benchmark scan vs unpack for utf-8 string

bench.txt

$ ruby -v -Ku scan_unpack_banch.rb                                           ~
ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]
Rehearsal -----------------------------------------------------
scan each len:      0.140000   0.000000   0.140000 (  0.141777)
unpack each len:    0.070000   0.000000   0.070000 (  0.064889)
scan total len:     0.110000   0.000000   0.110000 (  0.108800)
unpack total len:   0.000000   0.000000   0.000000 (  0.004272)
-------------------------------------------- total: 0.320000sec

                        user     system      total        real
scan each len:      0.130000   0.000000   0.130000 (  0.131575)
unpack each len:    0.070000   0.000000   0.070000 (  0.065743)
scan total len:     0.100000   0.000000   0.100000 (  0.099954)
unpack total len:   0.010000   0.000000   0.010000 (  0.004284)

Results:
true
true

scan_unpack_banch.rb

require 'benchmark'

TIMES = 200
string = "a¢あ𤭢" * TIMES

r1, r2, r3, r4 = nil, nil, nil, nil

Benchmark.bmbm do |x|
  x.report("scan each len:") { TIMES.times { r1 = string.scan(/./mu).map { |c| c.length } } }
  x.report("unpack each len:"){ TIMES.times { r2 = string.unpack("U*").map { |c|
    # From http://en.wikipedia.org/wiki/UTF-8#Description
    if c <= 0x7F
      1
    elsif c <= 0x7FF
      2
    elsif c <= 0xFFFF
      3
    elsif c <= 0x1FFFFF
      4
    elsif c <= 0x3FFFFFF
      5
    else
      6
    end
  } } }

  x.report("scan total len:") { TIMES.times { r3 = string.scan(/./mu)[0,3].to_s.length } }
  x.report("unpack total len:") { TIMES.times { r4 = string.unpack("U*")[0,3].pack("U*").length } }
end

puts
puts "Results:"
p r1 == r2
p r3 == r4