ClickHouse/src/Functions/jumpConsistentHash.cpp
2020-09-08 03:59:13 +03:00

48 lines
1.1 KiB
C++

#include "FunctionsConsistentHashing.h"
#include <Functions/FunctionFactory.h>
namespace DB
{
namespace
{
/// Code from https://arxiv.org/pdf/1406.2294.pdf
inline int32_t JumpConsistentHash(uint64_t key, int32_t num_buckets)
{
int64_t b = -1, j = 0;
while (j < num_buckets)
{
b = j;
key = key * 2862933555777941757ULL + 1;
j = static_cast<int64_t>((b + 1) * (double(1LL << 31) / double((key >> 33) + 1)));
}
return static_cast<int32_t>(b);
}
struct JumpConsistentHashImpl
{
static constexpr auto name = "jumpConsistentHash";
using HashType = UInt64;
using ResultType = Int32;
using BucketsType = ResultType;
static constexpr auto max_buckets = static_cast<UInt64>(std::numeric_limits<BucketsType>::max());
static inline ResultType apply(UInt64 hash, BucketsType n)
{
return JumpConsistentHash(hash, n);
}
};
using FunctionJumpConsistentHash = FunctionConsistentHashImpl<JumpConsistentHashImpl>;
}
void registerFunctionJumpConsistentHash(FunctionFactory & factory)
{
factory.registerFunction<FunctionJumpConsistentHash>();
}
}