1 /* IEEE754 floating point arithmetic 2 * single precision 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 "ieee754sp.h" 28 29 ieee754sp ieee754sp_sub(ieee754sp x, ieee754sp y) 30 { 31 COMPXSP; 32 COMPYSP; 33 34 EXPLODEXSP; 35 EXPLODEYSP; 36 37 CLEARCX; 38 39 FLUSHXSP; 40 FLUSHYSP; 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 ieee754sp_nanxcpt(ieee754sp_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 ieee754sp_xcpt(ieee754sp_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 ieee754sp_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 ieee754sp_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 SPDNORMX; 112 113 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): 114 SPDNORMY; 115 break; 116 117 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): 118 SPDNORMX; 119 break; 120 121 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): 122 break; 123 } 124 /* flip sign of y and handle as add */ 125 ys ^= 1; 126 127 assert(xm & SP_HIDDEN_BIT); 128 assert(ym & SP_HIDDEN_BIT); 129 130 131 /* provide guard,round and stick bit space */ 132 xm <<= 3; 133 ym <<= 3; 134 135 if (xe > ye) { 136 /* have to shift y fraction right to align 137 */ 138 int s = xe - ye; 139 SPXSRSYn(s); 140 } else if (ye > xe) { 141 /* have to shift x fraction right to align 142 */ 143 int s = ye - xe; 144 SPXSRSXn(s); 145 } 146 assert(xe == ye); 147 assert(xe <= SP_EMAX); 148 149 if (xs == ys) { 150 /* generate 28 bit result of adding two 27 bit numbers 151 */ 152 xm = xm + ym; 153 xe = xe; 154 xs = xs; 155 156 if (xm >> (SP_MBITS + 1 + 3)) { /* carry out */ 157 SPXSRSX1(); /* shift preserving sticky */ 158 } 159 } else { 160 if (xm >= ym) { 161 xm = xm - ym; 162 xe = xe; 163 xs = xs; 164 } else { 165 xm = ym - xm; 166 xe = xe; 167 xs = ys; 168 } 169 if (xm == 0) { 170 if (ieee754_csr.rm == IEEE754_RD) 171 return ieee754sp_zero(1); /* round negative inf. => sign = -1 */ 172 else 173 return ieee754sp_zero(0); /* other round modes => sign = 1 */ 174 } 175 /* normalize to rounding precision 176 */ 177 while ((xm >> (SP_MBITS + 3)) == 0) { 178 xm <<= 1; 179 xe--; 180 } 181 } 182 SPNORMRET2(xs, xe, xm, "sub", x, y); 183 } 184