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src: optimize utf-8 byte length calculation using simdutf #61601

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src: optimize utf-8 byte length calculation using simdutf #61601

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ef28e76
src: optimize utf-8 byte length calculation using simdutf
mertcanaltin Mar 4, 2026
753dbd0
src: optimize utf-8 byte length calculation using simdutf
mertcanaltin Mar 5, 2026
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75 changes: 31 additions & 44 deletions src/node_buffer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -761,9 +761,27 @@ void StringWrite(const FunctionCallbackInfo<Value>& args) {
void SlowByteLengthUtf8(const FunctionCallbackInfo<Value>& args) {
CHECK(args[0]->IsString());

// Fast case: avoid StringBytes on UTF8 string. Jump to v8.
size_t result = args[0].As<String>()->Utf8LengthV2(args.GetIsolate());
args.GetReturnValue().Set(static_cast<uint64_t>(result));
Isolate* isolate = args.GetIsolate();
Local<String> source = args[0].As<String>();

static constexpr int kSmallStringThreshold = 128;
int length = source->Length();

if (length <= kSmallStringThreshold || source->IsOneByte()) {
args.GetReturnValue().Set(
static_cast<uint64_t>(source->Utf8LengthV2(isolate)));
return;
}

String::ValueView view(isolate, source);
auto data = reinterpret_cast<const char16_t*>(view.data16());
if (simdutf::validate_utf16(data, length)) {
args.GetReturnValue().Set(
static_cast<uint64_t>(simdutf::utf8_length_from_utf16(data, length)));
return;
}
args.GetReturnValue().Set(
static_cast<uint64_t>(source->Utf8LengthV2(isolate)));
}

uint32_t FastByteLengthUtf8(
Expand All @@ -776,49 +794,19 @@ uint32_t FastByteLengthUtf8(
CHECK(sourceValue->IsString());
Local<String> sourceStr = sourceValue.As<String>();

if (!sourceStr->IsExternalOneByte()) {
static constexpr int kSmallStringThreshold = 128;
int length = sourceStr->Length();

if (length <= kSmallStringThreshold || sourceStr->IsOneByte()) {
return sourceStr->Utf8LengthV2(isolate);
}
auto source = sourceStr->GetExternalOneByteStringResource();
// For short inputs, the function call overhead to simdutf is maybe
// not worth it, reserve simdutf for long strings.
if (source->length() > 128) {
return simdutf::utf8_length_from_latin1(source->data(), source->length());
}

uint32_t length = source->length();
const auto input = reinterpret_cast<const uint8_t*>(source->data());

uint32_t answer = length;
uint32_t i = 0;

auto pop = [](uint64_t v) {
return static_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);
String::ValueView view(isolate, sourceStr);
auto data = reinterpret_cast<const char16_t*>(view.data16());
if (simdutf::validate_utf16(data, length)) {
return simdutf::utf8_length_from_utf16(data, length);
}
for (; i + 8 <= length; i += 8) {
uint64_t v;
memcpy(&v, input + i, 8);
answer += pop(v);
}
for (; i + 1 <= length; i += 1) {
answer += input[i] >> 7;
}

return answer;
return sourceStr->Utf8LengthV2(isolate);
}

static CFunction fast_byte_length_utf8(CFunction::Make(FastByteLengthUtf8));
Expand Down Expand Up @@ -1252,8 +1240,7 @@ static void IsAscii(const FunctionCallbackInfo<Value>& args) {
env, "Cannot validate on a detached buffer");
}

args.GetReturnValue().Set(
!simdutf::validate_ascii_with_errors(abv.data(), abv.length()).error);
args.GetReturnValue().Set(simdutf::validate_ascii(abv.data(), abv.length()));
}

void SetBufferPrototype(const FunctionCallbackInfo<Value>& args) {
Expand Down
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