From: Kornelius Kalnbach <murphy@...>
Date: 2006-11-11T15:36:47+09:00
Subject: What does rb_memsearch do?

Hello!

I've been wondering what the function rb_memsearch does. It is  
defined in
re.c (line 101). It is only used for rb_str_index, and I can't figure  
out
what it does.

Is it an exotic string search algorithm? Whatever it does, it's very  
slow,
slower then the naive memcmp implementation from memcmp.c.

Benchmark attached.
[murphy]

require 'benchmark'

N = 100_000
sub = 'That is a foo.'
s = 'That is a bar. ' * 10 + sub

Benchmark.bm 20 do |bm|
   bm.report 'String#index' do
     N.times do
       s.index sub
     end
   end

   sub.reverse!
   s.reverse!
   bm.report 'String#rindex' do
     N.times do
       s.rindex sub
     end
   end
end
# >>                           user     system      total        real
# >> String#index          0.170000   0.000000   0.170000  
(  0.163899)  # OK
# >> String#rindex         0.710000   0.000000   0.710000  
(  0.704800)  # why?