// SPDX-License-Identifier: GPL-2.0-only
/* IEEE754 floating point arithmetic
 * double precision: common utilities
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 */

#include "ieee754dp.h"

union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y)
{
        int s;

        COMPXDP;
        COMPYDP;

        EXPLODEXDP;
        EXPLODEYDP;

        ieee754_clearcx();

        FLUSHXDP;
        FLUSHYDP;

        switch (CLPAIR(xc, yc)) {
        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
                return ieee754dp_nanxcpt(y);

        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
                return ieee754dp_nanxcpt(x);

        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
                return y;

        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
                return x;


        /*
         * Infinity handling
         */
        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
                if (xs != ys)
                        return x;
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754dp_indef();

        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
                return ieee754dp_inf(ys ^ 1);

        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
                return x;

        /*
         * Zero handling
         */
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
                if (xs != ys)
                        return x;
                else
                        return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);

        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
                return x;

        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
                /* quick fix up */
                DPSIGN(y) ^= 1;
                return y;

        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
                DPDNORMX;
                fallthrough;
        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
                /* normalize ym,ye */
                DPDNORMY;
                break;

        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
                /* normalize xm,xe */
                DPDNORMX;
                break;

        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
                break;
        }
        /* flip sign of y and handle as add */
        ys ^= 1;

        assert(xm & DP_HIDDEN_BIT);
        assert(ym & DP_HIDDEN_BIT);


        /* provide guard,round and stick bit dpace */
        xm <<= 3;
        ym <<= 3;

        if (xe > ye) {
                /*
                 * Have to shift y fraction right to align
                 */
                s = xe - ye;
                ym = XDPSRS(ym, s);
                ye += s;
        } else if (ye > xe) {
                /*
                 * Have to shift x fraction right to align
                 */
                s = ye - xe;
                xm = XDPSRS(xm, s);
                xe += s;
        }
        assert(xe == ye);
        assert(xe <= DP_EMAX);

        if (xs == ys) {
                /* generate 28 bit result of adding two 27 bit numbers
                 */
                xm = xm + ym;

                if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
                        xm = XDPSRS1(xm);       /* shift preserving sticky */
                        xe++;
                }
        } else {
                if (xm >= ym) {
                        xm = xm - ym;
                } else {
                        xm = ym - xm;
                        xs = ys;
                }
                if (xm == 0) {
                        if (ieee754_csr.rm == FPU_CSR_RD)
                                return ieee754dp_zero(1);       /* round negative inf. => sign = -1 */
                        else
                                return ieee754dp_zero(0);       /* other round modes   => sign = 1 */
                }

                /* normalize to rounding precision
                 */
                while ((xm >> (DP_FBITS + 3)) == 0) {
                        xm <<= 1;
                        xe--;
                }
        }

        return ieee754dp_format(xs, xe, xm);
}