mips/math-emu/dp_add.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /* IEEE754 floating point arithmetic
0003  * double precision: common utilities
0004  */
0005 /*
0006  * MIPS floating point support
0007  * Copyright (C) 1994-2000 Algorithmics Ltd.
0008  */
0009
0010 #include "ieee754dp.h"
0011
0012 union ieee754dp ieee754dp_add(union ieee754dp x, union ieee754dp y)
0013 {
0014     int s;
0015
0016     COMPXDP;
0017     COMPYDP;
0018
0019     EXPLODEXDP;
0020     EXPLODEYDP;
0021
0022     ieee754_clearcx();
0023
0024     FLUSHXDP;
0025     FLUSHYDP;
0026
0027     switch (CLPAIR(xc, yc)) {
0028     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
0029     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
0030     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
0031     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
0032     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
0033         return ieee754dp_nanxcpt(y);
0034
0035     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
0036     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
0037     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
0038     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
0039     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
0040     case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
0041         return ieee754dp_nanxcpt(x);
0042
0043     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
0044     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
0045     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
0046     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
0047         return y;
0048
0049     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
0050     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
0051     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
0052     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
0053     case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
0054         return x;
0055
0056
0057     /*
0058      * Infinity handling
0059      */
0060     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
0061         if (xs == ys)
0062             return x;
0063         ieee754_setcx(IEEE754_INVALID_OPERATION);
0064         return ieee754dp_indef();
0065
0066     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
0067     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
0068     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
0069         return y;
0070
0071     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
0072     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
0073     case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
0074         return x;
0075
0076     /*
0077      * Zero handling
0078      */
0079     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
0080         if (xs == ys)
0081             return x;
0082         else
0083             return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
0084
0085     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
0086     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
0087         return x;
0088
0089     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
0090     case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
0091         return y;
0092
0093     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
0094         DPDNORMX;
0095         fallthrough;
0096     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
0097         DPDNORMY;
0098         break;
0099
0100     case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
0101         DPDNORMX;
0102         break;
0103
0104     case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
0105         break;
0106     }
0107     assert(xm & DP_HIDDEN_BIT);
0108     assert(ym & DP_HIDDEN_BIT);
0109
0110     /*
0111      * Provide guard,round and stick bit space.
0112      */
0113     xm <<= 3;
0114     ym <<= 3;
0115
0116     if (xe > ye) {
0117         /*
0118          * Have to shift y fraction right to align.
0119          */
0120         s = xe - ye;
0121         ym = XDPSRS(ym, s);
0122         ye += s;
0123     } else if (ye > xe) {
0124         /*
0125          * Have to shift x fraction right to align.
0126          */
0127         s = ye - xe;
0128         xm = XDPSRS(xm, s);
0129         xe += s;
0130     }
0131     assert(xe == ye);
0132     assert(xe <= DP_EMAX);
0133
0134     if (xs == ys) {
0135         /*
0136          * Generate 28 bit result of adding two 27 bit numbers
0137          * leaving result in xm, xs and xe.
0138          */
0139         xm = xm + ym;
0140
0141         if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
0142             xm = XDPSRS1(xm);
0143             xe++;
0144         }
0145     } else {
0146         if (xm >= ym) {
0147             xm = xm - ym;
0148         } else {
0149             xm = ym - xm;
0150             xs = ys;
0151         }
0152         if (xm == 0)
0153             return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
0154
0155         /*
0156          * Normalize to rounding precision.
0157          */
0158         while ((xm >> (DP_FBITS + 3)) == 0) {
0159             xm <<= 1;
0160             xe--;
0161         }
0162     }
0163
0164     return ieee754dp_format(xs, xe, xm);
0165 }