Class
Internal use. An implementation of prime table by trial division method.
Instance Methods
lib/prime.rb
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# File tmp/rubies/ruby-2.4.10/lib/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 = @primes.at(@ulticheck_index + 1) ** 2
end
# 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
end
@primes[index]
end
Returns the +index+th prime number.
index
is a 0-based index.
#
lib/prime.rb
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# File tmp/rubies/ruby-2.4.10/lib/prime.rb, line 392
def cache
@primes
end
Returns the cached prime numbers.