Issue #8129 has been updated by charliesome (Charlie Somerville).

Status changed from Open to Rejected

When all the characters in a string are ASCII characters (single bytes), the byte index for any given character can be calculated in constant time.

When the string contains multibyte characters, finding the byte index given a character index becomes O(n).

If you need fast character indexing, try splitting the string into an array or characters.
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Bug #8129: String#index has drastically different performance when a single unicode character is included
https://bugs.ruby-lang.org/issues/8129#change-37748

Author: zmoazeni (Zach Moazeni)
Status: Rejected
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: 2.0.0-p0


I created a simple ruby script:

```
#! /usr/bin/env ruby
 
raise "need a file name" unless ARGV[0]
contents = File.read(ARGV[0])
 
326_000.times do |i|
  contents[(i + 23) % contents.size]
end
```

And I uploaded two files below. One is all ASCII characters and the other has a single Unicode character in the first line (an "em dash").

String#index has dramatically different performance for the two strings. Locally, I'm seeing ~1.5 seconds with all_ascii.css and ~30 seconds with one_unicode.css on 1.9.3-p385. It gets worse with ruby 2.0, all_ascii.css still takes ~1 sec, but one_unicode.css takes ~2.5 minutes!

Any idea why the performance is so dramatically different between the two?


-- 
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