ClickHouse/dbms/src/Functions/FunctionsRandom.h

224 lines
6.8 KiB
C++

#pragma once
#include <DataTypes/DataTypesNumber.h>
#include <Columns/ColumnVector.h>
#include <Columns/ColumnConst.h>
#include <Functions/IFunction.h>
#include <Functions/FunctionHelpers.h>
#include <IO/WriteHelpers.h>
#include <Common/HashTable/Hash.h>
#include <Common/randomSeed.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 congruental 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.
*/
namespace detail
{
/// NOTE Probably
/// http://www.pcg-random.org/
/// or http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/
/// or http://docs.yeppp.info/c/group__yep_random___w_e_l_l1024a.html
/// could go better.
struct LinearCongruentialGenerator
{
/// Constants from `man lrand48_r`.
static constexpr UInt64 a = 0x5DEECE66D;
static constexpr UInt64 c = 0xB;
/// And this is from `head -c8 /dev/urandom | xxd -p`
UInt64 current = 0x09826f4a081cee35ULL;
LinearCongruentialGenerator() {}
LinearCongruentialGenerator(UInt64 value) : current(value) {}
void seed(UInt64 value)
{
current = value;
}
UInt32 next()
{
current = current * a + c;
return current >> 16;
}
};
void seed(LinearCongruentialGenerator & generator, intptr_t additional_seed);
}
struct RandImpl
{
using ReturnType = UInt32;
static void execute(ReturnType * output, size_t size)
{
detail::LinearCongruentialGenerator generator0;
detail::LinearCongruentialGenerator generator1;
detail::LinearCongruentialGenerator generator2;
detail::LinearCongruentialGenerator generator3;
detail::seed(generator0, 0xfb4121280b2ab902ULL + reinterpret_cast<intptr_t>(output));
detail::seed(generator1, 0x0121cf76df39c673ULL + reinterpret_cast<intptr_t>(output));
detail::seed(generator2, 0x17ae86e3a19a602fULL + reinterpret_cast<intptr_t>(output));
detail::seed(generator3, 0x8b6e16da7e06d622ULL + reinterpret_cast<intptr_t>(output));
ReturnType * pos = output;
ReturnType * end = pos + size;
ReturnType * end4 = pos + size / 4 * 4;
while (pos < end4)
{
pos[0] = generator0.next();
pos[1] = generator1.next();
pos[2] = generator2.next();
pos[3] = generator3.next();
pos += 4;
}
while (pos < end)
{
pos[0] = generator0.next();
++pos;
}
}
};
struct Rand64Impl
{
using ReturnType = UInt64;
static void execute(ReturnType * output, size_t size)
{
RandImpl::execute(reinterpret_cast<RandImpl::ReturnType *>(output), size * 2);
}
};
template <typename Impl, typename Name>
class FunctionRandom : public IFunction
{
private:
using ToType = typename Impl::ReturnType;
public:
static constexpr auto name = Name::name;
static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandom>(); }
String getName() const override
{
return name;
}
bool isVariadic() const override { return true; }
size_t getNumberOfArguments() const override { return 0; }
bool isDeterministicInScopeOfQuery() override { return false; }
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<typename Impl::ReturnType>>();
}
void executeImpl(Block & block, const ColumnNumbers & /*arguments*/, size_t result) override
{
auto col_to = ColumnVector<ToType>::create();
typename ColumnVector<ToType>::Container & vec_to = col_to->getData();
size_t size = block.rows();
vec_to.resize(size);
Impl::execute(&vec_to[0], vec_to.size());
block.getByPosition(result).column = std::move(col_to);
}
};
template <typename Impl, typename Name>
class FunctionRandomConstant : public IFunction
{
private:
using ToType = typename Impl::ReturnType;
/// The value is one for different blocks.
bool is_initialized = false;
ToType value;
public:
static constexpr auto name = Name::name;
static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandomConstant>(); }
String getName() const override
{
return name;
}
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<typename Impl::ReturnType>>();
}
void executeImpl(Block & block, const ColumnNumbers & /*arguments*/, size_t result) override
{
if (!is_initialized)
{
is_initialized = true;
typename ColumnVector<ToType>::Container vec_to(1);
Impl::execute(&vec_to[0], vec_to.size());
value = vec_to[0];
}
block.getByPosition(result).column = DataTypeNumber<ToType>().createColumnConst(block.rows(), toField(value));
}
};
struct NameRand { static constexpr auto name = "rand"; };
struct NameRand64 { static constexpr auto name = "rand64"; };
struct NameRandConstant { static constexpr auto name = "randConstant"; };
using FunctionRand = FunctionRandom<RandImpl, NameRand> ;
using FunctionRand64 = FunctionRandom<Rand64Impl, NameRand64>;
using FunctionRandConstant = FunctionRandomConstant<RandImpl, NameRandConstant>;
}