ClickHouse/dbms/include/DB/Core/StringRef.h

#pragma once

#include <string.h>
#include <city.h>

#include <string>
#include <vector>

#include <functional>
#include <ostream>


/// Штука, чтобы не создавать строки для поиска подстроки в хэш таблице.
struct StringRef
{
	const char * data = nullptr;
	size_t size = 0;

	StringRef(const char * data_, size_t size_) : data(data_), size(size_) {}
	StringRef(const unsigned char * data_, size_t size_) : data(reinterpret_cast<const char *>(data_)), size(size_) {}
	StringRef(const std::string & s) : data(s.data()), size(s.size()) {}
	StringRef() {}

	std::string toString() const { return std::string(data, size); }
};

typedef std::vector<StringRef> StringRefs;

inline bool operator==(StringRef lhs, StringRef rhs)
{
	/// Так почему-то быстрее, чем return lhs.size == rhs.size && 0 == memcmp(lhs.data, rhs.data, lhs.size);

	if (lhs.size != rhs.size)
		return false;

	for (size_t pos = 0; pos < lhs.size; ++pos)
		if (lhs.data[pos] != rhs.data[pos])
			return false;

	return true;
}

inline bool operator!=(StringRef lhs, StringRef rhs)
{
	return !(lhs == rhs);
}

inline bool operator<(StringRef lhs, StringRef rhs)
{
	int cmp = memcmp(lhs.data, rhs.data, std::min(lhs.size, rhs.size));
	if (cmp == 0)
		return lhs.size < rhs.size;
	else
		return cmp < 0;
}


struct StringRefHash
{
	size_t operator() (StringRef x) const
	{
		return CityHash64(x.data, x.size);
	}
};


namespace std
{
	template <>
	struct hash<StringRef> : public StringRefHash {};
}


namespace ZeroTraits
{
	inline bool check(StringRef x) { return nullptr == x.data; }
	inline void set(StringRef & x) { x.data = nullptr; }
};


inline bool operator==(StringRef lhs, const char * rhs)
{
	for (size_t pos = 0; pos < lhs.size; ++pos)
		if (!rhs[pos] || lhs.data[pos] != rhs[pos])
			return false;

	return true;
}

inline std::ostream & operator<<(std::ostream & os, const StringRef & str)
{
	if (str.data)
		os.write(str.data, str.size);

	return os;
}