ClickHouse/dbms/IO/HashingReadBuffer.h

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#pragma once
#include <IO/ReadBuffer.h>
#include <IO/HashingWriteBuffer.h>
namespace DB
{
/*
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* 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:
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();
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/// calculate hash from the data already read
if (working_buffer.size())
{
calculateHash(pos, working_buffer.end() - pos);
}
}
private:
bool nextImpl() override
{
in.position() = pos;
bool res = in.next();
working_buffer = in.buffer();
pos = in.position();
calculateHash(working_buffer.begin(), working_buffer.size());
return res;
}
private:
ReadBuffer & in;
};
}