#!/usr/bin/env python
### log2_factorial -- Use Stirling's formula to estimate log2( n! ).
#                     See my factorial.py.  sw_at_not_this_tiac_dot_net
#
# For 0 <= n <= 170, this uses the actual factorial and is accurate to within
#                    the accuracy of the log() function.
# For 171 <= n <= 1e7, I've tested it and the answer seems accurate to within
#                    +1e-3.    That's a number of bits, so, pretty good.

from factorial import *
from sys import argv

if argv[1] == "-d":
   print defact( int( argv[2] ) )
elif argv[1] == "-b":
   print log2_factorial( int( argv[ 2 ] ) ) / 8, "bytes"
elif argv[1] == "-f":
   print factorial( int( argv[ 2 ] ) )
elif argv[1] == "-p":
   print pow( 2, float( argv[ 2 ] ) )
else:
   print log2_factorial( int( argv[ 1 ] ) )