Improve performance of reading escaped string

[Watson1978]

This patch will improve the performance of reading escaped string by using a lookup table.

−	before	after	result
Oj.load	601.508	654.004	1.087x

Environment

• Linux
  • Manjaro Linux x86_64
  • Kernel: 6.12.4-1-MANJARO
  • AMD Ryzen 9 8945HS
  • gcc version 14.2.1
  • Ruby 3.4.1

Code

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'benchmark-ips'
  gem 'oj'
end

# https://github.com/miloyip/nativejson-benchmark/blob/master/data/twitter.json
json = File.read('twitter.json')

Benchmark.ips do |x|
  x.time = 10
  x.report('Oj.load compat') { Oj.load(json, mode: :compat) }
end

Before

$ ruby json_load.rb
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
Warming up --------------------------------------
      Oj.load compat    59.000 i/100ms
Calculating -------------------------------------
      Oj.load compat    601.508 (± 1.2%) i/s    (1.66 ms/i) -      6.018k in  10.006395s

After

$ ruby json_load.rb
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
Warming up --------------------------------------
      Oj.load compat    64.000 i/100ms
Calculating -------------------------------------
      Oj.load compat    654.004 (± 1.7%) i/s    (1.53 ms/i) -      6.592k in  10.082170s

[ohler55]

Nice. Arrigato.