From a83c91dd7ab8ebf3f1b89a56280bdf7aab0d882f Mon Sep 17 00:00:00 2001
From: Yusuke Endoh <mame@ruby-lang.org>
Date: Mon, 21 Oct 2024 18:25:09 +0900
Subject: [PATCH] Fix an off-by-one error of own memrchr implementation

and make it support `search_len == 0`, just for the case

Ref [Bug #20796]
---
 string.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/string.c b/string.c
index b8213ea085..11a2ec1b71 100644
--- a/string.c
+++ b/string.c
@@ -4548,9 +4548,9 @@ static void*
 memrchr(const char *search_str, int chr, long search_len)
 {
     const char *ptr = search_str + search_len;
-    do {
+    while (ptr > search_str) {
         if ((unsigned char)*(--ptr) == chr) return (void *)ptr;
-    } while (ptr >= search_str);
+    }
 
     return ((void *)0);
 }