usr/src/lib/libc/quad/floatdisf.c

/*-
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This software was developed by the Computer Systems Engineering group
 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
 * contributed to Berkeley.
 *
 * %sccs.include.redist.c%
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)floatdisf.c 8.1 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include "quad.h"

/*
 * Convert (signed) quad to float.
 */
float
__floatdisf(x)
        quad_t x;
{
        float f;
        union uu u;
        int neg;

        /*
         * Get an unsigned number first, by negating if necessary.
         */
        if (x < 0)
                u.q = -x, neg = 1;
        else
                u.q = x, neg = 0;

        /*
         * Now u.ul[H] has the factor of 2^32 (or whatever) and u.ul[L]
         * has the units.  Ideally we could just set f, add LONG_BITS to
         * its exponent, and then add the units, but this is portable
         * code and does not know how to get at an exponent.  Machine-
         * specific code may be able to do this more efficiently.
         *
         * Using double here may be excessive paranoia.
         */
        f = (double)u.ul[H] * ((1 << (LONG_BITS - 2)) * 4.0);
        f += u.ul[L];

        return (neg ? -f : f);
}