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Make JSStringToSTLString 23x faster #26955

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Make JSStringToSTLString 23x faster #26955

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c197db7
Update JSCRuntime.cpp
radex Oct 22, 2019
719e60c
JSStringToSTLString - use std::unique_ptr, small string optimization
radex Oct 24, 2019
1e922cf
Restructure JSStringToSTLString and add comments
motiz88 Jan 27, 2020
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17 changes: 14 additions & 3 deletions ReactCommon/jsi/JSCRuntime.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -285,10 +285,21 @@ class JSCRuntime : public jsi::Runtime {
// JSStringRef utilities
namespace {
std::string JSStringToSTLString(JSStringRef str) {
// Small string optimization: Avoid one heap allocation for strings that fit
// in stackBuffer.size() bytes of UTF-8 (including the null terminator).
std::array<char, 20> stackBuffer;
std::unique_ptr<char[]> heapBuffer;
char* buffer;
size_t maxBytes = JSStringGetMaximumUTF8CStringSize(str);
std::vector<char> buffer(maxBytes);
JSStringGetUTF8CString(str, buffer.data(), maxBytes);
return std::string(buffer.data());
if (maxBytes <= stackBuffer.size()) {
buffer = stackBuffer.data();
} else {
heapBuffer = std::make_unique<char[]>(maxBytes);
buffer = heapBuffer.get();
}
size_t actualBytes = JSStringGetUTF8CString(str, buffer, maxBytes);
// NOTE: By definition, maxBytes >= actualBytes >= 1.
return std::string(buffer, actualBytes - 1);
}

JSStringRef getLengthString() {
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