steps_no_flaws.cr

require "benchmark"

struct 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 835.01M (  1.20ns) (± 7.91%)  0.0B/op   1.01× slower
#  step_from_explicit_literal 834.18M (  1.20ns) (± 8.61%)  0.0B/op   1.01× slower
# step_from_explicit variable 830.88M (  1.20ns) (± 8.82%)  0.0B/op   1.02× slower
#  times explicit single step 845.11M (  1.18ns) (± 7.10%)  0.0B/op        fastest
#     times step from stride 836.71M (  1.20ns) (±10.16%)  0.0B/op   1.01× slower