https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109758
Bug ID: 109758 Summary: quadmath abs Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: libquadmath Assignee: unassigned at gcc dot gnu.org Reporter: g.peterh...@t-online.de Target Milestone: --- Hello gcc-team, Problem: #include <boost/cstdfloat.hpp> #include <iostream> #include <limits> #include <cmath> using T = __float128; int main() { const T neg_nan_v = -std::numeric_limits<T>::quiet_NaN(); std::cout << neg_nan_v << std::endl; std::cout << "std::abs " << std::abs(neg_nan_v) << std::endl; std::cout << "fabsq " << fabsq(neg_nan_v) << std::endl; std::cout << "builtin " << __builtin_fabsf128(neg_nan_v) << std::endl; } -nan std::abs -nan fabsq nan builtin nan The problem can be found in bits/std_abs.h: #if !defined(__STRICT_ANSI__) && defined(_GLIBCXX_USE_FLOAT128) __extension__ inline _GLIBCXX_CONSTEXPR __float128 abs(__float128 __x) { return __x < 0 ? -__x : __x; } #endif Is this actually correct? If I compile with -U__STRICT_ANSI__ or remove/comment abs from bits/std_abs.h abs falls back to fabsq, which then also works. With std::abs(float/double/...) this problem does not occur. Wouldn't it make sense in principle to also provide a C++ header (quadmath.hpp)? #include <quadmath.h> namespace std { math-functions to_string/to_wstring to_chars/from_chars operator<< operator>> ... } thx Gero