[llvm-dev] Improvements to std::find and std::count

Daniel Cooke via llvm-dev llvm-dev at lists.llvm.org
Sat Apr 29 07:13:02 PDT 2017


I recently posted a question on StackOverflow regarding the performance of std::find and std::count when provided with char* input: http://stackoverflow.com/questions/43483378/why-arent-stdcount-and-stdfind-optimised-to-use-memchr <http://stackoverflow.com/questions/43483378/why-arent-stdcount-and-stdfind-optimised-to-use-memchr>.

I would propose adding overloads of these functions for char* and const char* inputs that delegate to memchr, something like:

inline const char* find(const char* first, const char* const last, const char value)
	const auto result = std::memchr(first, value, last - first);
	return result != nullptr ? static_cast<const char*>(result) : last;

inline typename std::iterator_traits<const char*>::difference_type
count(const char* first, const char* const last, const char value)
	typename std::iterator_traits<const char*>::difference_type result {0};
	while (first && first != last) {
		if ((first = static_cast<const char*>(std::memchr(first, value, last - first)))) {
	return result;

I’ve never contributed to LLVM, so I’m not sure how to proceed, if this is a change that is likely to be accepted?


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