From 31f2d936573e90059cf413f07705aa1d29b44fdd Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Wed, 10 Jan 2024 15:36:07 +0900
Subject: [PATCH] string.c (bytes2chars): skip calling mrb_utf8len() if
 possible

If (ch < 0x80) the length of the character (in bytes) should be 1, so we
don't have to call mrb_utf8len().
---
 src/string.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/string.c b/src/string.c
index 411de76e6..c6f419247 100644
--- a/src/string.c
+++ b/src/string.c
@@ -358,7 +358,8 @@ bytes2chars(mrb_value s, mrb_int bi)
   mrb_int i;
 
   for (i = 0; p < pivot; i++) {
-    p += mrb_utf8len(p, e);
+    if ((*p & 0x80) == 0) p++;
+    else p += mrb_utf8len(p, e);
   }
   if (p != pivot) return -1;
   return i;