bm.cr

require "./src/benchmark"

def repetition1(ary, times)
  ary = typeof(ary).new(ary.length * times)
  times.times do
    ary += ary
  end
  ary
end

def repetition2(ary, times)
  ary = typeof(ary).new(ary.length * times)
  times.times do
    ary.concat(ary)
  end
  ary
end

def repetition3(ary, times)
  typeof(ary).build(ary.length * times) do |buffer|
    times.times do
      buffer.copy_from(buffer, ary.length)
      buffer += ary.length
    end
    ary.length * times
  end
end

def repetition4(ary, times)
  total_length = ary.length * times
  typeof(ary).build(total_length) do |buffer|
    buffer.copy_from(ary.buffer, ary.length)
    n = ary.length
    while n <= total_length / 2
      (buffer + n).copy_from(buffer, n)
      n *= 2
    end
    (buffer + n).copy_from(buffer, total_length - n)
    total_length
  end
end

[10, 100, 1000, 10000, 10000].each do |n|
  puts "# #{n} times an array of #{n} items"
  ary = (1..n).to_a
  Benchmark.ips do |x|
    x.report("with +=") { repetition1(ary, n) }
    x.report("with concat") { repetition2(ary, n) }
    x.report("with build") { repetition3(ary, n) }
    x.report("with incremental build") { repetition4(ary, n) }
  end
  puts
end

results.txt

# 10 times an array of 10 items
               with += 497041.18 (± 19510.25)  2.54× slower
           with concat 1219959.79 (± 21276.69)  1.03× slower
            with build 1157644.76 (± 47725.08)  1.09× slower
with incremental build 1262033.53 (± 27700.35)       fastest

# 100 times an array of 100 items
               with += 27718.62 (± 805.97)       fastest
           with concat 21107.59 (± 468.77)  1.31× slower
            with build 20454.81 (± 421.33)  1.36× slower
with incremental build 20937.18 (± 483.42)  1.32× slower

# 1000 times an array of 1000 items
               with +=  1354.50 (± 39.02)       fastest
           with concat  1153.33 (± 62.11)  1.17× slower
            with build   715.43 (± 37.43)  1.89× slower
with incremental build   650.58 (± 35.14)  2.08× slower

# 10000 times an array of 10000 items
               with +=    16.49 (±  2.57)       fastest
           with concat    15.71 (±  4.57)  1.05× slower
            with build     8.13 (±  1.70)  2.03× slower
with incremental build     6.58 (±  1.36)  2.50× slower

# 10000 times an array of 10000 items
               with +=    17.20 (±  1.87)       fastest
           with concat    15.94 (±  4.34)  1.08× slower
            with build     8.16 (±  1.80)  2.11× slower
with incremental build     6.70 (±  1.22)  2.57× slower