timings2.cr

require "benchmark"

class Foo
  def initialize(@size : Int32, @stride : Int32)
  end

  def step_from_class
    0.step(to: @size, by: @stride) do |i|
      yield i
    end
  end

  def step_from_explicit(n : Int32, step : Int32)
    0.step(to: n, by: step) do |i|
      yield i
    end
  end

  def times_explicit_single_step
    i = @size ^ @size
    while i < @size
      yield i
      i += 1
    end
  end

  def times_step_from_stride
    i = @size ^ @size
    while i < @size
      yield i
      i += @stride
    end
  end
end

a = 0

Benchmark.ips do |b|
  b.report("step from class") do
    n = 100_000
    step = 1
    f = Foo.new(n, step)
    f.step_from_class { |i| a &+= i }
  end
  b.report("step_from_explicit_literal") do
    n = 100_000
    step = 1
    f = Foo.new(n, step)
    f.step_from_explicit(100_000, 1) { |i| a &+= i }
  end
  b.report("step_from_explicit variable") do
    n = 100_000
    step = 1
    f = Foo.new(n, step)
    f.step_from_explicit(n, step) { |i| a &+= i }
  end
  b.report("times explicit single step") do
    n = 100_000
    step = 1
    f = Foo.new(n, step)
    f.times_explicit_single_step { |i| a &+= i }
  end
  b.report("times step from stride") do
    n = 100_000
    step = 1
    f = Foo.new(n, step)
    f.times_step_from_stride { |i| a &+= i }
  end
end

puts a

# step from class   9.78k (102.29µs) (± 6.42%)  16.0B/op  7579.76× slower
# step_from_explicit_literal  74.10M ( 13.50ns) (±10.92%)  16.0B/op          fastest
# step_from_explicit variable  71.71M ( 13.94ns) (±11.56%)  16.0B/op     1.03× slower
# times explicit single step  24.85k ( 40.24µs) (± 8.88%)  16.0B/op  2981.49× slower
# times step from stride  15.72k ( 63.62µs) (± 2.88%)  16.0B/op  4714.64× slower