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#pragma once
#include <IO/HashingWriteBuffer.h>
#include <IO/ReadBuffer.h>
namespace DB
{
/*
* Calculates the hash from the read data. When reading, the data is read from the nested ReadBuffer.
* Small pieces are copied into its own memory.
*/
class HashingReadBuffer : public IHashingBuffer<ReadBuffer>
{
public:
explicit HashingReadBuffer(ReadBuffer & in_, size_t block_size_ = DBMS_DEFAULT_HASHING_BLOCK_SIZE)
: IHashingBuffer<ReadBuffer>(block_size_), in(in_)
{
working_buffer = in.buffer();
pos = in.position();
hashing_begin = pos;
}
uint128 getHash()
{
if (pos > hashing_begin)
{
calculateHash(hashing_begin, pos - hashing_begin);
hashing_begin = pos;
}
return IHashingBuffer<ReadBuffer>::getHash();
}
private:
bool nextImpl() override
{
if (pos > hashing_begin)
calculateHash(hashing_begin, pos - hashing_begin);
in.position() = pos;
bool res = in.next();
working_buffer = in.buffer();
// `pos` may be different from working_buffer.begin() when using sophisticated ReadBuffers.
pos = in.position();
hashing_begin = pos;
return res;
}
ReadBuffer & in;
BufferBase::Position hashing_begin;
};
}
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