ClickHouse/dbms/Functions/FunctionsRandom.h
Ivan 97f2a2213e
Move all folders inside /dbms one level up (#9974)
* Move some code outside dbms/src folder
* Fix paths
2020-04-02 02:51:21 +03:00

87 lines
2.8 KiB
C++

#pragma once
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnVector.h>
#include <Functions/IFunctionImpl.h>
#include <IO/WriteHelpers.h>
namespace DB
{
namespace ErrorCodes
{
extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
}
/** 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.
*
* Example:
* SELECT rand(), rand() - will output two identical columns.
* SELECT rand(1), rand(2) - will output two different columns.
*
* Non-cryptographic generators:
*
* rand - linear congruential generator 0 .. 2^32 - 1.
* rand64 - combines several rand values to get values from the range 0 .. 2^64 - 1.
*
* randConstant - service function, produces a constant column with a random value.
*
* The time is used as the seed.
* Note: it is reinitialized for each block.
* This means that the timer must be of sufficient resolution to give different values to each block.
*/
struct RandImpl
{
/// Fill memory with random data. The memory region must be 15-bytes padded.
static void execute(char * output, size_t size);
};
template <typename ToType, typename Name>
class FunctionRandom : public IFunction
{
public:
static constexpr auto name = Name::name;
static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandom>(); }
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>>();
}
void executeImpl(Block & block, const ColumnNumbers &, size_t result, size_t input_rows_count) override
{
auto col_to = ColumnVector<ToType>::create();
typename ColumnVector<ToType>::Container & vec_to = col_to->getData();
size_t size = input_rows_count;
vec_to.resize(size);
RandImpl::execute(reinterpret_cast<char *>(vec_to.data()), vec_to.size() * sizeof(ToType));
block.getByPosition(result).column = std::move(col_to);
}
};
}