/*
 * (C)2012 Michael Duane Rice All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. 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. Neither the name of the copyright holders
 * nor the names of contributors may be used to endorse or promote products
 * derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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
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 */

/* $Id: gm_sidereal.c 2369 2013-04-28 14:19:35Z swfltek $ */

/*
    Greenwich Mean Sidereal Time. A sidereal second is somewhat shorter than a standard second,
    about 1.002737909350795 sidereal seconds per standard second.

    We resort to fixed point math due to the insufficient resolution of a 'double', using...

        timestamp * ( 1.002737909350795 << 31 )
        --------------------------------------- + Te
                        1 << 31

    Where Te is the sidereal time at the epoch.

*/

#include <time.h>
#include <stdint.h>

unsigned long
gm_sidereal(const time_t * timer)
{
    uint64_t        tmp;

    tmp = *timer;
    tmp *= 0x8059B740;
    tmp /= 0x80000000;
    tmp += (uint64_t) 23991;

    tmp %= ONE_DAY;
    return tmp;
}