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

#pragma once

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

#include <string>
#include <vector>

#include <functional>
#include <ostream>

#if defined(__x86_64__)
	#include <emmintrin.h>
#endif


/// 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() = default;

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

	explicit operator std::string() const { return toString(); }
};

using StringRefs = std::vector<StringRef>;


#if defined(__x86_64__)

/** Сравнение строк на равенство.
  * Подход является спорным и выигрывает не во всех случаях.
  * Подробнее смотрите hash_map_string_2.cpp
  */

inline bool compareSSE2(const char * p1, const char * p2)
{
	return 0xFFFF == _mm_movemask_epi8(_mm_cmpeq_epi8(
		_mm_loadu_si128(reinterpret_cast<const __m128i *>(p1)),
		_mm_loadu_si128(reinterpret_cast<const __m128i *>(p2))));
}

inline bool compareSSE2x4(const char * p1, const char * p2)
{
	return 0xFFFF == _mm_movemask_epi8(
		_mm_and_si128(
			_mm_and_si128(
				_mm_cmpeq_epi8(
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p1)),
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p2))),
				_mm_cmpeq_epi8(
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p1) + 1),
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p2) + 1))),
			_mm_and_si128(
				_mm_cmpeq_epi8(
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p1) + 2),
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p2) + 2)),
				_mm_cmpeq_epi8(
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p1) + 3),
					_mm_loadu_si128(reinterpret_cast<const __m128i *>(p2) + 3)))));
}

inline bool memequalSSE2Wide(const char * p1, const char * p2, size_t size)
{
	while (size >= 64)
	{
		if (compareSSE2x4(p1, p2))
		{
			p1 += 64;
			p2 += 64;
			size -= 64;
		}
		else
			return false;
	}

	switch ((size % 64) / 16)
	{
		case 3: if (!compareSSE2(p1 + 32, p2 + 32)) return false;
		case 2: if (!compareSSE2(p1 + 16, p2 + 16)) return false;
		case 1: if (!compareSSE2(p1     , p2     )) return false;
		case 0: break;
	}

	p1 += (size % 64) / 16 * 16;
	p2 += (size % 64) / 16 * 16;

	switch (size % 16)
	{
		case 15: if (p1[14] != p2[14]) return false;
		case 14: if (p1[13] != p2[13]) return false;
		case 13: if (p1[12] != p2[12]) return false;
		case 12: if (reinterpret_cast<const uint32_t *>(p1)[2] == reinterpret_cast<const uint32_t *>(p2)[2]) goto l8; else return false;
		case 11: if (p1[10] != p2[10]) return false;
		case 10: if (p1[9] != p2[9]) return false;
		case 9:  if (p1[8] != p2[8]) return false;
	l8: case 8:  return reinterpret_cast<const uint64_t *>(p1)[0] == reinterpret_cast<const uint64_t *>(p2)[0];
		case 7:  if (p1[6] != p2[6]) return false;
		case 6:  if (p1[5] != p2[5]) return false;
		case 5:  if (p1[4] != p2[4]) return false;
		case 4:  return reinterpret_cast<const uint32_t *>(p1)[0] == reinterpret_cast<const uint32_t *>(p2)[0];
		case 3:  if (p1[2] != p2[2]) return false;
		case 2:  return reinterpret_cast<const uint16_t *>(p1)[0] == reinterpret_cast<const uint16_t *>(p2)[0];
		case 1:  if (p1[0] != p2[0]) return false;
		case 0:  break;
	}

	return true;
}

#endif


inline bool operator== (StringRef lhs, StringRef rhs)
{
	if (lhs.size != rhs.size)
		return false;

	if (lhs.size == 0)
		return true;

#if defined(__x86_64__)
	return memequalSSE2Wide(lhs.data, rhs.data, lhs.size);
#else
	return 0 == memcmp(lhs.data, rhs.data, lhs.size);
#endif
}

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));
	return cmp < 0 || (cmp == 0 && lhs.size < rhs.size);
}

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


/** Хэш-функции.
  * Можно использовать либо CityHash64,
  *  либо функцию на основе инструкции crc32,
  *  которая является заведомо менее качественной, но на реальных наборах данных,
  *  при использовании в хэш-таблице, работает существенно быстрее.
  * Подробнее см. hash_map_string_3.cpp
  */

#if defined(__x86_64__)

#ifdef __SSE4_1__
#include <smmintrin.h>
#else

inline uint64 _mm_crc32_u64(uint64 crc, uint64 value)
{
	asm("crc32q %[value], %[crc]\n" : [crc] "+r" (crc) : [value] "rm" (value));
	return crc;
}

#endif

/// Кусочки взяты из CityHash.

inline uint64 hashLen16(uint64 u, uint64 v)
{
	return Hash128to64(uint128(u, v));
}

inline uint64 shiftMix(uint64 val)
{
	return val ^ (val >> 47);
}

inline uint64 rotateByAtLeast1(uint64 val, int shift)
{
	return (val >> shift) | (val << (64 - shift));
}

inline size_t hashLessThan8(const char * data, size_t size)
{
	static constexpr uint64 k2 = 0x9ae16a3b2f90404fULL;
	static constexpr uint64 k3 = 0xc949d7c7509e6557ULL;

	if (size >= 4)
	{
		uint64 a = *reinterpret_cast<const uint32_t *>(data);;
		return hashLen16(size + (a << 3), *reinterpret_cast<const uint32_t *>(data + size - 4));
	}

	if (size > 0)
	{
		uint8 a = data[0];
		uint8 b = data[size >> 1];
		uint8 c = data[size - 1];
		uint32 y = static_cast<uint32>(a) + (static_cast<uint32>(b) << 8);
		uint32 z = size + (static_cast<uint32>(c) << 2);
		return shiftMix(y * k2 ^ z * k3) * k2;
	}

	return k2;
}

inline size_t hashLessThan16(const char * data, size_t size)
{
	if (size > 8)
	{
		uint64 a = *reinterpret_cast<const uint64_t *>(data);
		uint64 b = *reinterpret_cast<const uint64_t *>(data + size - 8);
		return hashLen16(a, rotateByAtLeast1(b + size, size)) ^ b;
	}

	return hashLessThan8(data, size);
}

struct CRC32Hash
{
	size_t operator() (StringRef x) const
	{
		const char * pos = x.data;
		size_t size = x.size;

		if (size == 0)
			return 0;

		if (size < 8)
		{
			return hashLessThan8(x.data, x.size);
		}

		const char * end = pos + size;
		size_t res = -1ULL;

		do
		{
			uint64_t word = *reinterpret_cast<const uint64_t *>(pos);
			res = _mm_crc32_u64(res, word);

			pos += 8;
		} while (pos + 8 < end);

		uint64_t word = *reinterpret_cast<const uint64_t *>(end - 8);	/// Не уверен, что это нормально.
		res = _mm_crc32_u64(res, word);

		return res;
	}
};

struct StringRefHash : CRC32Hash {};

#else

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

#endif


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


namespace ZeroTraits
{
	inline bool check(StringRef x) { return 0 == x.size; }
	inline void set(StringRef & x) { x.size = 0; }
};


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;
}