ClickHouse/src/Functions/FunctionsRandom.h

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#pragma once
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnVector.h>
#include <Functions/IFunctionImpl.h>
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#include <Functions/TargetSpecific.h>
#include <Functions/PerformanceAdaptors.h>
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#include <IO/WriteHelpers.h>
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namespace DB
{
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namespace ErrorCodes
{
extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
}
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/** Pseudo-random number generation functions.
* The function can be called without arguments or with one argument.
* The argument is ignored and only serves to ensure that several calls to one function are considered different and do not stick together.
*
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* Example:
* SELECT rand(), rand() - will output two identical columns.
* SELECT rand(1), rand(2) - will output two different columns.
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*
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* Non-cryptographic generators:
*
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* rand - linear congruential generator 0 .. 2^32 - 1.
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* rand64 - combines several rand values to get values from the range 0 .. 2^64 - 1.
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*
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* randConstant - service function, produces a constant column with a random value.
*
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* The time is used as the seed.
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* Note: it is reinitialized for each columns.
* This means that the timer must be of sufficient resolution to give different values to each columns.
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*/
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DECLARE_MULTITARGET_CODE(
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struct RandImpl
{
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/// Fill memory with random data. The memory region must be 15-bytes padded.
static void execute(char * output, size_t size);
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};
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) // DECLARE_MULTITARGET_CODE
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template <typename RandImpl, typename ToType, typename Name>
class FunctionRandomImpl : public IFunction
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{
public:
static constexpr auto name = Name::name;
String getName() const override
{
return name;
}
bool isDeterministic() const override { return false; }
bool isDeterministicInScopeOfQuery() const override { return false; }
bool useDefaultImplementationForNulls() const override { return false; }
bool isVariadic() const override { return true; }
size_t getNumberOfArguments() const override { return 0; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
if (arguments.size() > 1)
throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
+ toString(arguments.size()) + ", should be 0 or 1.",
ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
return std::make_shared<DataTypeNumber<ToType>>();
}
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ColumnPtr executeImpl(ColumnsWithTypeAndName &, const DataTypePtr &, size_t input_rows_count) const override
{
auto col_to = ColumnVector<ToType>::create();
typename ColumnVector<ToType>::Container & vec_to = col_to->getData();
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size_t size = input_rows_count;
vec_to.resize(size);
RandImpl::execute(reinterpret_cast<char *>(vec_to.data()), vec_to.size() * sizeof(ToType));
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return col_to;
}
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};
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template <typename ToType, typename Name>
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class FunctionRandom : public FunctionRandomImpl<TargetSpecific::Default::RandImpl, ToType, Name>
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{
public:
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explicit FunctionRandom(const Context & context) : selector(context)
{
selector.registerImplementation<TargetArch::Default,
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FunctionRandomImpl<TargetSpecific::Default::RandImpl, ToType, Name>>();
#if USE_MULTITARGET_CODE
selector.registerImplementation<TargetArch::AVX2,
FunctionRandomImpl<TargetSpecific::AVX2::RandImpl, ToType, Name>>();
#endif
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}
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ColumnPtr executeImpl(ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
{
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return selector.selectAndExecute(arguments, result_type, input_rows_count);
}
static FunctionPtr create(const Context & context)
{
return std::make_shared<FunctionRandom<ToType, Name>>(context);
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}
private:
ImplementationSelector<IFunction> selector;
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};
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}