mirror of
https://github.com/ClickHouse/ClickHouse.git
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301 lines
8.8 KiB
C++
301 lines
8.8 KiB
C++
#pragma once
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#include <Core/Types.h>
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#include <Common/UInt128.h>
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#include <common/unaligned.h>
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#include <type_traits>
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/** Hash functions that are better than the trivial function std::hash.
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*
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* Example: when we do aggregation by the visitor ID, the performance increase is more than 5 times.
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* This is because of following reasons:
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* - in Yandex, visitor identifier is an integer that has timestamp with seconds resolution in lower bits;
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* - in typical implementation of standard library, hash function for integers is trivial and just use lower bits;
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* - traffic is non-uniformly distributed across a day;
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* - we are using open-addressing linear probing hash tables that are most critical to hash function quality,
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* and trivial hash function gives disastrous results.
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*/
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/** Taken from MurmurHash. This is Murmur finalizer.
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* Faster than intHash32 when inserting into the hash table UInt64 -> UInt64, where the key is the visitor ID.
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*/
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inline DB::UInt64 intHash64(DB::UInt64 x)
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{
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x ^= x >> 33;
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x *= 0xff51afd7ed558ccdULL;
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x ^= x >> 33;
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x *= 0xc4ceb9fe1a85ec53ULL;
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x ^= x >> 33;
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return x;
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}
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/** CRC32C is not very high-quality as a hash function,
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* according to avalanche and bit independence tests (see SMHasher software), as well as a small number of bits,
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* but can behave well when used in hash tables,
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* due to high speed (latency 3 + 1 clock cycle, throughput 1 clock cycle).
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* Works only with SSE 4.2 support.
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*/
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#ifdef __SSE4_2__
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#include <nmmintrin.h>
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#endif
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#if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32)
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#include <arm_acle.h>
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#include <arm_neon.h>
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#endif
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inline DB::UInt64 intHashCRC32(DB::UInt64 x)
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{
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#ifdef __SSE4_2__
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return _mm_crc32_u64(-1ULL, x);
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#elif defined(__aarch64__) && defined(__ARM_FEATURE_CRC32)
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return __crc32cd(-1U, x);
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#else
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/// On other platforms we do not have CRC32. NOTE This can be confusing.
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return intHash64(x);
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#endif
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}
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inline DB::UInt64 intHashCRC32(DB::UInt64 x, DB::UInt64 updated_value)
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{
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#ifdef __SSE4_2__
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return _mm_crc32_u64(updated_value, x);
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#elif defined(__aarch64__) && defined(__ARM_FEATURE_CRC32)
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return __crc32cd(updated_value, x);
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#else
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/// On other platforms we do not have CRC32. NOTE This can be confusing.
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return intHash64(x) ^ updated_value;
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#endif
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}
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template <typename T>
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inline typename std::enable_if<(sizeof(T) > sizeof(DB::UInt64)), DB::UInt64>::type
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intHashCRC32(const T & x, DB::UInt64 updated_value)
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{
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auto * begin = reinterpret_cast<const char *>(&x);
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for (size_t i = 0; i < sizeof(T); i += sizeof(UInt64))
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{
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updated_value = intHashCRC32(unalignedLoad<DB::UInt64>(begin), updated_value);
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begin += sizeof(DB::UInt64);
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}
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return updated_value;
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}
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inline UInt32 updateWeakHash32(const DB::UInt8 * pos, size_t size, DB::UInt32 updated_value)
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{
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if (size < 8)
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{
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DB::UInt64 value = 0;
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auto * value_ptr = reinterpret_cast<unsigned char *>(&value);
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typedef __attribute__((__aligned__(1))) uint16_t uint16_unaligned_t;
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typedef __attribute__((__aligned__(1))) uint32_t uint32_unaligned_t;
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/// Adopted code from FastMemcpy.h (memcpy_tiny)
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switch (size)
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{
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case 0:
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break;
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case 1:
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value_ptr[0] = pos[0];
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break;
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case 2:
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*reinterpret_cast<uint16_t *>(value_ptr) = *reinterpret_cast<const uint16_unaligned_t *>(pos);
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break;
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case 3:
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*reinterpret_cast<uint16_t *>(value_ptr) = *reinterpret_cast<const uint16_unaligned_t *>(pos);
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value_ptr[2] = pos[2];
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break;
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case 4:
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*reinterpret_cast<uint32_t *>(value_ptr) = *reinterpret_cast<const uint32_unaligned_t *>(pos);
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break;
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case 5:
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*reinterpret_cast<uint32_t *>(value_ptr) = *reinterpret_cast<const uint32_unaligned_t *>(pos);
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value_ptr[4] = pos[4];
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break;
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case 6:
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*reinterpret_cast<uint32_t *>(value_ptr) = *reinterpret_cast<const uint32_unaligned_t *>(pos);
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*reinterpret_cast<uint16_unaligned_t *>(value_ptr + 4) =
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*reinterpret_cast<const uint16_unaligned_t *>(pos + 4);
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break;
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case 7:
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*reinterpret_cast<uint32_t *>(value_ptr) = *reinterpret_cast<const uint32_unaligned_t *>(pos);
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*reinterpret_cast<uint32_unaligned_t *>(value_ptr + 3) =
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*reinterpret_cast<const uint32_unaligned_t *>(pos + 3);
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break;
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default:
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__builtin_unreachable();
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}
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value_ptr[7] = size;
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return intHashCRC32(value, updated_value);
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}
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const auto * end = pos + size;
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while (pos + 8 <= end)
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{
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auto word = unalignedLoad<UInt64>(pos);
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updated_value = intHashCRC32(word, updated_value);
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pos += 8;
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}
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if (pos < end)
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{
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/// If string size is not divisible by 8.
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/// Lets' assume the string was 'abcdefghXYZ', so it's tail is 'XYZ'.
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DB::UInt8 tail_size = end - pos;
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/// Load tailing 8 bytes. Word is 'defghXYZ'.
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auto word = unalignedLoad<UInt64>(end - 8);
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/// Prepare mask which will set other 5 bytes to 0. It is 0xFFFFFFFFFFFFFFFF << 5 = 0xFFFFFF0000000000.
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/// word & mask = '\0\0\0\0\0XYZ' (bytes are reversed because of little ending)
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word &= (~UInt64(0)) << DB::UInt8(8 * (8 - tail_size));
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/// Use least byte to store tail length.
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word |= tail_size;
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/// Now word is '\3\0\0\0\0XYZ'
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updated_value = intHashCRC32(word, updated_value);
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}
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return updated_value;
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}
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template <typename T>
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inline size_t DefaultHash64(T key)
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{
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union
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{
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T in;
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DB::UInt64 out;
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} u;
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u.out = 0;
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u.in = key;
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return intHash64(u.out);
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}
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template <typename T, typename Enable = void>
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struct DefaultHash;
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template <typename T>
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struct DefaultHash<T, std::enable_if_t<is_arithmetic_v<T>>>
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{
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size_t operator() (T key) const
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{
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return DefaultHash64<T>(key);
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}
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};
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template <typename T>
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struct DefaultHash<T, std::enable_if_t<DB::IsDecimalNumber<T> && sizeof(T) <= 8>>
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{
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size_t operator() (T key) const
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{
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return DefaultHash64<typename T::NativeType>(key);
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}
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};
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template <typename T>
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struct DefaultHash<T, std::enable_if_t<DB::IsDecimalNumber<T> && sizeof(T) == 16>>
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{
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size_t operator() (T key) const
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{
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return DefaultHash64<Int64>(key >> 64) ^ DefaultHash64<Int64>(key);
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}
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};
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template <typename T> struct HashCRC32;
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template <typename T>
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inline size_t hashCRC32(T key)
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{
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union
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{
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T in;
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DB::UInt64 out;
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} u;
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u.out = 0;
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u.in = key;
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return intHashCRC32(u.out);
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}
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#define DEFINE_HASH(T) \
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template <> struct HashCRC32<T>\
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{\
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size_t operator() (T key) const\
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{\
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return hashCRC32<T>(key);\
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}\
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};
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DEFINE_HASH(DB::UInt8)
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DEFINE_HASH(DB::UInt16)
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DEFINE_HASH(DB::UInt32)
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DEFINE_HASH(DB::UInt64)
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DEFINE_HASH(DB::UInt128)
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DEFINE_HASH(DB::Int8)
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DEFINE_HASH(DB::Int16)
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DEFINE_HASH(DB::Int32)
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DEFINE_HASH(DB::Int64)
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DEFINE_HASH(DB::Float32)
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DEFINE_HASH(DB::Float64)
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#undef DEFINE_HASH
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/// It is reasonable to use for UInt8, UInt16 with sufficient hash table size.
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struct TrivialHash
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{
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template <typename T>
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size_t operator() (T key) const
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{
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return key;
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}
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};
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/** A relatively good non-cryptographic hash function from UInt64 to UInt32.
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* But worse (both in quality and speed) than just cutting intHash64.
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* Taken from here: http://www.concentric.net/~ttwang/tech/inthash.htm
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*
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* Slightly changed compared to the function by link: shifts to the right are accidentally replaced by a cyclic shift to the right.
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* This change did not affect the smhasher test results.
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*
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* It is recommended to use different salt for different tasks.
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* That was the case that in the database values were sorted by hash (for low-quality pseudo-random spread),
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* and in another place, in the aggregate function, the same hash was used in the hash table,
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* as a result, this aggregate function was monstrously slowed due to collisions.
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*
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* NOTE Salting is far from perfect, because it commutes with first steps of calculation.
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*
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* NOTE As mentioned, this function is slower than intHash64.
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* But occasionally, it is faster, when written in a loop and loop is vectorized.
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*/
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template <DB::UInt64 salt>
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inline DB::UInt32 intHash32(DB::UInt64 key)
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{
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key ^= salt;
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key = (~key) + (key << 18);
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key = key ^ ((key >> 31) | (key << 33));
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key = key * 21;
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key = key ^ ((key >> 11) | (key << 53));
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key = key + (key << 6);
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key = key ^ ((key >> 22) | (key << 42));
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return key;
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}
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/// For containers.
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template <typename T, DB::UInt64 salt = 0>
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struct IntHash32
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{
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size_t operator() (const T & key) const
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{
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return intHash32<salt>(key);
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}
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};
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