In Files

  • prime.rb

Parent

Methods

Included Modules

Prime::EratosthenesSieve

Internal use. An implementation of eratosthenes's sieve

Public Instance Methods

next_to(n) click to toggle source

returns the least odd prime number which is greater than n.

 
               # File prime.rb, line 441
def next_to(n)
  n = (n-1).div(2)*2+3 # the next odd number to given n
  table_index, integer_index, bit_index = indices(n)
  loop do
    extend_table until @tables.length > table_index
    for j in integer_index...ENTRIES_PER_TABLE
      if !@tables[table_index][j].zero?
        for k in bit_index...BITS_PER_ENTRY
          return NUMS_PER_TABLE*table_index + NUMS_PER_ENTRY*j + 2*k+1 if !@tables[table_index][j][k].zero?
        end
      end
      bit_index = 0
    end
    table_index += 1; integer_index = 0
  end
end