#!/usr/bin/env python
#
#       Collatz numbers, Hailstone algorithm
#
#       Copyright (c) 2014 Scheerer Software
#       Author: Franz Scheerer <scheerer.software@gmail.com>
#
#       This program is free software; you can redistribute it and/or modify
#       it under the terms of the GNU General Public License as published by
#       the Free Software Foundation; either version 2 of the License, or
#       (at your option) any later version.
#       
#       This program is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#       
#       You should have received a copy of the GNU General Public License
#       along with this program; if not, write to the Free Software
#       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#       MA 02110-1301, USA.
#

def Efile(nam, keytxt):
  keyn = 117
  for char in keytxt:
    keyn = 256 * keyn + ord(char)
  f = open(nam,'r')
  data = f.read()
  cipher = CollatzE(data, keyn)
  f.close()
  fnam = nam + '.enc'
  f = open(fnam, 'w' )
  f.write(cipher)
  f.close()

def Dfile(nam, keytxt):
  keyn = 117
  for char in keytxt:
    keyn = 256 * keyn + ord(char)
  fnam = nam + '.enc'
  f = open(fnam,'r')
  cipher = f.read()
  data = CollatzD(cipher, keyn)
  f.close()
  f = open(nam, 'w')
  f.write(data)
  f.close()

def CollatzE(data, key):
    up = 3**90
    low = 2**42 + 7
    out = []
    for char in data:
      byval = 0
      for bit in range(8):
        if key < low:
          while key < up:
            key = key**2 + 7
        if key % 2:
           key = (3*key+1)/2
        else:
           key = key/2
        byval = byval + ((key & 1) << bit)
      key = key + ord(char)
      out.append(chr( (ord(char) ^ byval) & 255) )
    return ''.join(out)

def CollatzD(data, key):
    up = 3**90
    low = 2**42 + 7
    out = []
    for char in data:
      byval = 0
      for bit in range(8):
        if key < low:
          while key < up:
            key = key**2 + 7
        if key % 2:
           key = (3*key+1)/2
        else:
           key = key/2
        byval = byval + ((key & 1) << bit)
      key = key + ((ord(char) ^ byval) & 255)
      out.append(chr( (ord(char) ^ byval) & 255) )
    return ''.join(out)