ClickHouse/dbms/include/DB/IO/HashingWriteBuffer.h

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#pragma once
#include <DB/IO/WriteBuffer.h>
#include <DB/IO/BufferWithOwnMemory.h>
#include <DB/IO/ReadHelpers.h>
#define DBMS_DEFAULT_HASHING_BLOCK_SIZE 2048ULL
namespace DB
{
template <class Buffer>
class IHashingBuffer : public BufferWithOwnMemory<Buffer>
{
public:
IHashingBuffer<Buffer>(size_t block_size_ = DBMS_DEFAULT_HASHING_BLOCK_SIZE)
: BufferWithOwnMemory<Buffer>(block_size_), block_pos(0), block_size(block_size_), state(0, 0)
{
}
uint128 getHash()
{
if (block_pos)
return CityHash128WithSeed(&BufferWithOwnMemory<Buffer>::memory[0], block_pos, state);
else
return state;
}
void append(DB::BufferBase::Position data)
{
state = CityHash128WithSeed(data, block_size, state);
}
/// вычисление хэша зависит от разбиения по блокам
/// поэтому нужно вычислить хэш от n полных кусочков и одного неполного
void calculateHash(DB::BufferBase::Position data, size_t len);
protected:
size_t block_pos;
size_t block_size;
uint128 state;
};
/** Вычисляет хеш от записываемых данных и передает их в указанный WriteBuffer.
* В качестве основного буфера используется буфер вложенного WriteBuffer.
*/
class HashingWriteBuffer : public IHashingBuffer<WriteBuffer>
{
private:
WriteBuffer & out;
void nextImpl() override
{
size_t len = offset();
Position data = working_buffer.begin();
calculateHash(data, len);
out.position() = pos;
out.next();
working_buffer = out.buffer();
}
public:
HashingWriteBuffer(
WriteBuffer & out_,
size_t block_size_ = DBMS_DEFAULT_HASHING_BLOCK_SIZE)
: IHashingBuffer<DB::WriteBuffer>(block_size_), out(out_)
{
out.next(); /// Если до нас в out что-то уже писали, не дадим остаткам этих данных повлиять на хеш.
working_buffer = out.buffer();
pos = working_buffer.begin();
state = uint128(0, 0);
}
uint128 getHash()
{
next();
return IHashingBuffer<WriteBuffer>::getHash();
}
};
}
std::string uint128ToString(uint128 data);
std::ostream & operator<<(std::ostream & os, const uint128 & data);
std::istream & operator>>(std::istream & is, uint128 & data);