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pyfsr Build Status

This module was developed in the course of a bachelor thesis and is in no way suitable for use in production. It enables a simple generation of pseudo random bit streams by providing linear and non-linear feedback shift register implementations.

Installation

This package is currently not released on PyPI and must therefore be installed locally. To do that you have the following two options:

install with pip + github url

# install
$ pip install -e git+git://github.com/luukbox/pyfsr@master#egg=pyfsr

# upgrade
$ pip install --upgrade -e git+git://github.com/luukbox/pyfsr@master#egg=pyfsr

clone the repository and build it in your working directory

$ pip install setuptools
$ git clone https://github.com/luukbox/pyfsr.git
$ cd pyfsr
$ python setup.py sdist
$ pip install ./dist/pyfsr-VERSION_GOES_HERE.tar.gz

Examples

LFSR

from pyfsr import LFSR, FSRFunction

# x^3 + x^2 + 1
l = LFSR(poly=[3,2], initstate=[0,1,0])
print(l.sequence(5))
# --> [0 1 0 1 1]

l = LFSR(poly=[3,2], initstate=[0,1,0], initcycles=3)
print(l.sequence(5))
# --> [1 1 1 0 0]

l = LFSR(poly=[3, 2], initstate=[0, 1, 0],
         initcycles=3, feedback='internal')
print(l.sequence(5))
# --> [1 0 1 0 0]

fsrfunc = FSRFunction([4, 3, '*', 0, '+'])
l = LFSR(poly=[5, 3], initstate=[0, 1, 0, 1, 1], outfunc=fsrfunc)
print(l.shift())
# --> 1 (l.state[4] and l.state[3] xor l.state[0])

print(l) # type_poly_feedback[_outfunc]
# --> lfsr_(5-3)_ext_out(4-3-and-0-xor)

NLFSR

Use a non linear input function. Otherwise the resulting FSR would be a less efficient LFSR.

from pyfsr import NLFSR, FSRFunction

infunc = FSRFunction([3, 2, 4, "*", "+"])
nl = NLFSR(initstate=[0, 1, 0, 0, 1], infunc=infunc)
print(nl.sequence(10))
# --> [1 0 0 1 0 0 0 1 0 0]

outfunc = FSRFunction([1, 2, 3, "+", "+"])
nl = NLFSR(initstate="ones", infunc=infunc,
           outfunc=outfunc, size=5, initcycles=13)
print(nl.sequence(10))
# --> [1 1 1 0 1 1 1 0 1 1]

print(nl) # type_size_infunc[_outfunc]
# --> nfsr_5_in(3-2-4-and-xor)_out(1-2-3-xor-xor)

FSRFunction

Functions in Reverse Polish notation. Operands are indices of the solve methods parameter (the FSR state).

Operators:

  • '+' (xor)
  • '*' (and)
fsrfunc = FSRFunction([4, 3, '+',  1, 2, '*', '+'])
print(fsrfunc.solve([0, 1, 0, 0, 1]))
# --> 1 [(0 xor 1) xor (0 and 1)]