Optimize Lookups for ruby-talk 382374

lv.rb

require 'benchmark'

REP = 10

Benchmark.bm 20 do |x|
  pixels = Array.new(258000, rand(256)).freeze

  old_lv = nil

  x.report "old prep" do
    # Set up example arrays to test the algorithm:
    REP.times do
      old_lv = Array.new
      old_lv << Array.new(256, 0)
      old_lv << Array.new(256, 1)
      old_lv << Array.new(256, 2)
    end
  end

  x.report "old" do
    REP.times do
      rgb = Array.new(pixels.length*3)

      # The PALETTE transformation algorithm:
      pixels.each_index do |i|
       rgb[i*3] = old_lv[0][pixels[i]]
       rgb[(i*3)+1] = old_lv[1][pixels[i]]
       rgb[(i*3)+2] = old_lv[2][pixels[i]]
      end
    end
  end

  new_lv = nil

  x.report "new prep" do
    REP.times do
      # Set up example arrays to test the algorithm:
      new_lv = Array.new(256) { [0,1,2] }
    end
  end

  x.report "new" do
    REP.times do
      rgb = Array.new(pixels.length*3)

      # The PALETTE transformation algorithm:
      pixels.each_with_index do |pix, i|
       rgb[i * 3, 3] = new_lv[pix]
      end
    end
  end

end