String#index has drastically different performance when a single unicode character is included
I created a simple ruby script:
#! /usr/bin/env ruby
raise "need a file name" unless ARGV
contents = File.read(ARGV)
326_000.times do |i|
contents[(i + 23) % contents.size]
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?