string.c: avoid unnecessary call of str_strlen()

* string.c (rb_strseq_index): refactor and avoid
  call of str_strlen() when offset == 0.
  it will improve performance of String#index and #include?

* benchmark/bm_string_index.rb: benchmark for this change

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60086 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 0 deletions

diff --git a/benchmark/bm_string_index.rb b/benchmark/bm_string_index.rb
new file mode 100644
index 0000000000..7783111082
--- /dev/null
+++ b/benchmark/bm_string_index.rb
@@ -0,0 +1,3 @@
+str1 = "あ" * 1024 + "い" # not single byte optimizable
+str2 = "い"
+100_000.times { str1.index(str2) }