dp_modf.c

Go to the documentation of this file.

/* IEEE754 floating point arithmetic
 * double precision: common utilities
 */
/*
 * 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 "ieee754dp.h"

/* modf function is always exact for a finite number
*/
ieee754dp ieee754dp_modf(ieee754dp x, ieee754dp *ip)
{
    COMPXDP;

    CLEARCX;

    EXPLODEXDP;

    switch (xc) {
    case IEEE754_CLASS_SNAN:
    case IEEE754_CLASS_QNAN:
    case IEEE754_CLASS_INF:
    case IEEE754_CLASS_ZERO:
        *ip = x;
        return x;
    case IEEE754_CLASS_DNORM:
        /* far to small */
        *ip = ieee754dp_zero(xs);
        return x;
    case IEEE754_CLASS_NORM:
        break;
    }
    if (xe < 0) {
        *ip = ieee754dp_zero(xs);
        return x;
    }
    if (xe >= DP_MBITS) {
        *ip = x;
        return ieee754dp_zero(xs);
    }
    /* generate ipart mantissa by clearing bottom bits
     */
    *ip = builddp(xs, xe + DP_EBIAS,
              ((xm >> (DP_MBITS - xe)) << (DP_MBITS - xe)) &
              ~DP_HIDDEN_BIT);

    /* generate fpart mantissa by clearing top bits
     * and normalizing (must be able to normalize)
     */
    xm = (xm << (64 - (DP_MBITS - xe))) >> (64 - (DP_MBITS - xe));
    if (xm == 0)
        return ieee754dp_zero(xs);

    while ((xm >> DP_MBITS) == 0) {
        xm <<= 1;
        xe--;
    }
    return builddp(xs, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
}