1 /* IEEE754 floating point arithmetic 2 * single precision 3 */ 4 /* 5 * MIPS floating point support 6 * Copyright (C) 1994-2000 Algorithmics Ltd. 7 * 8 * This program is free software; you can distribute it and/or modify it 9 * under the terms of the GNU General Public License (Version 2) as 10 * published by the Free Software Foundation. 11 * 12 * This program is distributed in the hope it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * for more details. 16 * 17 * You should have received a copy of the GNU General Public License along 18 * with this program; if not, write to the Free Software Foundation, Inc., 19 * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 */ 21 22 #include "ieee754sp.h" 23 24 union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y) 25 { 26 int s; 27 28 COMPXSP; 29 COMPYSP; 30 31 EXPLODEXSP; 32 EXPLODEYSP; 33 34 ieee754_clearcx(); 35 36 FLUSHXSP; 37 FLUSHYSP; 38 39 switch (CLPAIR(xc, yc)) { 40 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): 41 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): 42 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): 43 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): 44 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): 45 return ieee754sp_nanxcpt(y); 46 47 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): 48 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): 49 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): 50 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): 51 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): 52 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): 53 return ieee754sp_nanxcpt(x); 54 55 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): 56 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): 57 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): 58 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): 59 return y; 60 61 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): 62 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): 63 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): 64 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): 65 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): 66 return x; 67 68 69 /* 70 * Infinity handling 71 */ 72 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): 73 if (xs != ys) 74 return x; 75 ieee754_setcx(IEEE754_INVALID_OPERATION); 76 return ieee754sp_indef(); 77 78 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): 79 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): 80 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): 81 return ieee754sp_inf(ys ^ 1); 82 83 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): 84 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): 85 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): 86 return x; 87 88 /* 89 * Zero handling 90 */ 91 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): 92 if (xs != ys) 93 return x; 94 else 95 return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD); 96 97 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): 98 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): 99 return x; 100 101 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): 102 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): 103 /* quick fix up */ 104 SPSIGN(y) ^= 1; 105 return y; 106 107 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): 108 SPDNORMX; 109 /* fall through */ 110 111 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): 112 SPDNORMY; 113 break; 114 115 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): 116 SPDNORMX; 117 break; 118 119 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): 120 break; 121 } 122 /* flip sign of y and handle as add */ 123 ys ^= 1; 124 125 assert(xm & SP_HIDDEN_BIT); 126 assert(ym & SP_HIDDEN_BIT); 127 128 129 /* provide guard,round and stick bit space */ 130 xm <<= 3; 131 ym <<= 3; 132 133 if (xe > ye) { 134 /* 135 * have to shift y fraction right to align 136 */ 137 s = xe - ye; 138 ym = XSPSRS(ym, s); 139 ye += s; 140 } else if (ye > xe) { 141 /* 142 * have to shift x fraction right to align 143 */ 144 s = ye - xe; 145 xm = XSPSRS(xm, s); 146 xe += s; 147 } 148 assert(xe == ye); 149 assert(xe <= SP_EMAX); 150 151 if (xs == ys) { 152 /* generate 28 bit result of adding two 27 bit numbers 153 */ 154 xm = xm + ym; 155 156 if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */ 157 SPXSRSX1(); /* shift preserving sticky */ 158 } 159 } else { 160 if (xm >= ym) { 161 xm = xm - ym; 162 } else { 163 xm = ym - xm; 164 xs = ys; 165 } 166 if (xm == 0) { 167 if (ieee754_csr.rm == FPU_CSR_RD) 168 return ieee754sp_zero(1); /* round negative inf. => sign = -1 */ 169 else 170 return ieee754sp_zero(0); /* other round modes => sign = 1 */ 171 } 172 /* normalize to rounding precision 173 */ 174 while ((xm >> (SP_FBITS + 3)) == 0) { 175 xm <<= 1; 176 xe--; 177 } 178 } 179 180 return ieee754sp_format(xs, xe, xm); 181 } 182