ieee754sp.c

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/* IEEE754 floating point arithmetic
 * single precision
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 *
 * ########################################################################
 *
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License (Version 2) as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * ########################################################################
 */


#include "ieee754sp.h"

int ieee754sp_class(ieee754sp x)
{
    COMPXSP;
    EXPLODEXSP;
    return xc;
}

int ieee754sp_isnan(ieee754sp x)
{
    return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
}

int ieee754sp_issnan(ieee754sp x)
{
    assert(ieee754sp_isnan(x));
    return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
}


ieee754sp ieee754sp_xcpt(ieee754sp r, const char *op, ...)
{
    struct ieee754xctx ax;

    if (!TSTX())
        return r;

    ax.op = op;
    ax.rt = IEEE754_RT_SP;
    ax.rv.sp = r;
    va_start(ax.ap, op);
    ieee754_xcpt(&ax);
    va_end(ax.ap);
    return ax.rv.sp;
}

ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
{
    struct ieee754xctx ax;

    assert(ieee754sp_isnan(r));

    if (!ieee754sp_issnan(r))   /* QNAN does not cause invalid op !! */
        return r;

    if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
        /* not enabled convert to a quiet NaN */
        SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
        if (ieee754sp_isnan(r))
            return r;
        else
            return ieee754sp_indef();
    }

    ax.op = op;
    ax.rt = 0;
    ax.rv.sp = r;
    va_start(ax.ap, op);
    ieee754_xcpt(&ax);
    va_end(ax.ap);
    return ax.rv.sp;
}

ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
{
    assert(ieee754sp_isnan(x));
    assert(ieee754sp_isnan(y));

    if (SPMANT(x) > SPMANT(y))
        return x;
    else
        return y;
}


static unsigned get_rounding(int sn, unsigned xm)
{
    /* inexact must round of 3 bits
     */
    if (xm & (SP_MBIT(3) - 1)) {
        switch (ieee754_csr.rm) {
        case IEEE754_RZ:
            break;
        case IEEE754_RN:
            xm += 0x3 + ((xm >> 3) & 1);
            /* xm += (xm&0x8)?0x4:0x3 */
            break;
        case IEEE754_RU:    /* toward +Infinity */
            if (!sn)    /* ?? */
                xm += 0x8;
            break;
        case IEEE754_RD:    /* toward -Infinity */
            if (sn) /* ?? */
                xm += 0x8;
            break;
        }
    }
    return xm;
}


/* generate a normal/denormal number with over,under handling
 * sn is sign
 * xe is an unbiased exponent
 * xm is 3bit extended precision value.
 */
ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
{
    assert(xm);     /* we don't gen exact zeros (probably should) */

    assert((xm >> (SP_MBITS + 1 + 3)) == 0);    /* no execess */
    assert(xm & (SP_HIDDEN_BIT << 3));

    if (xe < SP_EMIN) {
        /* strip lower bits */
        int es = SP_EMIN - xe;

        if (ieee754_csr.nod) {
            SETCX(IEEE754_UNDERFLOW);
            SETCX(IEEE754_INEXACT);

            switch(ieee754_csr.rm) {
            case IEEE754_RN:
            case IEEE754_RZ:
                return ieee754sp_zero(sn);
            case IEEE754_RU:      /* toward +Infinity */
                if(sn == 0)
                    return ieee754sp_min(0);
                else
                    return ieee754sp_zero(1);
            case IEEE754_RD:      /* toward -Infinity */
                if(sn == 0)
                    return ieee754sp_zero(0);
                else
                    return ieee754sp_min(1);
            }
        }

        if (xe == SP_EMIN - 1
                && get_rounding(sn, xm) >> (SP_MBITS + 1 + 3))
        {
            /* Not tiny after rounding */
            SETCX(IEEE754_INEXACT);
            xm = get_rounding(sn, xm);
            xm >>= 1;
            /* Clear grs bits */
            xm &= ~(SP_MBIT(3) - 1);
            xe++;
        }
        else {
            /* sticky right shift es bits
             */
            SPXSRSXn(es);
            assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
            assert(xe == SP_EMIN);
        }
    }
    if (xm & (SP_MBIT(3) - 1)) {
        SETCX(IEEE754_INEXACT);
        if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
            SETCX(IEEE754_UNDERFLOW);
        }

        /* inexact must round of 3 bits
         */
        xm = get_rounding(sn, xm);
        /* adjust exponent for rounding add overflowing
         */
        if (xm >> (SP_MBITS + 1 + 3)) {
            /* add causes mantissa overflow */
            xm >>= 1;
            xe++;
        }
    }
    /* strip grs bits */
    xm >>= 3;

    assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
    assert(xe >= SP_EMIN);

    if (xe > SP_EMAX) {
        SETCX(IEEE754_OVERFLOW);
        SETCX(IEEE754_INEXACT);
        /* -O can be table indexed by (rm,sn) */
        switch (ieee754_csr.rm) {
        case IEEE754_RN:
            return ieee754sp_inf(sn);
        case IEEE754_RZ:
            return ieee754sp_max(sn);
        case IEEE754_RU:    /* toward +Infinity */
            if (sn == 0)
                return ieee754sp_inf(0);
            else
                return ieee754sp_max(1);
        case IEEE754_RD:    /* toward -Infinity */
            if (sn == 0)
                return ieee754sp_max(0);
            else
                return ieee754sp_inf(1);
        }
    }
    /* gen norm/denorm/zero */

    if ((xm & SP_HIDDEN_BIT) == 0) {
        /* we underflow (tiny/zero) */
        assert(xe == SP_EMIN);
        if (ieee754_csr.mx & IEEE754_UNDERFLOW)
            SETCX(IEEE754_UNDERFLOW);
        return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
    } else {
        assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
        assert(xm & SP_HIDDEN_BIT);

        return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
    }
}