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