Testing BigDecimal in Ruby

bigdecimal-test.rb

require 'bigdecimal'

def _sprintf num
  ('%0.45f' % num).sub(/0+$/,'')
end

n = 1
loop do
  n += 1

  b = 2 ** n
  a = b - 1

  x = BigDecimal(a)
  y = BigDecimal(b)
  d = x / y
  r = Rational(a, b)

  next if r == d.to_r

  puts "((2 ** #{n}) - 1) / (2 ** #{n})"
  puts " #{x} / #{y}"
  puts "  BigDecimal:"
  puts "    \#to_s     #{d.to_s}"
  puts "    sprintf   #{_sprintf d}"
  puts "    \#to_r     #{d.to_r.inspect}"
  puts "  Rational:"
  puts "    sprintf   #{_sprintf r}"
  puts "    \#to_r     #{r.inspect}"

  d2 = BigDecimal(_sprintf d)
  r2 = Rational(_sprintf d)
  puts 'construct from (sprintf % BigDecimal)'
  puts "  BigDecimal: #{d2.to_s}"
  puts "              #{d2.to_r.inspect}"
  puts "  Rational:   #{r2.inspect}"

  d3 = BigDecimal(d.to_s)
  r3 = Rational(d.to_s)
  puts 'construct from (BigDecimal#to_s)'
  puts "  BigDecimal: #{d3.to_s}"
  puts "              #{d3.to_r.inspect}"
  puts "  Rational:   #{r3.inspect}"

  puts ''

  break if r != d
end

jruby-2.3.1-output.txt

$ jruby/bin/jruby -v bigdecimal.rb 
jruby 9.1.3.0-SNAPSHOT (2.3.1) 2016-08-20 6600d9f OpenJDK 64-Bit Server VM 25.131-b11 on 1.8.0_131-8u131-b11-0ubuntu1.16.04.2-b11 +jit [linux-x86_64]
((2 ** 19) - 1) / (2 ** 19)
 0.524287E6 / 0.524288E6
  BigDecimal:
    #to_s     0.9999980926513671875E0
    sprintf   0.9999980926513672
    #to_r     (9999980926513671875/9223372036854775807)
  Rational:
    sprintf   0.9999980926513672
    #to_r     (524287/524288)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999980926513672E0
              (1249997615814209/1250000000000000)
  Rational:   (1249997615814209/1250000000000000)
construct from (BigDecimal#to_s)
  BigDecimal: 0.9999980926513671875E0
              (9999980926513671875/9223372036854775807)
  Rational:   (524287/524288)

$ 

ruby-2.4.0-output.txt

$ ruby -v bigdecimal.rb 
ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]
((2 ** 19) - 1) / (2 ** 19)
 0.524287e6 / 0.524288e6
  BigDecimal:
    #to_s     0.999998092651367188e0
    sprintf   0.9999980926513671875
    #to_r     (249999523162841797/250000000000000000)
  Rational:
    sprintf   0.9999980926513671875
    #to_r     (524287/524288)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999980926513671875e0
              (524287/524288)
  Rational:   (524287/524288)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999998092651367188e0
              (249999523162841797/250000000000000000)
  Rational:   (249999523162841797/250000000000000000)

((2 ** 20) - 1) / (2 ** 20)
 0.1048575e7 / 0.1048576e7
  BigDecimal:
    #to_s     0.999999046325683594e0
    sprintf   0.99999904632568359375
    #to_r     (499999523162841797/500000000000000000)
  Rational:
    sprintf   0.99999904632568359375
    #to_r     (1048575/1048576)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.99999904632568359375e0
              (1048575/1048576)
  Rational:   (1048575/1048576)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999046325683594e0
              (499999523162841797/500000000000000000)
  Rational:   (499999523162841797/500000000000000000)

((2 ** 21) - 1) / (2 ** 21)
 0.2097151e7 / 0.2097152e7
  BigDecimal:
    #to_s     0.999999523162841797e0
    sprintf   0.999999523162841796875
    #to_r     (999999523162841797/1000000000000000000)
  Rational:
    sprintf   0.999999523162841796875
    #to_r     (2097151/2097152)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.999999523162841796875e0
              (2097151/2097152)
  Rational:   (2097151/2097152)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999523162841797e0
              (999999523162841797/1000000000000000000)
  Rational:   (999999523162841797/1000000000000000000)

((2 ** 22) - 1) / (2 ** 22)
 0.4194303e7 / 0.4194304e7
  BigDecimal:
    #to_s     0.999999761581420898e0
    sprintf   0.9999997615814208984375
    #to_r     (499999880790710449/500000000000000000)
  Rational:
    sprintf   0.9999997615814208984375
    #to_r     (4194303/4194304)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999997615814208984375e0
              (4194303/4194304)
  Rational:   (4194303/4194304)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999761581420898e0
              (499999880790710449/500000000000000000)
  Rational:   (499999880790710449/500000000000000000)

((2 ** 23) - 1) / (2 ** 23)
 0.8388607e7 / 0.8388608e7
  BigDecimal:
    #to_s     0.999999880790710449e0
    sprintf   0.99999988079071044921875
    #to_r     (999999880790710449/1000000000000000000)
  Rational:
    sprintf   0.99999988079071044921875
    #to_r     (8388607/8388608)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.99999988079071044921875e0
              (8388607/8388608)
  Rational:   (8388607/8388608)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999880790710449e0
              (999999880790710449/1000000000000000000)
  Rational:   (999999880790710449/1000000000000000000)

((2 ** 24) - 1) / (2 ** 24)
 0.16777215e8 / 0.16777216e8
  BigDecimal:
    #to_s     0.999999940395355225e0
    sprintf   0.999999940395355224609375
    #to_r     (39999997615814209/40000000000000000)
  Rational:
    sprintf   0.999999940395355224609375
    #to_r     (16777215/16777216)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.999999940395355224609375e0
              (16777215/16777216)
  Rational:   (16777215/16777216)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999940395355225e0
              (39999997615814209/40000000000000000)
  Rational:   (39999997615814209/40000000000000000)

((2 ** 25) - 1) / (2 ** 25)
 0.33554431e8 / 0.33554432e8
  BigDecimal:
    #to_s     0.999999970197677612e0
    sprintf   0.9999999701976776123046875
    #to_r     (249999992549419403/250000000000000000)
  Rational:
    sprintf   0.9999999701976776123046875
    #to_r     (33554431/33554432)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999999701976776123046875e0
              (33554431/33554432)
  Rational:   (33554431/33554432)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999970197677612e0
              (249999992549419403/250000000000000000)
  Rational:   (249999992549419403/250000000000000000)

((2 ** 26) - 1) / (2 ** 26)
 0.67108863e8 / 0.67108864e8
  BigDecimal:
    #to_s     0.999999985098838806e0
    sprintf   0.99999998509883880615234375
    #to_r     (499999992549419403/500000000000000000)
  Rational:
    sprintf   0.99999998509883880615234375
    #to_r     (67108863/67108864)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.99999998509883880615234375e0
              (67108863/67108864)
  Rational:   (67108863/67108864)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999985098838806e0
              (499999992549419403/500000000000000000)
  Rational:   (499999992549419403/500000000000000000)

((2 ** 27) - 1) / (2 ** 27)
 0.134217727e9 / 0.134217728e9
  BigDecimal:
    #to_s     0.999999992549419403e0
    sprintf   0.999999992549419403076171875
    #to_r     (999999992549419403/1000000000000000000)
  Rational:
    sprintf   0.999999992549419403076171875
    #to_r     (134217727/134217728)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.999999992549419403076171875e0
              (134217727/134217728)
  Rational:   (134217727/134217728)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999992549419403e0
              (999999992549419403/1000000000000000000)
  Rational:   (999999992549419403/1000000000000000000)

((2 ** 28) - 1) / (2 ** 28)
 0.268435455e9 / 0.268435456e9
  BigDecimal:
    #to_s     0.999999996274709702e0
    sprintf   0.9999999962747097015380859375
    #to_r     (499999998137354851/500000000000000000)
  Rational:
    sprintf   0.9999999962747097015380859375
    #to_r     (268435455/268435456)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999999962747097015380859375e0
              (268435455/268435456)
  Rational:   (268435455/268435456)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999996274709702e0
              (499999998137354851/500000000000000000)
  Rational:   (499999998137354851/500000000000000000)

((2 ** 29) - 1) / (2 ** 29)
 0.536870911e9 / 0.536870912e9
  BigDecimal:
    #to_s     0.999999998137354851e0
    sprintf   0.99999999813735485076904296875
    #to_r     (999999998137354851/1000000000000000000)
  Rational:
    sprintf   0.99999999813735485076904296875
    #to_r     (536870911/536870912)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.99999999813735485076904296875e0
              (536870911/536870912)
  Rational:   (536870911/536870912)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999998137354851e0
              (999999998137354851/1000000000000000000)
  Rational:   (999999998137354851/1000000000000000000)

((2 ** 37) - 1) / (2 ** 37)
 0.137438953471e12 / 0.137438953472e12
  BigDecimal:
    #to_s     0.999999999992724042385816574096679687e0
    sprintf   0.9999999999927240423858165740966796875
    #to_r     (999999999992724042385816574096679687/1000000000000000000000000000000000000)
  Rational:
    sprintf   0.9999999999927240423858165740966796875
    #to_r     (137438953471/137438953472)
construct from (sprintf % BigDecimal)
  BigDecimal: 0.9999999999927240423858165740966796875e0
              (137438953471/137438953472)
  Rational:   (137438953471/137438953472)
construct from (BigDecimal#to_s)
  BigDecimal: 0.999999999992724042385816574096679687e0
              (999999999992724042385816574096679687/1000000000000000000000000000000000000)
  Rational:   (999999999992724042385816574096679687/1000000000000000000000000000000000000)

$