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114 lines
4.2 KiB
C++
114 lines
4.2 KiB
C++
#include <Functions/IFunctionImpl.h>
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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionHelpers.h>
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#include <Columns/ColumnString.h>
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#include <DataTypes/DataTypeString.h>
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#include <Common/thread_local_rng.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
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extern const int ILLEGAL_TYPE_OF_ARGUMENT;
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extern const int TOO_LARGE_STRING_SIZE;
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}
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/** Generate random string of specified length with printable ASCII characters, almost uniformly distributed.
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* First argument is length, other optional arguments are ignored and used to prevent common subexpression elimination to get different values.
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*/
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class FunctionRandomPrintableASCII : public IFunction
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{
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public:
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static constexpr auto name = "randomPrintableASCII";
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static FunctionPtr create(const Context &) { return std::make_shared<FunctionRandomPrintableASCII>(); }
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String getName() const override
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{
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return name;
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}
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bool isVariadic() const override { return true; }
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size_t getNumberOfArguments() const override { return 0; }
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DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
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{
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if (arguments.empty())
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throw Exception("Function " + getName() + " requires at least one argument: the size of resulting string",
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ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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if (arguments.size() > 2)
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throw Exception("Function " + getName() + " requires at most two arguments: the size of resulting string and optional disambiguation tag",
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ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
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const IDataType & length_type = *arguments[0];
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if (!isNumber(length_type))
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throw Exception("First argument of function " + getName() + " must have numeric type", ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
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return std::make_shared<DataTypeString>();
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}
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bool isDeterministic() const override { return false; }
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bool isDeterministicInScopeOfQuery() const override { return false; }
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void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
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{
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auto col_to = ColumnString::create();
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ColumnString::Chars & data_to = col_to->getChars();
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ColumnString::Offsets & offsets_to = col_to->getOffsets();
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offsets_to.resize(input_rows_count);
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const IColumn & length_column = *block.getByPosition(arguments[0]).column;
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IColumn::Offset offset = 0;
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for (size_t row_num = 0; row_num < input_rows_count; ++row_num)
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{
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size_t length = length_column.getUInt(row_num);
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if (length > (1 << 30))
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throw Exception("Too large string size in function " + getName(), ErrorCodes::TOO_LARGE_STRING_SIZE);
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IColumn::Offset next_offset = offset + length + 1;
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data_to.resize(next_offset);
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offsets_to[row_num] = next_offset;
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auto * data_to_ptr = data_to.data(); /// avoid assert on array indexing after end
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for (size_t pos = offset, end = offset + length; pos < end; pos += 4) /// We have padding in column buffers that we can overwrite.
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{
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UInt64 rand = thread_local_rng();
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UInt16 rand1 = rand;
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UInt16 rand2 = rand >> 16;
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UInt16 rand3 = rand >> 32;
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UInt16 rand4 = rand >> 48;
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/// Printable characters are from range [32; 126].
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/// https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
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data_to_ptr[pos + 0] = 32 + ((rand1 * 95) >> 16);
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data_to_ptr[pos + 1] = 32 + ((rand2 * 95) >> 16);
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data_to_ptr[pos + 2] = 32 + ((rand3 * 95) >> 16);
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data_to_ptr[pos + 3] = 32 + ((rand4 * 95) >> 16);
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/// NOTE gcc failed to vectorize this code (aliasing of char?)
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/// TODO Implement SIMD optimizations from Danila Kutenin.
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}
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data_to[offset + length] = 0;
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offset = next_offset;
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}
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block.getByPosition(result).column = std::move(col_to);
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}
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};
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void registerFunctionRandomPrintableASCII(FunctionFactory & factory)
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{
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factory.registerFunction<FunctionRandomPrintableASCII>();
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}
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}
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