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