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#MonthOfCode day 17 - random
import time
current_milli_time = lambda: int(round(time.time() * 1000))
# we use the Factory Design Pattern, RngCreator is the abstract class
class RngCreator(object):
def createRng(self):
raise NotImplementedError("Please Implement this method")
def inputParams(self, p_dict):
raise NotImplementedError("Please Implement this method")
class LcgCreator(RngCreator):
#default values
prod_a, prod_c, prod_m = 22695477,1, 2**32 #parameters used by the Borland C/C++ compiler
def createRng(self):
return Lcg(self.prod_a, self.prod_c, self.prod_m)
def inputParams(self, p_dict):
self.prod_a, self.prod_c, self.prod_m = p_dict['a'], p_dict['c'],p_dict['m']
class Lcg:
'''A linear congruential generator (LCG) is an algorithm that yields
a sequence of randomized numbers calculated with a linear equation.'''
seed = current_milli_time()
prev_val = seed
def __init__(self, a, c, m):
self.a, self.c, self.m = a,c,m
def randomRaw( self):
self.prev_val = (
self.a * self.prev_val + self.c) % self.m #formula for generating a new pseudo-rand number
return self.prev_val
def randint( self, binf, bsup):
if( bsup<= binf):
raise ValueError("bsup must be greater than binf")
random_var = self.randomRaw()
return binf +( random_var % (bsup-binf+1) )
def performTestRng( generator ):
''' simulates numerous dice throws! '''
NB_THROWS = 6* 100
occurences = [ 0 for i in xrange(6) ]
for n in xrange( NB_THROWS ):
nb = generator.randint(1,6)
print nb,
for i in range(1,7):
if(i == nb):
occurences[i-1]+=1
print ;
for i in range(1,7):
print "nb",i,"occurs",occurences[i-1]," ;",
print ;
generator1 = LcgCreator().createRng()
print "testing the first RNG:" ; performTestRng( generator1)
custom_creator = LcgCreator()
custom_creator.inputParams(
{'a':25214903917, 'c':11, 'm':2**48 } ) # parameters used by Java.util.Random
generator2 =custom_creator.createRng()
print "testing the second RNG:" ; performTestRng( generator2)

Instructive!

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