From f8b9464118e584230ec3c76d39a19cc551fe8a5e Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Tue, 17 May 2022 07:18:44 +0900
Subject: [PATCH] string.rb (each_line): use byteindex for performance; fix
 #4522

Character-wise String#index method calculate UTF-8 character width
numerous times if the string is long.
---
 mrblib/string.rb | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mrblib/string.rb b/mrblib/string.rb
index 84e7530c9..94a593f48 100644
--- a/mrblib/string.rb
+++ b/mrblib/string.rb
@@ -30,10 +30,10 @@ class String
     self_len = length
     sep_len = separator.length
 
-    while (pointer = string.index(separator, start))
+    while (pointer = string.byteindex(separator, start))
       pointer += sep_len
-      pointer += 1 while paragraph_mode && string[pointer] == "\n"
-      block.call(string[start, pointer - start])
+      pointer += 1 while paragraph_mode && string.getbyte(pointer) == 10 # 10 == \n
+      block.call(string.byteslice(start, pointer - start))
       start = pointer
     end
     return self if start == self_len