arch/mips/math-emu/dp_sub.c

   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 }