buffer: optimize byteLength for short strings

PR-URL: #54345
Reviewed-By: Daniel Lemire <daniel@lemire.me>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: ronag

src/node_buffer.cc

@@ -35,6 +35,7 @@
 #include"v8-fast-api-calls.h"
 #include"v8.h"
 
+#include<stdint.h>
 #include<climits>
 #include<cstring>
 #include"nbytes.h"
@@ -741,13 +742,40 @@ uint32_t FastByteLengthUtf8(Local<Value> receiver,
 if (source.length > 128) {
 returnsimdutf::utf8_length_from_latin1(source.data, source.length);
  }
+
 uint32_t length = source.length;
-uint32_t result = length;
-constuint8_t* data = reinterpret_cast<constuint8_t*>(source.data);
-for (uint32_t i = 0; i < length; ++i) {
- result += (data[i] >> 7);
+constauto input = reinterpret_cast<constuint8_t*>(source.data);
+
+uint32_t answer = length;
+uint32_t i = 0;
+
+auto pop = [](uint64_t v) {
+returnstatic_cast<size_t>(((v >> 7) & UINT64_C(0x0101010101010101)) *
+UINT64_C(0x0101010101010101) >>
+56);
+ };
+
+for (; i + 32 <= length; i += 32) {
+uint64_t v;
+memcpy(&v, input + i, 8);
+ answer += pop(v);
+memcpy(&v, input + i + 8, 8);
+ answer += pop(v);
+memcpy(&v, input + i + 16, 8);
+ answer += pop(v);
+memcpy(&v, input + i + 24, 8);
+ answer += pop(v);
+ }
+for (; i + 8 <= length; i += 8) {
+uint64_t v;
+memcpy(&v, input + i, 8);
+ answer += pop(v);
  }
-return result;
+for (; i + 1 <= length; i += 1) {
+ answer += input[i] >> 7;
+ }
+
+return answer;
 }
 
 static v8::CFunction fast_byte_length_utf8(