From 110e88b19166bd7ae1984866ad57259a12f8789a Mon Sep 17 00:00:00 2001
From: Robert Nagy <ronagy@icloud.com>
Date: Mon, 12 Aug 2024 23:10:08 +0200
Subject: [PATCH] buffer: optimize byteLength for short strings

PR-URL: https://github.com/nodejs/node/pull/54345
---
 src/node_buffer.cc | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/node_buffer.cc b/src/node_buffer.cc
index 6e141b974131cc..b46864a3a74f92 100644
--- a/src/node_buffer.cc
+++ b/src/node_buffer.cc
@@ -35,6 +35,7 @@
 #include "v8-fast-api-calls.h"
 #include "v8.h"
 
+#include <bit>
 #include <climits>
 #include <cstring>
 #include "nbytes.h"
@@ -752,12 +753,25 @@ uint32_t FastByteLengthUtf8(Local<Value> receiver,
   if (source.length > 128) {
     return simdutf::utf8_length_from_latin1(source.data, source.length);
   }
+
   uint32_t length = source.length;
   uint32_t result = length;
-  const uint8_t* data = reinterpret_cast<const uint8_t*>(source.data);
-  for (uint32_t i = 0; i < length; ++i) {
+  const auto data = reinterpret_cast<const uint8_t*>(source.data);
+
+  uint32_t i = 0;
+  const auto length8 = length & ~0x7;
+  while (i < length8) {
+    uint64_t x;
+    memcpy(&x, data + i, sizeof(uint64_t));
+    result += std::popcount(x & 0x8080808080808080);
+    i += 8;
+  }
+
+  while (i < length) {
     result += (data[i] >> 7);
+    i++;
   }
+
   return result;
 }