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#!/usr/bin/python

#
# d2checksum.py - (c) 2010 mauvehead
#
# The file is a simple PoC for calculating the checksum of a Diablo II saved game file
#
# Because python does not have MAXINT in the way C does, additional bitwise operations
# are needed to ensure only the required bits are being kept from each bitshift
#
# Options:
#     -h, --help            show this help message and exit
#     -b, --bytes           print the contents of the file byte by byte
#     -d, --debug           displays additional output on the checksum processing
#     -s, --slow            decreases output refresh to 1 second intervals, used
#                           with --debug
#     -x, --expand          expand the checksum output to show every cycle of
#                           processing, used with --debug
#     -f FILE, --filename=FILE
#                           path to the character file
#


import os
import sys
import time
from optparse import OptionParser

prog = sys.argv[0]

def usage():
     usage = "usage: %s [-h] [options] -f filename" % prog
     return usage


def getArgs():
     parser = OptionParser(usage=usage())

     if len(sys.argv) <= 1:
          parser.error("you must specify at least a filename with -f, see --help for more details")

     parser.add_option("-b", "--bytes", action="store_const", const="1", dest="bytes",
                       help="print the contents of the file byte by byte")
     parser.add_option("-d", "--debug", action="store_const", const="1", dest="debug",
                       help="displays additional output on the checksum processing")
     parser.add_option("-s", "--slow", action="store_const", const="1", dest="slow",
                       help="decreases output refresh to 1 second intervals, used with --debug")
     parser.add_option("-x", "--expand", action="store_const", const="1", dest="expand",
                       help="expand the checksum output to show every cycle of processing, used with --debug")
     parser.add_option("-f", "--filename", action="store", dest="filename", default="NONE",
                       help="path to the character file")
     
     (options, args) = parser.parse_args()

     if options.filename == "NONE":
          parser.error("you must specify at least a filename with -f, see --help for more details")

     return options


def printBinary(num):
     binary = ''
     i = 31
     for i in range(31,-1,-1):
          if(num & (1 << i)):
               binary += "1"
          else:
               binary += "0"
     return binary


def calculateChecksum(options, filedata, filesize):
     checksum = i =  0

     if len(filedata) >= 15:
          for index in range(12,16,1):
               filedata[index] = 0

     for byte in filedata:
          if options.debug == '1':
               print "\n\n1) number preshift: %d"  % checksum
               print "1) checksum preshift: %s"  % printBinary(checksum)

          checksum = (checksum << 1) & 0xfffffffe | (checksum >> 31)

          if(options.debug == '1'):
               print "\n2) number postshift: %d"  % checksum
               print "2) checksum postshift: %s"  % printBinary(checksum)

          checksum = (checksum + byte) & 0xffffffff

	  if options.debug == '1':
               print "\n3) now add byte[%d]: 0x%X" % (i, byte)
               print "3) which is dec: %d"  % byte
               print "\n4) number post fileadd: %d"  % checksum
               print "4) checksum post fileadd: %s\n"  % printBinary(checksum)
               if(options.slow == '1'):
	            time.sleep(1)
               if((options.expand != '1') and (i < (filesize - 1))):
	            os.system("clear")
               i += 1
     if options.debug == '1':
          print "5) number after loop: %d"  % checksum
          print "5) checksum after loop: %s"  % printBinary(checksum)
	  print ""
     return checksum


def readFile(filename, filesize):
     filedata = []
     f = open(filename,'rb')
     try:
	  header = f.read(4)
	  if header.encode("hex") != "55aa55aa":
               print "%s: error: header on %s does not match known DiabloII header: invalid file" % (prog,filename)
	       sys.exit(1)
	  f.seek(0)
          ch = f.read(1)
          while ch:
               filedata.append(ord(ch))
               ch = f.read(1)
     finally:
          f.close()
     return filedata


def printBytes(filedata):
     i = 0

     for byte in filedata:
          print "byte[%d]: %x" % (i, byte)
	  i += 1
     sys.exit(0)


def getFilesize(filename):
     if os.path.isfile(filename):
          filesize = os.path.getsize(filename)
     else:
          print "%s: error: unable to open file: %s" % (prog,filename)
	  sys.exit(1)
     return filesize


def main():
     options = getArgs()
     filesize = getFilesize(options.filename)
     filedata = readFile(options.filename, filesize)

     if options.bytes == '1':
          printBytes(filedata)
     
     checksum = calculateChecksum(options, filedata, filesize)

     print "Checksum hex: 0x%X" % checksum
     return 0


# RUN MAIN()
if __name__ == "__main__":
     main()