ClickHouse/src/Functions/DivisionUtils.h
Alexey Milovidov e93e0afd52 Added a comment
2020-07-21 13:20:09 +03:00

108 lines
3.2 KiB
C++

#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);
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)
{
/// 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_integral_v<A> && is_integral_v<B> && (is_signed_v<A> || is_signed_v<B>))
return checkedDivision(std::make_signed_t<A>(a),
sizeof(A) > sizeof(B) ? std::make_signed_t<A>(b) : std::make_signed_t<B>(b));
else
return checkedDivision(a, 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;
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 ResultType(a) - trunc(ResultType(a) / ResultType(b)) * ResultType(b);
}
else
{
throwIfDivisionLeadsToFPE(typename NumberTraits::ToInteger<A>::Type(a), typename NumberTraits::ToInteger<B>::Type(b));
return typename NumberTraits::ToInteger<A>::Type(a) % typename NumberTraits::ToInteger<B>::Type(b);
}
}
#if USE_EMBEDDED_COMPILER
static constexpr bool compilable = false; /// don't know how to throw from LLVM IR
#endif
};
}