This library, gmp_ecm, provides Ruby bindings to GMP-ECM, a C implementation of the Elliptic Curve Method for factorizing integers.

If you're using Bundler, add gem 'gmp_ecm' to your Gemfile.

If you just want to install with Rubygems, just gem install gmp_ecm.

The only dependency is the gmp gem, which provides Ruby bindings to GMP. The gmp gem is required because gmp_ecm passes around most numbers (input integer, resultant factors, and various parameters) as GMP::Z numbers.

gmp_ecm essentially just provides the GMP::Z#ecm_factor method (binding to GMP-ECM's ecm_params C function). So in order to start factorizing an integer, one must first initialize a GMP::Z integer, and then call #ecm_factor. Just as in the C library, this method requires the B1 parameter as the first parameter. Optionally, you can pass in a second parameter, the params, as either a Hash or an ECMParams object.

Not all of the fields in ecm_params are available yet. The current list of supported parameters is in the docs.

Here is an example of repeatedly hitting up GMP-ECM for factors of 2**71 - 1:

z = GMP::Z(2)**71 - 1 #=> 2361183241434822606847
z.ecm_factor(1_000_000)  #=> [1, 2361183241434822606847]
z.ecm_factor(1_000_000)  #=> [1, 11091312221959]
z.ecm_factor(1_000_000)  #=> [1, 2361183241434822606847]
z.ecm_factor(1_000_000)  #=> [1, 2361183241434822606847]
z.ecm_factor(1_000_000)  #=> [1, 48639942238007]

GMP::Z#ecm_factor returns a pair. The first element tells whether or not a factor was found:

• 1 means a factor was found in step 1.
• 2 means a factor was found in step 2.
• 0 means no factor was found.
• a negative value means an error occurred.

The ECMParams class is not implemented yet. For now, you can supply the ecm_params parameter as a hash:

• Any value expected to be a mpz_t can be a Fixnum or a GMP::Z.
• Any value expected to be an int, including unsigned, must be a Fixnum.
• Any value expected to be a double must be a ruby Float.
• Any value expected to be a FILE* must be a ruby IO object, typically created with File.open('filename', 'w').

gmp_ecm has been tested with, and should be compatible with:

• ruby 1.9.3, 2.0.0, 2.1.0-preview2
• GMP 5.0.5, 5.1.3
• GMP-ECM 6.3, 6.4.4
• Mac OS X 10.6

gmp_ecm is licensed under the Apache License, Version 2.0