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Feature #13750

open

Improve String#casecmp? and Symbol#casecmp? performance with ASCII string

Feature #13750: Improve String#casecmp? and Symbol#casecmp? performance with ASCII string

Added by watson1978 (Shizuo Fujita) over 8 years ago. Updated almost 5 years ago.

Status:
Open
Assignee:
-
Target version:
-
[ruby-core:82086]

Description

I think String#casecmp and String#casecmp? are similar methods. But they have different performance with ASCII strings.

It seems that String#casecmp handles ASCII string only, but it is faster than String#casecmp?.

This patch uses the code of String#casecmp on String#casecmp? for ASCII strings. However, it introduces a minor penalty for UTF8 strings due to detection of ASCII/UTF8 strings.

String#casecmp? ASCII -> 61.3 % up String#casecmp? UTF8 -> 1.3 % down Symbol#casecmp? ASCII -> 80.0 % up Symbol#casecmp? UTF8 -> 4.0 % down

Before

Calculating ------------------------------------- String#casecmp 5.961M (± 3.8%) i/s - 29.838M in 5.017907s String#casecmp? ASCII 3.530M (± 8.6%) i/s - 17.554M in 5.034848s String#casecmp? UTF8 1.252M (± 7.4%) i/s - 6.213M in 5.012168s Symbol#casecmp 8.555M (± 2.4%) i/s - 42.822M in 5.009280s Symbol#casecmp? ASCII 4.235M (± 9.7%) i/s - 20.824M in 5.001368s Symbol#casecmp? UTF8 1.329M (± 0.1%) i/s - 6.704M in 5.043725s

After

Calculating ------------------------------------- String#casecmp 5.984M (± 6.4%) i/s - 29.829M in 5.020331s String#casecmp? ASCII 5.658M (± 1.5%) i/s - 28.308M in 5.004547s String#casecmp? UTF8 1.215M (± 4.3%) i/s - 6.132M in 5.060292s Symbol#casecmp 8.651M (± 0.9%) i/s - 43.313M in 5.007215s Symbol#casecmp? ASCII 7.462M (± 0.5%) i/s - 37.489M in 5.023892s Symbol#casecmp? UTF8 1.275M (± 0.2%) i/s - 6.444M in 5.052743s

Test code

require 'benchmark/ips' Benchmark.ips do |x| x.report "String#casecmp" do |loop| loop.times { "aBcDeF".casecmp("abcdefg") } end x.report "String#casecmp? ASCII" do |loop| loop.times { "aBcDeF".casecmp?("abcdefg") } end x.report "String#casecmp? UTF8" do |loop| loop.times { "\u{e4 f6 fc}".casecmp?("\u{c4 d6 dc}") } end x.report "Symbol#casecmp" do |loop| loop.times { :aBcDeF.casecmp(:abcdefg) } end x.report "Symbol#casecmp? ASCII" do |loop| loop.times { :aBcDeF.casecmp?(:abcdefg) } end x.report "Symbol#casecmp? UTF8" do |loop| loop.times { :"\u{e4 f6 fc}".casecmp?(:"\u{c4 d6 dc}") } end end

Patch

https://github.com/ruby/ruby/pull/1668

Updated by watson1978 (Shizuo Fujita) over 8 years ago Actions
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 #1 [ruby-core:82087]

Because String#casecmp? duplicates object at rb_str_downcase() every time, so String#casecmp? is slower than String#casecmp?

Updated by jeremyevans0 (Jeremy Evans) over 6 years ago Actions
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 #2

  • Tracker changed from Bug to Feature
  • Backport deleted (2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN)

Updated by sawa (Tsuyoshi Sawada) over 5 years ago Actions
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 #4

  • Description updated (diff)

Updated by naruse (Yui NARUSE) almost 5 years ago Actions
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 #5 [ruby-core:102224]

When you avoid that case, you have a option around coderange: coderange is a cached information whether the string contains (1) only ASCII 7 bit characters (2) also has 8 bit characters (3) broken byte sequence (4) unknown. Some strings are already scanned its coderange and caches it in a string object, but others are not. Whether this casecmp? optimization uses the cache and not scan string if the cache doesn't exist, or scan if it doesn't have a cache. If you use the cache, I wonder whether strings in real applications have cache or not. If you scan, I wonder if it still gets faster.

Imagine casecmp? with following chatacters:

  • "a" * 100000 + "A"
  • "a" * 100000 + "a"
  • "a" * 100000 + "À"
  • "a" * 100000 + "à"
  • "ab"
    Using rb_enc_str_asciionly_p enforces to scan whole strings if it doesn't have coderange cache, and it can be overhead.

To avoid such trade off, I think you need to implement　integrated casecmp with rb_str_casemap.

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