In Files

  • prime.rb


Included Modules


Internal use. An implementation of prime table by trial division method.

Public Instance Methods

[](index) click to toggle source

Returns the +index+th prime number.

index is a 0-based index.

               # File prime.rb, line 401
def [](index)
  while index >= @primes.length
    # Only check for prime factors up to the square root of the potential primes,
    #   but without the performance hit of an actual square root calculation.
    if @next_to_check + 4 > @ulticheck_next_squared
      @ulticheck_index += 1
      @ulticheck_next_squared = + 1) ** 2
    # Only check numbers congruent to one and five, modulo six. All others

    #   are divisible by two or three.  This also allows us to skip checking against
    #   two and three.
    @primes.push @next_to_check if @primes[2..@ulticheck_index].find {|prime| @next_to_check % prime == 0 }.nil?
    @next_to_check += 4
    @primes.push @next_to_check if @primes[2..@ulticheck_index].find {|prime| @next_to_check % prime == 0 }.nil?
    @next_to_check += 2
  return @primes[index]
cache() click to toggle source

Returns the cached prime numbers.

               # File prime.rb, line 392
def cache
  return @primes
Also aliased as: primes, primes_so_far
primes() click to toggle source
Alias for: cache
primes_so_far() click to toggle source
Alias for: cache

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