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Update isfinite declaration to be constexpr for c++23 only #3746

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Update isfinite declaration to be constexpr for c++23 only #3746

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2 changes: 1 addition & 1 deletion include/fmt/format.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2752,7 +2752,7 @@ template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&&
has_isfinite<T>::value)>
FMT_CONSTEXPR20 bool isfinite(T value) {
constexpr T inf = T(std::numeric_limits<double>::infinity());
if (is_constant_evaluated())
if (is_constant_evaluated(true))
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One drawback is that it switches to a slightly worse implementation on older systems: https://www.godbolt.org/z/WWzjEsrxj. But I guess we can optimize it later.

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I don't see an alternative other than testing FMT_CONSTEXPR20 in the body to replace is_constant_evaluated :(

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We can use __builtin_is_constant_evaluated instead of std::is_constant_evaluated.

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@phprus phprus Dec 13, 2023 •
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Or we can improve

fmt/include/fmt/core.h

Lines 108 to 110 in 89860eb

#if ((FMT_CPLUSPLUS >= 202002L) && \
(!defined(_GLIBCXX_RELEASE) || _GLIBCXX_RELEASE > 9)) || \
(FMT_CPLUSPLUS >= 201709L && FMT_GCC_VERSION >= 1002)

condition by adding a stdlib version check.

@hchataing, which version of libc++ (_LIBCPP_VERSION) or libstdc++ (_GLIBCXX_RELEASE) you are using?

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@hchataing check PR #3754 please

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Neither macro is defined by the compiler... but maybe I am checking wrong (clang++ -std=c++20 -E -dM foo.cc)

return !detail::isnan(value) && value < inf && value > -inf;
return std::isfinite(value);
}
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