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

/*-
 * Copyright (c) 1992 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[] = "@(#)fixunsdfdi.c        5.4 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include "quad.h"

#define ONE_FOURTH      (1 << (LONG_BITS - 2))
#define ONE_HALF        (ONE_FOURTH * 2.0)
#define ONE             (ONE_FOURTH * 4.0)

/*
 * Convert double to (unsigned) quad.
 * Not sure what to do with negative numbers---for now, anything out
 * of range becomes UQUAD_MAX.
 */
u_quad_t
__fixunsdfdi(x)
        double x;
{
        double toppart;
        union uu t;

        if (x < 0)
                return (UQUAD_MAX);     /* ??? should be 0?  ERANGE??? */
        if (x >= UQUAD_MAX)
                return (UQUAD_MAX);
        /*
         * Get the upper part of the result.  Note that the divide
         * may round up; we want to avoid this if possible, so we
         * subtract `1/2' first.
         */
        toppart = (x - ONE_HALF) / ONE;
        /*
         * Now build a u_quad_t out of the top part.  The difference
         * between x and this is the bottom part (this may introduce
         * a few fuzzy bits, but what the heck).  With any luck this
         * difference will be nonnegative: x should wind up in the
         * range [0..ULONG_MAX].  For paranoia, we assume [LONG_MIN..
         * 2*ULONG_MAX] instead.
         */
        t.ul[H] = (unsigned long)toppart;
        t.ul[L] = 0;
        x -= (double)t.uq;
        if (x < 0) {
                t.ul[H]--;
                x += ULONG_MAX;
        }
        if (x > ULONG_MAX) {
                t.ul[H]++;
                x -= ULONG_MAX;
        }
        t.ul[L] = (u_long)x;
        return (t.uq);
}