mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-12-15 10:52:30 +00:00
41 lines
1.7 KiB
C++
41 lines
1.7 KiB
C++
#pragma once
|
|
|
|
#include <Columns/IColumn.h>
|
|
|
|
|
|
namespace DB
|
|
{
|
|
|
|
/** Allows to access internal array of ColumnVector or ColumnFixedString without cast to concrete type.
|
|
* We will inherit ColumnVector and ColumnFixedString from this class instead of IColumn.
|
|
* Assumes data layout of ColumnVector, ColumnFixedString and PODArray.
|
|
*
|
|
* Why it is needed?
|
|
*
|
|
* There are some algorithms that specialize on the size of data type but doesn't care about concrete type.
|
|
* The same specialization may work for UInt64, Int64, Float64, FixedString(8), if it only does byte moving and hashing.
|
|
* To avoid code bloat and compile time increase, we can use single template instantiation for these cases
|
|
* and just static_cast pointer to some single column type (e. g. ColumnUInt64) assuming that all types have identical memory layout.
|
|
*
|
|
* But this static_cast (downcast to unrelated type) is illegal according to the C++ standard and UBSan warns about it.
|
|
* To allow functional tests to work under UBSan we have to separate some base class that will present the memory layout in explicit way,
|
|
* and we will do static_cast to this class.
|
|
*/
|
|
class ColumnVectorHelper : public IColumn
|
|
{
|
|
public:
|
|
template <size_t ELEMENT_SIZE>
|
|
const char * getRawDataBegin() const
|
|
{
|
|
return reinterpret_cast<const PODArrayBase<ELEMENT_SIZE, 4096, Allocator<false>, 15, 16> *>(reinterpret_cast<const char *>(this) + sizeof(*this))->raw_data();
|
|
}
|
|
|
|
template <size_t ELEMENT_SIZE>
|
|
void insertRawData(const char * ptr)
|
|
{
|
|
return reinterpret_cast<PODArrayBase<ELEMENT_SIZE, 4096, Allocator<false>, 15, 16> *>(reinterpret_cast<char *>(this) + sizeof(*this))->push_back_raw(ptr);
|
|
}
|
|
};
|
|
|
|
}
|