arch/mips/math-emu/sp_sub.c

   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                 fallthrough;
  98         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
  99                 SPDNORMY;
 100                 break;
 101
 102         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
 103                 SPDNORMX;
 104                 break;
 105
 106         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
 107                 break;
 108         }
 109         /* flip sign of y and handle as add */
 110         ys ^= 1;
 111
 112         assert(xm & SP_HIDDEN_BIT);
 113         assert(ym & SP_HIDDEN_BIT);
 114
 115
 116         /* provide guard,round and stick bit space */
 117         xm <<= 3;
 118         ym <<= 3;
 119
 120         if (xe > ye) {
 121                 /*
 122                  * have to shift y fraction right to align
 123                  */
 124                 s = xe - ye;
 125                 ym = XSPSRS(ym, s);
 126                 ye += s;
 127         } else if (ye > xe) {
 128                 /*
 129                  * have to shift x fraction right to align
 130                  */
 131                 s = ye - xe;
 132                 xm = XSPSRS(xm, s);
 133                 xe += s;
 134         }
 135         assert(xe == ye);
 136         assert(xe <= SP_EMAX);
 137
 138         if (xs == ys) {
 139                 /* generate 28 bit result of adding two 27 bit numbers
 140                  */
 141                 xm = xm + ym;
 142
 143                 if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */
 144                         SPXSRSX1();     /* shift preserving sticky */
 145                 }
 146         } else {
 147                 if (xm >= ym) {
 148                         xm = xm - ym;
 149                 } else {
 150                         xm = ym - xm;
 151                         xs = ys;
 152                 }
 153                 if (xm == 0) {
 154                         if (ieee754_csr.rm == FPU_CSR_RD)
 155                                 return ieee754sp_zero(1);       /* round negative inf. => sign = -1 */
 156                         else
 157                                 return ieee754sp_zero(0);       /* other round modes   => sign = 1 */
 158                 }
 159                 /* normalize to rounding precision
 160                  */
 161                 while ((xm >> (SP_FBITS + 3)) == 0) {
 162                         xm <<= 1;
 163                         xe--;
 164                 }
 165         }
 166
 167         return ieee754sp_format(xs, xe, xm);
 168 }