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Floating Point Edge Case in ccmath::abs #871

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mborland opened this issue Nov 11, 2022 · 0 comments · Fixed by #872
Closed

Floating Point Edge Case in ccmath::abs #871

mborland opened this issue Nov 11, 2022 · 0 comments · Fixed by #872

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@mborland
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From the ML:

Hi Matt,
ccmath::abs() gives wrong result for FP-values std::numeric_limits<FP-Type>::min() in constexpr context.

test case:
using type = float;
constexpr type
	a = std::numeric_limits<type>::min(),
	b = boost::math::ccmath::abs(a);
std::cout << a << std::endl << b << std::endl;

1.17549e-38
nan


The Problem is:
template <typename T>
inline constexpr T abs_impl(T x) noexcept
{
    return boost::math::ccmath::isnan(x) ? std::numeric_limits<T>::quiet_NaN() :
           boost::math::ccmath::isinf(x) ? std::numeric_limits<T>::infinity() :
           x == -0 ? T(0) :
           x == (std::numeric_limits<T>::min)() ? std::numeric_limits<T>::quiet_NaN() :
           x > 0 ? x : -x;
}

In the case of FP-types, only the sign-bit has to be deleted, since one cannot assume that quiet_NaN() and/or signaling_NaN() are always unsigned.


thx
Gero
mborland added a commit to mborland/math that referenced this issue Nov 11, 2022
@mborland mborland linked a pull request Nov 11, 2022 that will close this issue
mborland added a commit that referenced this issue Nov 13, 2022
AZero13 pushed a commit to AZero13/math that referenced this issue Nov 26, 2022
mborland added a commit that referenced this issue Dec 7, 2022
mborland added a commit that referenced this issue Dec 8, 2022
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