1 | #pragma once |
2 | |
3 | #include <DataTypes/DataTypesNumber.h> |
4 | #include <Columns/ColumnVector.h> |
5 | #include <Functions/IFunctionImpl.h> |
6 | #include <IO/WriteHelpers.h> |
7 | |
8 | |
9 | namespace DB |
10 | { |
11 | |
12 | namespace ErrorCodes |
13 | { |
14 | extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH; |
15 | } |
16 | |
17 | /** Pseudo-random number generation functions. |
18 | * The function can be called without arguments or with one argument. |
19 | * The argument is ignored and only serves to ensure that several calls to one function are considered different and do not stick together. |
20 | * |
21 | * Example: |
22 | * SELECT rand(), rand() - will output two identical columns. |
23 | * SELECT rand(1), rand(2) - will output two different columns. |
24 | * |
25 | * Non-cryptographic generators: |
26 | * |
27 | * rand - linear congruential generator 0 .. 2^32 - 1. |
28 | * rand64 - combines several rand values to get values from the range 0 .. 2^64 - 1. |
29 | * |
30 | * randConstant - service function, produces a constant column with a random value. |
31 | * |
32 | * The time is used as the seed. |
33 | * Note: it is reinitialized for each block. |
34 | * This means that the timer must be of sufficient resolution to give different values to each block. |
35 | */ |
36 | |
37 | struct RandImpl |
38 | { |
39 | /// Fill memory with random data. The memory region must be 15-bytes padded. |
40 | static void execute(char * output, size_t size); |
41 | }; |
42 | |
43 | |
44 | template <typename ToType, typename Name> |
45 | class FunctionRandom : public IFunction |
46 | { |
47 | public: |
48 | static constexpr auto name = Name::name; |
49 | static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandom>(); } |
50 | |
51 | String getName() const override |
52 | { |
53 | return name; |
54 | } |
55 | |
56 | bool isDeterministic() const override { return false; } |
57 | bool isDeterministicInScopeOfQuery() const override { return false; } |
58 | bool useDefaultImplementationForNulls() const override { return false; } |
59 | |
60 | bool isVariadic() const override { return true; } |
61 | size_t getNumberOfArguments() const override { return 0; } |
62 | |
63 | DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override |
64 | { |
65 | if (arguments.size() > 1) |
66 | throw Exception("Number of arguments for function " + getName() + " doesn't match: passed " |
67 | + toString(arguments.size()) + ", should be 0 or 1." , |
68 | ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH); |
69 | |
70 | return std::make_shared<DataTypeNumber<ToType>>(); |
71 | } |
72 | |
73 | void executeImpl(Block & block, const ColumnNumbers &, size_t result, size_t input_rows_count) override |
74 | { |
75 | auto col_to = ColumnVector<ToType>::create(); |
76 | typename ColumnVector<ToType>::Container & vec_to = col_to->getData(); |
77 | |
78 | size_t size = input_rows_count; |
79 | vec_to.resize(size); |
80 | RandImpl::execute(reinterpret_cast<char *>(vec_to.data()), vec_to.size() * sizeof(ToType)); |
81 | |
82 | block.getByPosition(result).column = std::move(col_to); |
83 | } |
84 | }; |
85 | |
86 | } |
87 | |