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Merge pull request #13510 from ClickHouse/fix-assert-lcm

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Fix assert in "lcm"
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alexey-milovidov 2020-08-08 17:02:56 +03:00 committed by GitHub
commit 3af1eba808
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3 changed files with 56 additions and 3 deletions
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41
src/Functions/lcm.cpp
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@ -1,6 +1,28 @@
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionBinaryArithmetic.h>
#include <numeric>
#include <limits>
#include <type_traits>
namespace
{
template <typename T>
constexpr T abs(T value) noexcept
{
if constexpr (std::is_signed_v<T>)
{
if (value >= 0 || value == std::numeric_limits<T>::min())
return value;
return -value;
}
else
return value;
}
}
namespace DB
@ -18,9 +40,22 @@ struct LCMImpl
{
throwIfDivisionLeadsToFPE(typename NumberTraits::ToInteger<A>::Type(a), typename NumberTraits::ToInteger<B>::Type(b));
throwIfDivisionLeadsToFPE(typename NumberTraits::ToInteger<B>::Type(b), typename NumberTraits::ToInteger<A>::Type(a));
return std::lcm(
typename NumberTraits::ToInteger<Result>::Type(a),
typename NumberTraits::ToInteger<Result>::Type(b));
/** It's tempting to use std::lcm function.
* But it has undefined behaviour on overflow.
* And assert in debug build.
* We need some well defined behaviour instead
* (example: throw an exception or overflow in implementation specific way).
*/
using Int = typename NumberTraits::ToInteger<Result>::Type;
using Unsigned = std::make_unsigned_t<Int>;
Unsigned val1 = abs<Int>(a) / std::gcd(Int(a), Int(b));
Unsigned val2 = abs<Int>(b);
/// Overflow in implementation specific way.
return Result(val1 * val2);
}
#if USE_EMBEDDED_COMPILER

8
tests/queries/0_stateless/01435_lcm_overflow.reference Normal file
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10
tests/queries/0_stateless/01435_lcm_overflow.sql Normal file
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@ -0,0 +1,10 @@
SELECT lcm(15, 10);
SELECT lcm(-15, 10);
SELECT lcm(15, -10);
SELECT lcm(-15, -10);
-- Implementation specific result on overflow:
SELECT ignore(lcm(256, 9223372036854775807));
SELECT ignore(lcm(256, -9223372036854775807));
SELECT ignore(lcm(-256, 9223372036854775807));
SELECT ignore(lcm(-256, -9223372036854775807));