// BSD Unix TCP/IP Checksum


#!/usr/bin/env python

__author__="Andrew Pennebaker (andrew.pennebaker@gmail.com)"
__date__="21 Dec 2005 - 3 May 2006"
__copyright__="Copyright 2006 Andrew Pennebaker"
__version__="0.3"
__URL__="http://snippets.dzone.com/posts/show/3542"

import HashFunction

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

	INIT=0x00
	SUM_REQ="Sum >= 0"

	TEST_DATA="abc"
	TEST_HASH=0x40ac

	def __init__(self, sum=0x00):
		self.sum=sum

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

	def rotate(self, b):
		if (b&1)!=0:
			return (b>>1)+0x8000

		return b>>1

	def _update(self, b):
		self.sum=(self.rotate(self.sum)+b)&0xffff

	def digest(self):
		return self.sum

	def format(self, data):
		return "%05d" % (data)

	def unformat(self, hash):
		return int(hash)

if __name__=="__main__":
	HashFunction.main(BSD)