Ruby max integer

Hello, I need to be able to determine a systems maximum integer in Ruby. Anybody know how, or if it's possible?

From stackoverflow

• In ruby Fixnums are automatically converted to Bignums.

  To find the highest possible Fixnum you could do something like this:

  class Fixnum
   N_BYTES = [42].pack('i').size
   N_BITS = N_BYTES * 8
   MAX = 2 ** (N_BITS - 2) - 1
   MIN = -MAX - 1
  end
  p(Fixnum::MAX)
  

  Shamelessly ripped from a ruby-talk discussion. Look there for more details.

• Ruby automatically converts integers to a large integer class when they overflow, so there's (practically) no limit to how big they can be.

  If you are looking for the machine's size, i.e. 64- or 32-bit, I found this trick at ruby-forum.com (http://www.ruby-forum.com/topic/177435):

  machine_bytes = ['foo'].pack('p').size
  machine_bits = machine_bytes * 8
  machine_max_signed = 2**(machine_bits-1) - 1
  machine_max_unsigned = 2**machine_bits - 1
  

  Edit: If you are looking for the size of Fixnum objects (integers small enough to store in a single machine word), you can call 0.size to get the number of bytes. I would guess it should be 4 on 32-bit builds, but I can't test that right now. Also, the largest Fixnum is apparently 2**30 - 1 (or 2**62 - 1), because one bit is used to mark it as an integer instead of an object reference.

  Cebjyre : Pretty sure you want 2**(machine_size * 8) -1; 2**4-1=15 which is not a very large anything.

  Matthew Crumley : Whoops, I guess I started thinking too much about bytes instead of bits.

• Reading the friendly manual? Who'd want to do that?

  start = Time.now
  largest_known_fixnum = 1
  smallest_known_bignum = nil
  until (smallest_known_bignum and smallest_known_bignum == largest_known_fixnum + 1)
    if smallest_known_bignum.nil?
      next_number_to_try = largest_known_fixnum * 1000
    else
      next_number_to_try = (smallest_known_bignum + largest_known_fixnum) / 2 #Geometric mean would be more efficient, but more risky
    end
    raise "Can't happen case" if next_number_to_try <= largest_known_fixnum or (smallest_known_bignum and next_number_to_try >= smallest_known_bignum)
    if next_number_to_try.class == Bignum
      smallest_known_bignum = next_number_to_try
    elsif next_number_to_try.class == Fixnum
      largest_known_fixnum = next_number_to_try
    else
      raise "Can't happen case"
    end
  end
  finish = Time.now
  puts "The largest fixnum is #{largest_known_fixnum}"
  puts "The smallest bignum is #{smallest_known_bignum}"
  puts "Calculation took #{finish - start} seconds"
  

• FIXNUM_MAX = (2**(0.size * 8 -2) -1)
  FIXNUM_MIN = -(2**(0.size * 8 -2))