MrdPrime

Miller-Rabin Prime Number Determination.

A small number(~2^81) makes a definitive decision. A large number will fallback to OpenSSL::BN::prime?.

In order to reduce the amount of calculation, a decision is made using the minimum amount of calculation. For example, just testing on 2 will determine up to 2047. Testing on 2 and 3, gives a decision up to 1373653.

https://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test#Testing_against_small_sets_of_bases
"if n < 3,317,044,064,679,887,385,961,981,
it is enough to test a = 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, and 41.
and the result will be deterministic."

Add this line to your application's Gemfile:

gem 'mrd_prime'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install mrd_prime

require 'mrd_prime'

small_number = (2**79 + 23)

puts( small_number.mrd_prime? )  #=> true

If you want to use the name prime?, you can alias it.

class Integer
	alias_method :prime?, :mrd_prime?
end

puts( (2**79 + 23).prime? )  #=> true

Bug reports and pull requests are welcome on GitHub at https://github.com/Matsuyanagi/mrd_prime .