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# mlpolygen - Maximal Length polynomial generator

MLPolyGen is a command line tool for generating maximal length (ML) polynomials for a linear feedback shift register (LFSR). MLPolyGen can generate ML polynomials of a specified order, or test whether a specified polynomial is maximal length. MLPolyGen can use the GNU Multiple Precision Arithmetic Library (GMP) to work with very large numbers. The larger the numbers, the more time it will take to compute.

## Building and Installing

This program is built with CMake, the cross-platform, open-source build system.
Typically the program is not built directly inside the source directory.
My preference is to build the program in a directory named `build`, located
in the root of the source directory.

To follow this approach:

$ cd mlpolygen-1.x.x # where you put the source code $ mkdir -p build $ cd build $ cmake .. $ make $ sudo make install

Normally, MLPolyGen requires GMP to build so that it can support numbers larger than 64 bits. If GMP is present on your system, CMake will automatically detect and use it. If you would like to disable the dependency on GMP, run CMake using the WITHOUT_GMP option as follows:

$ cmake -DWITHOUT_GMP=1 ..

## Usage examples

This section contains some examples for some common use cases. All of the options that are built in can shown by requesting help:

$ mlpolygen -?

To generate all of the maximal length polynomials of a particular order (e.g. 16):

$ mlpolygen 16 8016 801c ... fff5 fff6

These can also be generated using the symmetric pairs method. This is about twice as fast as the linear method (because it only has to search half the space), but it generates an unsorted output:

$ mlpolygen -p 16 8016 b400 ... fdbf fedf

To generate only few polynomials of a particular order:

$ mlpolygen -n4 16 8016 801c 801f 8029

To generate ML polynomials from a particular starting point:

$ mlpolygen -s 0xff00 ff12 ff18 ff24 ff41 ...

To generate a few *random* ML polynomials of a particular order:

$ mlpolygen -r -n4 16 b354 b5ab cca0 8299

To test whether specified polynomials are maximal length:

$ mlpolygen -t 0xb354 -t 0xb355 0xb354 is maximal length for order 16 0xb355 is NOT maximal length for order 16

## Testing

MLPolyGen includes code for testing its results. The testing is currently implemented using a simple makefile along with the stardard tools provided on a Unix system. To run the test, build according to the above instructions and then:

$ cd mlpolygen-1.x.x # where you put the source code $ cd test $ make

Refer to `test/Makefile` to see the tests performed, or increase the
order for which the tests are performed. Note that larger orders could
take hours (days, weeks) to complete.

## To do

- add a CLI switch to specify a stop polynomial value (so it could compute subsections in parallel)
- make sure it works on multiple platforms
- do some profiling to see if we can speed it up
- improve PrimeFactorizer to choose better prime candidates
- increase my CMake knowledge (I'm a noob)
- use CMake for testing (instead of the current Makefile)

## Acknowledgements and Background

- Thank you to Philip Koopman for providing his page on ML LFSR polynomials: http://www.ece.cmu.edu/~koopman/lfsr/index.html

- I've used his ML polynomials as reference material for a number of years
- The mlpolygen tester uses his polynomials for verification
- His page pointed me to
lfsr_s.c- Thank you to the author of
lfsr_s.c; I believe it was authored by Scott Nelson

lfsr_s.cwas once located atftp://helsbreth.org/pub/helsbret/random/lfsr_s.c- It contained no license when I downloaded it, and I can no longer find it on the internet
- I've included an unmodified copy of
lfsr_s.cinmlpolygen/src- mlpolygen is based on the algorithm described in
lfsr_s.c- I wrote mlpolygen while examining
lfsr_s.c, so portions of mlpolygen may be very loosely based onlfsr_s.c