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Implement constexpr isfinite to avoid producing NaN

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This commit is contained in:
Victor Zverovich
2022-05-11 07:21:09 -07:00
parent 358f5a7e50
commit ae963e444f
2 changed files with 9 additions and 3 deletions
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10
include/fmt/format.h
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@ -2343,12 +2343,16 @@ struct has_isfinite<T, enable_if_t<sizeof(std::isfinite(T())) != 0>>
template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&& template <typename T, FMT_ENABLE_IF(std::is_floating_point<T>::value&&
has_isfinite<T>::value)> has_isfinite<T>::value)>
FMT_CONSTEXPR20 bool isfinite(T value) { FMT_CONSTEXPR20 bool isfinite(T value) {
if (is_constant_evaluated()) return !isnan(value - value); constexpr T inf = T(std::numeric_limits<double>::infinity());
if (is_constant_evaluated())
return !isnan(value) && value != inf && value != -inf;
return std::isfinite(value); return std::isfinite(value);
} }
template <typename T, FMT_ENABLE_IF(!has_isfinite<T>::value)> template <typename T, FMT_ENABLE_IF(!has_isfinite<T>::value)>
constexpr bool isfinite(T value) { FMT_CONSTEXPR bool isfinite(T value) {
return value - value == 0; // std::isfinite doesn't support __float128. T inf = T(std::numeric_limits<double>::infinity());
// std::isfinite doesn't support __float128.
return !isnan(value) && value != inf && value != -inf;
} }
template <typename T, FMT_ENABLE_IF(is_floating_point<T>::value)> template <typename T, FMT_ENABLE_IF(is_floating_point<T>::value)>

2
test/format-test.cc
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@ -89,6 +89,8 @@ template <typename Float> void check_isfinite() {
EXPECT_TRUE(isfinite(Float(fmt::detail::max_value<double>()))); EXPECT_TRUE(isfinite(Float(fmt::detail::max_value<double>())));
// Use double because std::numeric_limits is broken for __float128. // Use double because std::numeric_limits is broken for __float128.
using limits = std::numeric_limits<double>; using limits = std::numeric_limits<double>;
FMT_CONSTEXPR20 auto result = isfinite(Float(limits::infinity()));
EXPECT_FALSE(result);
EXPECT_FALSE(isfinite(Float(limits::infinity()))); EXPECT_FALSE(isfinite(Float(limits::infinity())));
EXPECT_FALSE(isfinite(Float(-limits::infinity()))); EXPECT_FALSE(isfinite(Float(-limits::infinity())));
EXPECT_FALSE(isfinite(Float(limits::quiet_NaN()))); EXPECT_FALSE(isfinite(Float(limits::quiet_NaN())));