1 // SPDX-License-Identifier: GPL-2.0-only 2 /* IEEE754 floating point arithmetic 3 * double precision: common utilities 4 */ 5 /* 6 * MIPS floating point support 7 * Copyright (C) 1994-2000 Algorithmics Ltd. 8 */ 9 10 #include "ieee754dp.h" 11 12 union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y) 13 { 14 int s; 15 16 COMPXDP; 17 COMPYDP; 18 19 EXPLODEXDP; 20 EXPLODEYDP; 21 22 ieee754_clearcx(); 23 24 FLUSHXDP; 25 FLUSHYDP; 26 27 switch (CLPAIR(xc, yc)) { 28 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN): 29 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN): 30 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN): 31 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN): 32 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN): 33 return ieee754dp_nanxcpt(y); 34 35 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN): 36 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN): 37 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO): 38 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM): 39 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM): 40 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF): 41 return ieee754dp_nanxcpt(x); 42 43 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN): 44 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN): 45 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN): 46 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN): 47 return y; 48 49 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN): 50 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO): 51 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM): 52 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM): 53 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF): 54 return x; 55 56 57 /* 58 * Infinity handling 59 */ 60 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF): 61 if (xs != ys) 62 return x; 63 ieee754_setcx(IEEE754_INVALID_OPERATION); 64 return ieee754dp_indef(); 65 66 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF): 67 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF): 68 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF): 69 return ieee754dp_inf(ys ^ 1); 70 71 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO): 72 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM): 73 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM): 74 return x; 75 76 /* 77 * Zero handling 78 */ 79 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO): 80 if (xs != ys) 81 return x; 82 else 83 return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD); 84 85 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO): 86 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO): 87 return x; 88 89 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM): 90 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM): 91 /* quick fix up */ 92 DPSIGN(y) ^= 1; 93 return y; 94 95 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): 96 DPDNORMX; 97 fallthrough; 98 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): 99 /* normalize ym,ye */ 100 DPDNORMY; 101 break; 102 103 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): 104 /* normalize xm,xe */ 105 DPDNORMX; 106 break; 107 108 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): 109 break; 110 } 111 /* flip sign of y and handle as add */ 112 ys ^= 1; 113 114 assert(xm & DP_HIDDEN_BIT); 115 assert(ym & DP_HIDDEN_BIT); 116 117 118 /* provide guard,round and stick bit dpace */ 119 xm <<= 3; 120 ym <<= 3; 121 122 if (xe > ye) { 123 /* 124 * Have to shift y fraction right to align 125 */ 126 s = xe - ye; 127 ym = XDPSRS(ym, s); 128 ye += s; 129 } else if (ye > xe) { 130 /* 131 * Have to shift x fraction right to align 132 */ 133 s = ye - xe; 134 xm = XDPSRS(xm, s); 135 xe += s; 136 } 137 assert(xe == ye); 138 assert(xe <= DP_EMAX); 139 140 if (xs == ys) { 141 /* generate 28 bit result of adding two 27 bit numbers 142 */ 143 xm = xm + ym; 144 145 if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */ 146 xm = XDPSRS1(xm); /* shift preserving sticky */ 147 xe++; 148 } 149 } else { 150 if (xm >= ym) { 151 xm = xm - ym; 152 } else { 153 xm = ym - xm; 154 xs = ys; 155 } 156 if (xm == 0) { 157 if (ieee754_csr.rm == FPU_CSR_RD) 158 return ieee754dp_zero(1); /* round negative inf. => sign = -1 */ 159 else 160 return ieee754dp_zero(0); /* other round modes => sign = 1 */ 161 } 162 163 /* normalize to rounding precision 164 */ 165 while ((xm >> (DP_FBITS + 3)) == 0) { 166 xm <<= 1; 167 xe--; 168 } 169 } 170 171 return ieee754dp_format(xs, xe, xm); 172 } 173