rubyで即値になる数値とobjectになる数値の境界を探す

fixnum_immediate_value_boundary.rb

def immediate_value?(number)
  (number.object_id >> 1) == number
end

def bin_search(min, max)
  # p [:try, min, max]
  if (max - min) <= 1
    puts "stop"
    puts "min: #{min}, bit_length: #{min.bit_length} check: #{immediate_value?(min)}"
    puts "max: #{max}, bit_length: #{max.bit_length} check: #{immediate_value?(max)}"
  else
    center = (max + min) / 2
    if immediate_value?(center)
      bin_search(center, max)
    else
      bin_search(min, center)
    end
  end
end

bin_search(1, 2 ** 64 - 1)

https://github.com/ruby/ruby/blob/1bd60c66d385142d08f678f8a9563c311cfc3fe8/include/ruby/ruby.h#L257
を元にチェック

show_fix_num_max.c

#include <stdio.h>
#include <limits.h>

int main(void) {
  printf("LONG_MAX >> 1 = %ld\n", LONG_MAX >> 1);

  return 0;
}

% gcc show_fix_num_max.c
% ./a.out
LONG_MAX >> 1 = 4611686018427387903
% ruby fixnum_immediate_value_boundary.rb
stop
min: 4611686018427387903, bit_length: 62 check: true
max: 4611686018427387904, bit_length: 63 check: false