/*	SCCS Id: @(#)hacklib.c	3.4	2002/12/13	*/
/* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
/* Copyright (c) Robert Patrick Rankin, 1991		  */
/* NetHack may be freely redistributed.  See license for details. */
/* This was part of NetHack 3.4.3 hacklib.c */

#include <stdio.h>
#include <time.h>

static struct tm *
getlt()
{
        time_t date;
        (void) time(&date);
        return(localtime(&date));
}
/*
 * moon period = 29.53058 days ~= 30, year = 365.2422 days
 * days moon phase advances on first day of year compared to preceding year
 *  = 365.2422 - 12*29.53058 ~= 11
 * years in Metonic cycle (time until same phases fall on the same days of
 *  the month) = 18.6 ~= 19
 * moon phase on first day of year (epact) ~= (11*(year%19) + 29) % 30
 *  (29 as initial condition)
 * current phase in days = first day phase + days elapsed in year
 * 6 moons ~= 177 days
 * 177 ~= 8 reported phases * 22
 * + 11/22 for rounding
 */
int
phase_of_the_moon()     /* 0-7, with 0: new, 4: full */
{
    register struct tm *lt = getlt();
    register int epact, diy, goldn;

    diy = lt->tm_yday;
    goldn = (lt->tm_year % 19) + 1;
    epact = (11 * goldn + 18) % 30;
    if ((epact == 25 && goldn > 11) || epact == 24)
        epact++;

    return( (((((diy + epact) * 6) + 11) % 177) / 22) & 7 );
}

int main(int argc, char * argv[]) {
    printf ("phase of the moon %d\n\n", phase_of_the_moon());
}