Branch prediction is detectable on jruby

branch_predict.rb

require 'benchmark'

array_size = 32768
data = Array.new(array_size)

array_size.times { |c| data[c] = rand(256)}

data_sorted = data.sort

def sum(array)
    sum = 0;

    for i in 1..1000 # calm down, MRI is slooowwww
        for j in 0..(array.size - 1)
            sum += array[j] if array[j] >= 128
        end
    end

    puts "Total: #{sum}"
end

puts 'Unsorted'

5.times { puts Benchmark.measure { sum(data) } }

puts 'Sorted'

5.times { puts Benchmark.measure { sum(data_sorted) } }

result.txt

$ /usr/bin/ruby branch_predict.rb 
Unsorted
Total: 3159277000
 15.750000   0.020000  15.770000 ( 16.237136)
Total: 3159277000
 15.900000   0.030000  15.930000 ( 16.129206)
Total: 3159277000
 15.830000   0.010000  15.840000 ( 16.007797)
Total: 3159277000
 15.810000   0.030000  15.840000 ( 16.122798)
Total: 3159277000
 15.830000   0.020000  15.850000 ( 16.215970)
Sorted
Total: 3159277000
 15.810000   0.030000  15.840000 ( 16.722894)
Total: 3159277000
 15.790000   0.010000  15.800000 ( 15.894834)
Total: 3159277000
 15.750000   0.010000  15.760000 ( 15.970007)
Total: 3159277000
 15.800000   0.020000  15.820000 ( 16.326240)
Total: 3159277000
 15.660000   0.020000  15.680000 ( 15.868698)

$ jruby branch_predict.rb 
Unsorted
Total: 3154163000
  2.920000   0.130000   3.050000 (  2.761000)
Total: 3154163000
  2.280000   0.010000   2.290000 (  2.295000)
Total: 3154163000
  2.290000   0.020000   2.310000 (  2.316000)
Total: 3154163000
  2.280000   0.010000   2.290000 (  2.309000)
Total: 3154163000
  2.310000   0.010000   2.320000 (  2.357000)
Sorted
Total: 3154163000
  2.150000   0.030000   2.180000 (  2.239000)
Total: 3154163000
  2.130000   0.000000   2.130000 (  2.146000)
Total: 3154163000
  2.110000   0.010000   2.120000 (  2.120000)
Total: 3154163000
  2.120000   0.010000   2.130000 (  2.122000)
Total: 3154163000
  2.140000   0.010000   2.150000 (  2.116000)