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POHow to port this NetHack function to Python?
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copied!<p>I am trying to write a Python function which returns the same moon phase value as in the game NetHack. This is found in <a href="http://nethack.wikia.com/wiki/Source:Hacklib.c#phase_of_the_moon" rel="nofollow noreferrer">hacklib.c</a>.</p> <p>I have tried to simply copy the corresponding function from the NetHack code but I don't believe I am getting the correct results.</p> <p>The function which I have written is <code>phase_of_the_moon()</code>.</p> <p>The functions <code>position()</code> and <code>phase()</code>, I found on the net, and I am using them as an indication of the success of my function. They are very accurate and give results which approximately match the nethack.alt.org server (see <a href="http://alt.org/nethack/moon/pom.txt" rel="nofollow noreferrer">http://alt.org/nethack/moon/pom.txt</a>). What I am after however is an exact replication of the original NetHack function, idiosyncrasies intact.</p> <p>I would expect my function and the 'control' function to give the same moon phase at least, but currently they do not and I'm not sure why!</p> <p>Here is the NetHack code:</p> <pre><code>/* * 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 ); } </code></pre> <p>Here is the <code>getlt()</code> function (also in hacklib.c):</p> <pre><code>static struct tm * getlt() { time_t date; #if defined(BSD) && !defined(POSIX_TYPES) (void) time((long *)(&date)); #else (void) time(&date); #endif #if (defined(ULTRIX) && !(defined(ULTRIX_PROTO) || defined(NHSTDC))) || (defined(BSD) && !defined(POSIX_TYPES)) return(localtime((long *)(&date))); #else return(localtime(&date)); #endif } </code></pre> <p>Here is my Python code:</p> <pre><code>from datetime import date def phase_of_the_moon(): lt = date.today() diy = (lt - date(lt.year, 1, 1)).days goldn = ((lt.year - 1900) % 19) + 1 epact = (11 * goldn + 18) % 30; if ((epact == 25 and goldn > 11) or epact == 24): epact += 1 return ( (((((diy + epact) * 6) + 11) % 177) / 22) & 7 ) import math, decimal, datetime dec = decimal.Decimal def position(now=None): if now is None: now = datetime.datetime.now() diff = now - datetime.datetime(2001, 1, 1) days = dec(diff.days) + (dec(diff.seconds) / dec(86400)) lunations = dec("0.20439731") + (days * dec("0.03386319269")) return lunations % dec(1) def phase(pos): index = (pos * dec(8)) + dec("0.5") index = math.floor(index) return { 0: "New Moon", 1: "Waxing Crescent", 2: "First Quarter", 3: "Waxing Gibbous", 4: "Full Moon", 5: "Waning Gibbous", 6: "Last Quarter", 7: "Waning Crescent" }[int(index) & 7] def phase2(pos): return { 0: "New Moon", 1: "Waxing Crescent", 2: "First Quarter", 3: "Waxing Gibbous", 4: "Full Moon", 5: "Waning Gibbous", 6: "Last Quarter", 7: "Waning Crescent" }[int(pos)] def main(): ## Correct output pos = position() phasename = phase(pos) roundedpos = round(float(pos), 3) print "%s (%s)" % (phasename, roundedpos) ## My output print "%s (%s)" % (phase2(phase_of_the_moon()), phase_of_the_moon()) if __name__=="__main__": main() </code></pre>

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