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91 lines
2.4 KiB
C++
91 lines
2.4 KiB
C++
#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionBinaryArithmetic.h>
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#include <numeric>
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#include <limits>
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#include <type_traits>
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namespace
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{
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template <typename T>
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constexpr T abs(T value) noexcept
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{
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if constexpr (std::is_signed_v<T>)
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{
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if (value >= 0 || value == std::numeric_limits<T>::min())
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return value;
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return -value;
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}
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else
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return value;
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}
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}
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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 NOT_IMPLEMENTED;
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}
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namespace
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{
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template <typename A, typename B>
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struct LCMImpl
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{
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using ResultType = typename NumberTraits::ResultOfAdditionMultiplication<A, B>::Type;
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static const constexpr bool allow_fixed_string = false;
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template <typename Result = ResultType>
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static inline std::enable_if_t<is_big_int_v<A> || is_big_int_v<B> || is_big_int_v<Result>, Result>
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apply([[maybe_unused]] A a, [[maybe_unused]] B b)
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{
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throw Exception("LCM is not implemented for big integers", ErrorCodes::NOT_IMPLEMENTED);
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}
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template <typename Result = ResultType>
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static inline std::enable_if_t<!is_big_int_v<A> && !is_big_int_v<B> && !is_big_int_v<Result>, Result>
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apply([[maybe_unused]] A a, [[maybe_unused]] B b)
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{
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throwIfDivisionLeadsToFPE(typename NumberTraits::ToInteger<A>::Type(a), typename NumberTraits::ToInteger<B>::Type(b));
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throwIfDivisionLeadsToFPE(typename NumberTraits::ToInteger<B>::Type(b), typename NumberTraits::ToInteger<A>::Type(a));
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/** It's tempting to use std::lcm function.
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* But it has undefined behaviour on overflow.
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* And assert in debug build.
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* We need some well defined behaviour instead
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* (example: throw an exception or overflow in implementation specific way).
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*/
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using Int = typename NumberTraits::ToInteger<Result>::Type;
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using Unsigned = make_unsigned_t<Int>;
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Unsigned val1 = abs<Int>(a) / std::gcd(Int(a), Int(b));
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Unsigned val2 = abs<Int>(b);
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/// Overflow in implementation specific way.
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return Result(val1 * val2);
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}
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#if USE_EMBEDDED_COMPILER
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static constexpr bool compilable = false; /// exceptions (and a non-trivial algorithm)
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#endif
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};
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struct NameLCM { static constexpr auto name = "lcm"; };
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using FunctionLCM = BinaryArithmeticOverloadResolver<LCMImpl, NameLCM, false>;
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}
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void registerFunctionLCM(FunctionFactory & factory)
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{
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factory.registerFunction<FunctionLCM>();
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}
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}
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