// 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_div(union ieee754dp x, union ieee754dp y)
{
        u64 rm;
        int re;
        u64 bm;

        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):
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754dp_indef();

        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
                return ieee754dp_zero(xs ^ ys);

        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 ieee754dp_inf(xs ^ ys);

        /*
         * Zero handling
         */
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
                ieee754_setcx(IEEE754_INVALID_OPERATION);
                return ieee754dp_indef();

        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
                ieee754_setcx(IEEE754_ZERO_DIVIDE);
                return ieee754dp_inf(xs ^ ys);

        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
                return ieee754dp_zero(xs == ys ? 0 : 1);

        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
                DPDNORMX;
                fallthrough;
        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
                DPDNORMY;
                break;

        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
                DPDNORMX;
                break;

        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
                break;
        }
        assert(xm & DP_HIDDEN_BIT);
        assert(ym & DP_HIDDEN_BIT);

        /* provide rounding space */
        xm <<= 3;
        ym <<= 3;

        /* now the dirty work */

        rm = 0;
        re = xe - ye;

        for (bm = DP_MBIT(DP_FBITS + 2); bm; bm >>= 1) {
                if (xm >= ym) {
                        xm -= ym;
                        rm |= bm;
                        if (xm == 0)
                                break;
                }
                xm <<= 1;
        }

        rm <<= 1;
        if (xm)
                rm |= 1;        /* have remainder, set sticky */

        assert(rm);

        /*
         * Normalise rm to rounding precision ?
         */
        while ((rm >> (DP_FBITS + 3)) == 0) {
                rm <<= 1;
                re--;
        }

        return ieee754dp_format(xs == ys ? 0 : 1, re, rm);
}