1 // SPDX-License-Identifier: GPL-2.0-only 2 /* IEEE754 floating point arithmetic 3 * single precision 4 */ 5 /* 6 * MIPS floating point support 7 * Copyright (C) 1994-2000 Algorithmics Ltd. 8 */ 9 10 #include "ieee754sp.h" 11 12 union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y) 13 { 14 int s; 15 16 COMPXSP; 17 COMPYSP; 18 19 EXPLODEXSP; 20 EXPLODEYSP; 21 22 ieee754_clearcx(); 23 24 FLUSHXSP; 25 FLUSHYSP; 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 ieee754sp_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 ieee754sp_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 ieee754sp_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 ieee754sp_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 ieee754sp_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 SPSIGN(y) ^= 1; 93 return y; 94 95 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM): 96 SPDNORMX; 97 /* fall through */ 98 99 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM): 100 SPDNORMY; 101 break; 102 103 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM): 104 SPDNORMX; 105 break; 106 107 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM): 108 break; 109 } 110 /* flip sign of y and handle as add */ 111 ys ^= 1; 112 113 assert(xm & SP_HIDDEN_BIT); 114 assert(ym & SP_HIDDEN_BIT); 115 116 117 /* provide guard,round and stick bit space */ 118 xm <<= 3; 119 ym <<= 3; 120 121 if (xe > ye) { 122 /* 123 * have to shift y fraction right to align 124 */ 125 s = xe - ye; 126 ym = XSPSRS(ym, s); 127 ye += s; 128 } else if (ye > xe) { 129 /* 130 * have to shift x fraction right to align 131 */ 132 s = ye - xe; 133 xm = XSPSRS(xm, s); 134 xe += s; 135 } 136 assert(xe == ye); 137 assert(xe <= SP_EMAX); 138 139 if (xs == ys) { 140 /* generate 28 bit result of adding two 27 bit numbers 141 */ 142 xm = xm + ym; 143 144 if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */ 145 SPXSRSX1(); /* shift preserving sticky */ 146 } 147 } else { 148 if (xm >= ym) { 149 xm = xm - ym; 150 } else { 151 xm = ym - xm; 152 xs = ys; 153 } 154 if (xm == 0) { 155 if (ieee754_csr.rm == FPU_CSR_RD) 156 return ieee754sp_zero(1); /* round negative inf. => sign = -1 */ 157 else 158 return ieee754sp_zero(0); /* other round modes => sign = 1 */ 159 } 160 /* normalize to rounding precision 161 */ 162 while ((xm >> (SP_FBITS + 3)) == 0) { 163 xm <<= 1; 164 xe--; 165 } 166 } 167 168 return ieee754sp_format(xs, xe, xm); 169 } 170