__author__="Andrew Pennebaker (andrew.pennebaker@gmail.com)"
__date__="21 Dec 2005 - 17 Jul 2006"
__copyright__="Copyright 2006 Andrew Pennebaker"
__license__="GPL"
__version__="0.3"
__URL__="http://snippets.dzone.com/posts/show/2889"

import HashFunction

class Adler32(HashFunction.HashFunction):
	BLOCK_SIZE=1
	DIGEST_SIZE=2

	INIT=0x0001
	SUM_REQ="Sum >= 0"

	BASE=65521

	TEST_DATA="abc"
	TEST_HASH=0x24d0127

	def __init__(self, sum=0x0001):
		self.sum=sum

	def sumValid(self, sum):
		return sum>=0

	def _update(self, b):
		s1=self.sum&0xffff
		s2=(self.sum>>16)&0xffff

		s1=(s1+(b&0xff))%self.BASE
		s2=(s1+s2)%self.BASE

		self.sum=(s2<<16)|s1

	def digest(self):
		return self.sum

	def formatDigest(self):
		return "%02x" % (self.digest())

	def unformatDigest(self, hash):
		return int(hash, 16)

if __name__=="__main__":
	HashFunction.main(Adler32, "Adler32.py")