LXR linux/arch/mips/math-emu/dp

   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
  12union 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