class PrimeSieve
Attributes
primes[R]
Frozen array of prime numbers up to the pre-calculation limit.
@return [Array<Integer>]
Public Class Methods
new(precalculation_limit = 10**7)
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Create a new PrimeSieve
.
@param precalculation_limit [#to_i] calculate primality lookup, and generate prime numbers up to this value @raise [Ulaminate::TypeError] if precalculation_limit is not a positive integer
# File lib/prime_sieve.rb, line 16 def initialize(precalculation_limit = 10**7) @precalculation_limit = precalculation_limit.to_i @precalculation_limit > 0 or raise Ulaminate::TypeError, "#{@precalculation_limit} must be positive" @is_prime = ~Bitset.new(@precalculation_limit + 1) @is_prime.clear(0, 1) @primes = [] 2.upto(@precalculation_limit) do |i| next unless @is_prime[i] (i**2..@precalculation_limit).step(i) do |j| @is_prime[j] = false end primes << i end @primes.freeze end
Public Instance Methods
prime?(number)
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Determines whether the given number is prime.
@param number [#to_i] @return [Boolean] whether number is prime @raise [Ulaminate::TypeError] if number is not a positive integer
# File lib/prime_sieve.rb, line 43 def prime?(number) n = number.to_i n > 0 or raise Ulaminate::TypeError, "#{n} must be positive" return @is_prime[n] if n <= @precalculation_limit primes.all? { |prime| n % prime != 0 } end