ClickHouse/src/Functions/DivisionUtils.h

#pragma once

#include <cmath>
#include <type_traits>
#include <Common/Exception.h>
#include <DataTypes/NumberTraits.h>

#if !defined(ARCADIA_BUILD)
#    include <Common/config.h>
#endif

namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_DIVISION;
}

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsign-compare"

template <typename A, typename B>
inline void throwIfDivisionLeadsToFPE(A a, B b)
{
    /// Is it better to use siglongjmp instead of checks?

    if (unlikely(b == 0))
        throw Exception("Division by zero", ErrorCodes::ILLEGAL_DIVISION);

    /// http://avva.livejournal.com/2548306.html
    if (unlikely(is_signed_v<A> && is_signed_v<B> && a == std::numeric_limits<A>::min() && b == -1))
        throw Exception("Division of minimal signed number by minus one", ErrorCodes::ILLEGAL_DIVISION);
}

template <typename A, typename B>
inline bool divisionLeadsToFPE(A a, B b)
{
    if (unlikely(b == 0))
        return true;

    if (unlikely(is_signed_v<A> && is_signed_v<B> && a == std::numeric_limits<A>::min() && b == -1))
        return true;

    return false;
}

template <typename A, typename B>
inline auto checkedDivision(A a, B b)
{
    throwIfDivisionLeadsToFPE(a, b);

    if constexpr (is_big_int_v<A> && std::is_floating_point_v<B>)
        return bigint_cast<B>(a) / b;
    else if constexpr (is_big_int_v<B> && std::is_floating_point_v<A>)
        return a / bigint_cast<A>(b);
    else if constexpr (is_big_int_v<A> && is_big_int_v<B>)
        return static_cast<A>(a / b);
    else if constexpr (!is_big_int_v<A> && is_big_int_v<B>)
        return static_cast<A>(B(a) / b);
    else
        return a / b;
}


#pragma GCC diagnostic pop

template <typename A, typename B>
struct DivideIntegralImpl
{
    using ResultType = typename NumberTraits::ResultOfIntegerDivision<A, B>::Type;
    static const constexpr bool allow_fixed_string = false;

    template <typename Result = ResultType>
    static inline Result apply(A a, B b)
    {
        using CastA = std::conditional_t<is_big_int_v<B> && std::is_same_v<A, UInt8>, uint8_t, A>;
        using CastB = std::conditional_t<is_big_int_v<A> && std::is_same_v<B, UInt8>, uint8_t, B>;

        /// Otherwise overflow may occur due to integer promotion. Example: int8_t(-1) / uint64_t(2).
        /// NOTE: overflow is still possible when dividing large signed number to large unsigned number or vice-versa. But it's less harmful.
        if constexpr (is_integer_v<A> && is_integer_v<B> && (is_signed_v<A> || is_signed_v<B>))
        {
            using SignedCastA = make_signed_t<CastA>;
            using SignedCastB = std::conditional_t<sizeof(A) <= sizeof(B), make_signed_t<CastB>, SignedCastA>;

            return bigint_cast<Result>(checkedDivision(bigint_cast<SignedCastA>(a), bigint_cast<SignedCastB>(b)));
        }
        else
            return bigint_cast<Result>(checkedDivision(CastA(a), CastB(b)));
    }

#if USE_EMBEDDED_COMPILER
    static constexpr bool compilable = false; /// don't know how to throw from LLVM IR
#endif
};

template <typename A, typename B>
struct ModuloImpl
{
    using ResultType = typename NumberTraits::ResultOfModulo<A, B>::Type;
    using IntegerAType = typename NumberTraits::ToInteger<A>::Type;
    using IntegerBType = typename NumberTraits::ToInteger<B>::Type;

    static const constexpr bool allow_fixed_string = false;

    template <typename Result = ResultType>
    static inline Result apply(A a, B b)
    {
        if constexpr (std::is_floating_point_v<ResultType>)
        {
            /// This computation is similar to `fmod` but the latter is not inlined and has 40 times worse performance.
            return bigint_cast<ResultType>(a) - trunc(bigint_cast<ResultType>(a) / bigint_cast<ResultType>(b)) * bigint_cast<ResultType>(b);
        }
        else
        {
            throwIfDivisionLeadsToFPE(IntegerAType(a), IntegerBType(b));

            if constexpr (is_big_int_v<IntegerAType> || is_big_int_v<IntegerBType>)
            {
                using CastA = std::conditional_t<std::is_same_v<IntegerAType, UInt8>, uint8_t, IntegerAType>;
                using CastB = std::conditional_t<std::is_same_v<IntegerBType, UInt8>, uint8_t, IntegerBType>;

                CastA int_a(a);
                CastB int_b(b);

                if constexpr (is_big_int_v<IntegerBType> && sizeof(IntegerAType) <= sizeof(IntegerBType))
                    return bigint_cast<Result>(bigint_cast<CastB>(int_a) % int_b);
                else
                    return bigint_cast<Result>(int_a % bigint_cast<CastA>(int_b));
            }
            else
                return IntegerAType(a) % IntegerBType(b);
        }
    }

#if USE_EMBEDDED_COMPILER
    static constexpr bool compilable = false; /// don't know how to throw from LLVM IR
#endif
};

}