jruby
           unpack h*      2.961M (? 4.8%) i/s -     14.738M in   4.995894s
          unpack1 h*    591.196k (? 8.0%) i/s -      2.946M in   5.019534s
           unpack C*      2.628M (? 5.9%) i/s -     13.082M in   5.000418s
          unpack1 C*    642.124k (? 3.2%) i/s -      3.227M in   5.032145s
            unpack m      2.878M (? 5.8%) i/s -     14.328M in   5.002753s
           unpack1 m    616.794k (? 2.4%) i/s -      3.095M in   5.020186s
        unpack block    542.986k (? 7.7%) i/s -      2.697M in   5.004756s
       unpack1 block    522.406k (? 3.7%) i/s -      2.623M in   5.028202s

jruby + patch
           unpack h*      2.904M (? 5.3%) i/s -     14.453M in   4.994340s
          unpack1 h*      3.153M (? 4.2%) i/s -     15.747M in   5.005090s
           unpack C*      2.441M (? 5.9%) i/s -     12.199M in   5.021349s
          unpack1 C*      3.673M (? 6.2%) i/s -     18.317M in   5.011808s
            unpack m      2.821M (? 3.9%) i/s -     14.101M in   5.008559s
           unpack1 m      3.037M (? 5.6%) i/s -     15.123M in   5.007571s
        unpack block    578.569k (? 4.9%) i/s -      2.897M in   5.022202s
       unpack1 block      1.871M (? 3.6%) i/s -      9.381M in   5.021880s

ruby 2.7
           unpack h*      2.600M (±16.2%) i/s -     12.405M in   5.013330s
          unpack1 h*      3.718M (±13.1%) i/s -     18.004M in   5.000438s
           unpack C*      1.245M (±13.6%) i/s -      6.107M in   5.026846s
          unpack1 C*      4.960M (±11.6%) i/s -     24.207M in   5.001412s
            unpack m      3.125M (±14.5%) i/s -     15.193M in   4.997823s
           unpack1 m      4.479M (±13.1%) i/s -     21.788M in   4.998978s
        unpack block      2.492M (±11.5%) i/s -     12.306M in   5.015661s
       unpack1 block      3.790M (±13.4%) i/s -     18.542M in   5.010570s

truffleruby 19.0.0
           unpack h*      9.193M (±23.8%) i/s -     35.973M in   4.990790s
          unpack1 h*      8.758M (±24.5%) i/s -     31.961M in   5.010966s
           unpack C*     12.899M (±18.6%) i/s -     51.961M in   5.096628s
          unpack1 C*     13.891M (±22.1%) i/s -     49.695M in   4.995458s
            unpack m      3.773M (±17.8%) i/s -     17.240M in   5.141586s
           unpack1 m      3.725M (±20.4%) i/s -     15.927M in   5.029317s
        unpack block      4.120M (±28.6%) i/s -     15.636M in   5.007153s
       unpack1 block      8.467M (±20.2%) i/s -     33.450M in   5.004004s

require 'base64'
require 'benchmark/ips'

STRING = "foobarbaz".freeze

def unpack_block
  STRING.unpack('b5B8') { |x| return x }
end

def unpack1_block
  STRING.unpack1('b5B8') { |x| return x }
end

Benchmark.ips do |x|
  x.report('unpack h*') { STRING.unpack('h*').first }
  x.report('unpack1 h*') { STRING.unpack1('h*') }
  x.report('unpack C*') { STRING.unpack("C*").first }
  x.report('unpack1 C*') { STRING.unpack1("C*") }
  x.report('unpack m') { STRING.unpack("m").first }
  x.report('unpack1 m') { STRING.unpack1("m") }
  x.report('unpack block') { unpack_block }
  x.report('unpack1 block') { unpack1_block }
end