bytes_terminate() benchmark for the Kaitai Struct Ruby runtime library: https://github.com/kaitai-io/kaitai_struct_ruby_runtime/blob/cc99af6b/lib/kaitai/struct/struct.rb#L437

bench-bytes_terminate.rb

#!/usr/bin/env ruby

=begin
Usage:

    $ ruby bench-bytes_terminate.rb

You need to install https://rubygems.org/gems/benchmark-ips first:

    $ gem install benchmark-ips
=end

require 'benchmark/ips'
require 'json'

TERM_HALFWAY = 1
TERM_END = 2
TERM_MISSING = 3

JSON_TERM_POS_TABLE = {
    'halfway' => TERM_HALFWAY,
    'end' => TERM_END,
    'missing' => TERM_MISSING,
}

conf = JSON.load_file('bench_config.json', {symbolize_names: true})

TERM_POS = JSON_TERM_POS_TABLE.fetch(conf[:term_pos])
raise unless [true, false].include?(conf[:include_term])
INCLUDE_TERM = conf[:include_term]
raise unless conf[:workload_size].is_a?(Integer)
WORKLOAD_SIZE = conf[:workload_size]


def bytes_terminate_old(bytes, term, include_term)
  new_len = 0
  max_len = bytes.length
  while bytes.getbyte(new_len) != term and new_len < max_len
    new_len += 1
  end
  new_len += 1 if include_term and new_len < max_len
  bytes[0, new_len]
end

def bytes_terminate_index(bytes, term, include_term)
  term_index = bytes.index(term.chr)
  if term_index.nil?
    bytes.dup
  else
    bytes[0, term_index + (include_term ? 1 : 0)]
  end
end

def bytes_terminate_index_plus(bytes, term, include_term)
  term_index = bytes.index(term.chr)
  if term_index.nil?
    +bytes
  else
    bytes[0, term_index + (include_term ? 1 : 0)]
  end
end

prng = Random.new

term = prng.rand(256)
repl = 0x00
if repl == term
    repl = 0xff
end
repl = repl.chr(Encoding::ASCII_8BIT)

buf = prng.bytes(WORKLOAD_SIZE)
buf.each_byte.with_index do |b, i|
  buf[i] = repl if b == term
end

if TERM_POS == TERM_HALFWAY
  buf.setbyte(buf.length / 2, term)
elsif TERM_POS == TERM_END
  buf.setbyte(-2, term)
end

exp =
  if TERM_POS == TERM_HALFWAY
    buf.length / 2 + (INCLUDE_TERM ? 1 : 0)
  elsif TERM_POS == TERM_END
    buf.length - 2 + (INCLUDE_TERM ? 1 : 0)
  elsif TERM_POS == TERM_MISSING
    buf.length
  end

act = bytes_terminate_old(buf, term, INCLUDE_TERM).length
raise "expected #{exp} but got #{act}" unless act == exp
act = bytes_terminate_index(buf, term, INCLUDE_TERM).length
raise "expected #{exp} but got #{act}" unless act == exp
act = bytes_terminate_index_plus(buf, term, INCLUDE_TERM).length
raise "expected #{exp} but got #{act}" unless act == exp

Benchmark.ips do |x|
  # x.report("index_plus") do
  #   bytes_terminate_index_plus(buf, term, INCLUDE_TERM)
  # end

  x.report("index") do
    bytes_terminate_index(buf, term, INCLUDE_TERM)
  end

  x.report("old") do
    bytes_terminate_old(buf, term, INCLUDE_TERM)
  end

  x.compare!
end

results-index-vs-old.sh-session

$ echo '{"term_pos": "end", "include_term": false, "workload_size": 1024}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   243.080k i/100ms
                 old     2.299k i/100ms
Calculating -------------------------------------
               index      2.539M (± 1.1%) i/s -     12.883M in   5.074435s
                 old     23.795k (± 1.0%) i/s -    119.548k in   5.024546s

Comparison:
               index:  2539171.4 i/s
                 old:    23795.3 i/s - 106.71x  slower

$ echo '{"term_pos": "halfway", "include_term": false, "workload_size": 2048}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   257.467k i/100ms
                 old     2.335k i/100ms
Calculating -------------------------------------
               index      2.561M (± 0.9%) i/s -     12.873M in   5.026704s
                 old     23.788k (± 2.6%) i/s -    119.085k in   5.010115s

Comparison:
               index:  2561190.3 i/s
                 old:    23787.6 i/s - 107.67x  slower

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 1024}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   418.152k i/100ms
                 old     2.375k i/100ms
Calculating -------------------------------------
               index      4.145M (± 1.1%) i/s -     20.908M in   5.044290s
                 old     23.934k (± 0.5%) i/s -    121.125k in   5.060964s

Comparison:
               index:  4145345.9 i/s
                 old:    23933.7 i/s - 173.20x  slower



$ echo '{"term_pos": "end", "include_term": false, "workload_size": 4096}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   119.994k i/100ms
                 old   576.000 i/100ms
Calculating -------------------------------------
               index      1.872M (± 3.6%) i/s -      9.360M in   5.008434s
                 old      5.980k (± 0.7%) i/s -     29.952k in   5.008889s

Comparison:
               index:  1871917.7 i/s
                 old:     5980.1 i/s - 313.03x  slower

$ echo '{"term_pos": "halfway", "include_term": false, "workload_size": 8192}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   193.497k i/100ms
                 old   585.000 i/100ms
Calculating -------------------------------------
               index      1.930M (± 2.4%) i/s -      9.675M in   5.016233s
                 old      5.863k (± 3.5%) i/s -     29.835k in   5.096169s

Comparison:
               index:  1929994.1 i/s
                 old:     5862.8 i/s - 329.19x  slower

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 4096}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   360.731k i/100ms
                 old   603.000 i/100ms
Calculating -------------------------------------
               index      3.565M (± 1.0%) i/s -     18.037M in   5.060550s
                 old      6.012k (± 0.7%) i/s -     30.150k in   5.015320s

Comparison:
               index:  3564520.8 i/s
                 old:     6011.9 i/s - 592.91x  slower



$ echo '{"term_pos": "end", "include_term": false, "workload_size": 16384}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index    42.668k i/100ms
                 old   149.000 i/100ms
Calculating -------------------------------------
               index    303.517k (± 2.6%) i/s -      1.536M in   5.064298s
                 old      1.486k (± 1.2%) i/s -      7.450k in   5.013941s

Comparison:
               index:   303517.2 i/s
                 old:     1486.1 i/s - 204.24x  slower

$ echo '{"term_pos": "halfway", "include_term": false, "workload_size": 32768}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index    32.236k i/100ms
                 old   148.000 i/100ms
Calculating -------------------------------------
               index    325.857k (± 3.0%) i/s -      1.644M in   5.049964s
                 old      1.491k (± 1.0%) i/s -      7.548k in   5.061962s

Comparison:
               index:   325856.6 i/s
                 old:     1491.3 i/s - 218.51x  slower

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 16384}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
               index   279.347k i/100ms
                 old   136.000 i/100ms
Calculating -------------------------------------
               index      2.833M (± 0.8%) i/s -     14.247M in   5.029648s
                 old      1.504k (± 0.8%) i/s -      7.616k in   5.062980s

Comparison:
               index:  2832731.1 i/s
                 old:     1504.3 i/s - 1883.03x  slower

results-index_plus-vs-index.sh-session

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 1024}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
          index_plus   422.285k i/100ms
               index   331.757k i/100ms
Calculating -------------------------------------
          index_plus      4.334M (± 0.9%) i/s -     21.959M in   5.067086s
               index      3.806M (± 0.9%) i/s -     19.242M in   5.055957s

Comparison:
          index_plus:  4334014.0 i/s
               index:  3806103.2 i/s - 1.14x  slower

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 4096}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
          index_plus   407.681k i/100ms
               index   362.686k i/100ms
Calculating -------------------------------------
          index_plus      4.099M (± 0.5%) i/s -     20.792M in   5.071932s
               index      3.609M (± 0.6%) i/s -     18.134M in   5.025432s

Comparison:
          index_plus:  4099483.6 i/s
               index:  3608631.0 i/s - 1.14x  slower

$ echo '{"term_pos": "missing", "include_term": false, "workload_size": 16384}' > bench_config.json && ruby bench-bytes_terminate.rb
ruby 3.3.4 (2024-07-09 revision be1089c8ec) [x86_64-linux]
Warming up --------------------------------------
          index_plus   321.927k i/100ms
               index   285.162k i/100ms
Calculating -------------------------------------
          index_plus      3.211M (± 0.9%) i/s -     16.096M in   5.013197s
               index      2.838M (± 1.7%) i/s -     14.258M in   5.025916s

Comparison:
          index_plus:  3211037.2 i/s
               index:  2837859.8 i/s - 1.13x  slower