Array rotation

benchmark.cr

require "benchmark"

class Array
  def new_rotate!(n = 1)
    return self if empty?
    sz = self.size
    n %= sz
    return self if n == 0

    tmp = Slice.new(to_unsafe, sz)
    tmp[0...n].reverse!
    tmp[n..-1].reverse!
    tmp.reverse!

    self
  end
end

x3 = (0...3).to_a
x10 = (0...10).to_a
x100 = (0...100).to_a
x1000 = (0...1000).to_a

Benchmark.ips do |x|
  x.report("3 rotate! 2") { x3.rotate!(2) }
  x.report("3 new_rotate! 2") { x3.new_rotate!(2) }
end

Benchmark.ips do |x|
  x.report("10 rotate! 3") { x10.rotate!(3) }
  x.report("10 new_rotate! 3") { x10.new_rotate!(3) }
end

Benchmark.ips do |x|
  x.report("100 rotate! 30") { x100.rotate!(30) }
  x.report("100 new_rotate! 30") { x100.new_rotate!(30) }
end

Benchmark.ips do |x|
  x.report("1000 rotate! 300") { x1000.rotate!(300) }
  x.report("1000 new_rotate! 300") { x1000.new_rotate!(300) }
end

result

    3 rotate! 2   8.92M (112.06ns) (± 6.49%)  49.0B/op   3.40× slower
3 new_rotate! 2  30.34M ( 32.96ns) (± 2.97%)   0.0B/op        fastest
    10 rotate! 3   9.67M (103.43ns) (± 4.34%)  65.0B/op   2.58× slower
10 new_rotate! 3  24.96M ( 40.07ns) (± 2.89%)   0.0B/op        fastest
    100 rotate! 30   5.12M (195.25ns) (± 5.70%)  161B/op   1.49× slower
100 new_rotate! 30   7.61M (131.47ns) (± 2.62%)  0.0B/op        fastest
    1000 rotate! 300 352.55k (  2.84µs) (± 2.22%)  2.03kB/op   3.05× slower
1000 new_rotate! 300   1.07M (931.43ns) (± 2.97%)    0.0B/op        fastest