ClickHouse

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#include <Functions/FunctionFactory.h>
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#include <Functions/FunctionBinaryArithmetic.h>
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#include <Core/AccurateComparison.h>
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#include <Functions/LeastGreatestGeneric.h>
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namespace DB
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{
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template <typename A, typename B>
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struct GreatestBaseImpl
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{
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    using ResultType = NumberTraits::ResultOfGreatest<A, B>;
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    static const constexpr bool allow_fixed_string = false;
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    static const constexpr bool allow_string_integer = false;
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    template <typename Result = ResultType>
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    static inline Result apply(A a, B b)
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    {
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        return static_cast<Result>(a) > static_cast<Result>(b) ?
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               static_cast<Result>(a) : static_cast<Result>(b);
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    }
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#if USE_EMBEDDED_COMPILER
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    static constexpr bool compilable = true;
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    static inline llvm::Value * compile(llvm::IRBuilder<> & b, llvm::Value * left, llvm::Value * right, bool is_signed)
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    {
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        if (!left->getType()->isIntegerTy())
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        {
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            /// Follows the IEEE-754 semantics for maxNum except for the handling of signaling NaNs. This matches the behavior of libc fmax.
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            return b.CreateMaxNum(left, right);
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        }
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        auto * compare_value = is_signed ? b.CreateICmpSGT(left, right) : b.CreateICmpUGT(left, right);
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        return b.CreateSelect(compare_value, left, right);
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    }
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#endif
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};
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template <typename A, typename B>
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struct GreatestSpecialImpl
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{
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    using ResultType = make_unsigned_t<A>;
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    static const constexpr bool allow_fixed_string = false;
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    static const constexpr bool allow_string_integer = false;
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    template <typename Result = ResultType>
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    static inline Result apply(A a, B b)
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    {
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        static_assert(std::is_same_v<Result, ResultType>, "ResultType != Result");
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        return accurate::greaterOp(a, b) ? static_cast<Result>(a) : static_cast<Result>(b);
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    }
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#if USE_EMBEDDED_COMPILER
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    static constexpr bool compilable = false; /// ???
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#endif
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};
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template <typename A, typename B>
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using GreatestImpl = std::conditional_t<!NumberTraits::LeastGreatestSpecialCase<A, B>, GreatestBaseImpl<A, B>, GreatestSpecialImpl<A, B>>;
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struct NameGreatest { static constexpr auto name = "greatest"; };
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using FunctionGreatest = FunctionBinaryArithmetic<GreatestImpl, NameGreatest>;
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REGISTER_FUNCTION(Greatest)
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{
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    factory.registerFunction<LeastGreatestOverloadResolver<LeastGreatest::Greatest, FunctionGreatest>>({}, FunctionFactory::CaseInsensitive);
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}
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}
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