/* mkgmtime.c - make time corresponding to a GMT timeval struct
 *
 * Copyright (c) 1994-2008 Carnegie Mellon University.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Carnegie Mellon University
 *      Center for Technology Transfer and Enterprise Creation
 *      4615 Forbes Avenue
 *      Suite 302
 *      Pittsburgh, PA  15213
 *      (412) 268-7393, fax: (412) 268-7395
 *      innovation@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
/*
 * Copyright (c) 1987, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Arthur David Olson of the National Cancer Institute.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
** Adapted from code provided by Robert Elz, who writes:
**      The "best" way to do mktime I think is based on an idea of Bob
**      Kridle's (so its said...) from a long time ago. (mtxinu!kridle now).
**      It does a binary search of the time_t space.  Since time_t's are
**      just 32 bits, its a max of 32 iterations (even at 64 bits it
**      would still be very reasonable).
*/
/*
 * Fortunately, modern libc implementations on Linux, BSD and Solaris
 * provide a timegm() function that does exactly this but more efficiently
 * using the internal libc data structures.  We use that if configure
 * discovered it - gnb@fastmail.fm
 */

#include <config.h>

#if HAVE_TIMEGM

EXPORTED time_t mkgmtime(struct tm * const tmp)
{
    return timegm(tmp);
}

#else

#ifndef WRONG
#define WRONG   (-1)
#endif /* !defined WRONG */

static int
tmcomp(atmp, btmp)
register const struct tm * const atmp;
register const struct tm * const btmp;
{
        register int    result;

        if ((result = (atmp->tm_year - btmp->tm_year)) == 0 &&
                (result = (atmp->tm_mon - btmp->tm_mon)) == 0 &&
                (result = (atmp->tm_mday - btmp->tm_mday)) == 0 &&
                (result = (atmp->tm_hour - btmp->tm_hour)) == 0 &&
                (result = (atmp->tm_min - btmp->tm_min)) == 0)
                        result = atmp->tm_sec - btmp->tm_sec;
        return result;
}

time_t
mkgmtime(tmp)
struct tm * const       tmp;
{
        register int                    dir;
        register int                    bits;
        register int                    saved_seconds;
        time_t                          t;
        struct tm                       yourtm, *mytm;

        yourtm = *tmp;
        saved_seconds = yourtm.tm_sec;
        yourtm.tm_sec = 0;
        /*
        ** Calculate the number of magnitude bits in a time_t
        ** (this works regardless of whether time_t is
        ** signed or unsigned, though lint complains if unsigned).
        */
        for (bits = 0, t = 1; t > 0; ++bits, t <<= 1)
                ;
        /*
        ** If time_t is signed, then 0 is the median value,
        ** if time_t is unsigned, then 1 << bits is median.
        */
        t = (t < 0) ? 0 : ((time_t) 1 << bits);

        /* Some gmtime() implementations are broken and will return
         * NULL for time_ts larger than 40 bits even on 64-bit platforms
         * so we'll just cap it at 40 bits */
        if(bits > 40) bits = 40;

        for ( ; ; ) {
                mytm = gmtime(&t);

                if(!mytm) return WRONG;

                dir = tmcomp(mytm, &yourtm);
                if (dir != 0) {
                        if (bits-- < 0)
                                return WRONG;
                        if (bits < 0)
                                --t;
                        else if (dir > 0)
                                t -= (time_t) 1 << bits;
                        else    t += (time_t) 1 << bits;
                        continue;
                }
                break;
        }
        t += saved_seconds;
        return t;
}

#endif /* HAVE_TIMEGM */
