieee754dp_inf(ys ^ 1); 85 86 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): 87 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): 88 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): 89 return x; 90 91 /* Zero handling 92 */ 93 94 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): 95 if (xs != ys) 96 return x; 97 else 98 return ieee754dp_zero(ieee754_csr.rm == 99 IEEE754_RD); 100 101 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): 102 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): 103 return x; 104 105 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): 106 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): 107 /* quick fix up */ 108 DPSIGN(y) ^= 1; 109 return y; 110 111 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): 112 DPDNORMX; 113 /* FALL THROUGH */ 114 115 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): 116 /* normalize ym,ye */ 117 DPDNORMY; 118 break; 119 120 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): 121 /* normalize xm,xe */ 122 DPDNORMX; 123 break; 124 125 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): 126 break; 127 } 128 /* flip sign of y and handle as add */ 129 ys ^= 1; 130 131 assert(xm & DP_HIDDEN_BIT); 132 assert(ym & DP_HIDDEN_BIT); 133 134 135 /* provide guard,round and stick bit dpace */ 136 xm <<= 3; 137 ym <<= 3; 138 139 if (xe > ye) { 140 /* have to shift y fraction right to align 141 */ 142 int s = xe - ye; 143 ym = XDPSRS(ym, s); 144 ye += s; 145 } else if (ye > xe) { 146 /* have to shift x fraction right to align 147 */ 148 int s = ye - xe; 149 xm = XDPSRS(xm, s); 150 xe += s; 151 } 152 assert(xe == ye); 153 assert(xe <= DP_EMAX); 154 155 if (xs == ys) { 156 /* generate 28 bit result of adding two 27 bit numbers 157 */ 158 xm = xm + ym; 159 xe = xe; 160 xs = xs; 161 162 if (xm >> (DP_MBITS + 1 + 3)) { /* carry out */ 163 xm = XDPSRS1(xm); /* shift preserving sticky */ 164 xe++; 165 } 166 } else { 167 if (xm >= ym) { 168 xm = xm - ym; 169 xe = xe; 170 xs = xs; 171 } else { 172 xm = ym - xm; 173 xe = xe; 174 xs = ys; 175 } 176 if (xm == 0) { 177 if (ieee754_csr.rm == IEEE754_RD) 178 return ieee754dp_zero(1); /* round negative inf. => sign = -1 */ 179 else 180 return ieee754dp_zero(0); /* other round modes => sign = 1 */ 181 } 182 183 /* normalize to rounding precision 184 */ 185 while ((xm >> (DP_MBITS + 3)) == 0) { 186 xm <<= 1; 187 xe--; 188 } 189 } 190 DPNORMRET2(xs, xe, xm, "sub", x, y); 191 } 192