From 381910a51d415007007fee9a723b83c4547ce6e7 Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <tim.ledbetter@ladybird.org>
Date: Mon, 11 May 2026 09:34:42 +0100
Subject: [PATCH] AK: Use `memchr` for `Utf8View::contains()` ASCII fast path

The libc implementation of `memchr` uses SIMD, so is significantly
faster than looping over individual bytes.
---
 AK/Utf8View.cpp | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/AK/Utf8View.cpp b/AK/Utf8View.cpp
index bfd7fd95e3..791f1e2c95 100644
--- a/AK/Utf8View.cpp
+++ b/AK/Utf8View.cpp
@@ -126,18 +126,15 @@ bool Utf8View::starts_with(Utf8View const& start) const
 bool Utf8View::contains(u32 needle) const
 {
     if (needle <= 0x7f) {
-        // OPTIMIZATION: Fast path for ASCII
-        for (u8 code_point : as_string()) {
-            if (code_point == needle)
-                return true;
-        }
-    } else {
-        for (u32 code_point : *this) {
-            if (code_point == needle)
-                return true;
-        }
+        // OPTIMIZATION: An ASCII byte can only appear as itself in valid UTF-8, so memchr is safe here.
+        auto bytes = as_string();
+        return memchr(bytes.characters_without_null_termination(), needle, bytes.length()) != nullptr;
     }
 
+    for (u32 code_point : *this) {
+        if (code_point == needle)
+            return true;
+    }
     return false;
 }