doc/posix-headers/float.texi

@node float.h
@section @file{float.h}

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/float.h.html}

Gnulib module: float-h
@mindex float-h

Portability problems fixed by Gnulib:
@itemize
@item
The conversion from @code{int} to @code{long double} in incorrect on some
platforms:
glibc 2.7 on Linux/SPARC64.
@item
The values of @code{LDBL_*} macros are incorrect on some platforms:
On OpenBSD 4.0 and MirBSD 10, they are the same as the values of the
@code{DBL_*} macros, although @samp{long double} is a larger type than
@samp{double}.
On FreeBSD/x86 6.4, they represent the incorrect 53-bit precision assumptions
in the compiler, not the real 64-bit precision at runtime.
On PowerPC with gcc 8.3 and the default @option{-mabi=ibmlongdouble},
they don't reflect the ``double double'' representation of @code{long double}
correctly; the non-IEEE representation is tricky, as it is a pair of
IEEE @code{double} values such that adding the two elements and
rounding to even yields the high element of the pair, and arithmetic
overflow has undefined behavior instead of reliably yielding infinity.
@item
The macros
@code{FLT_HAS_SUBNORM}, @code{FLT_DECIMAL_DIG}, @code{FLT_TRUE_MIN},
@code{DBL_HAS_SUBNORM}, @code{DBL_DECIMAL_DIG}, @code{DBL_TRUE_MIN},
@code{LDBL_HAS_SUBNORM}, @code{LDBL_DECIMAL_DIG}, @code{LDBL_TRUE_MIN},
that were added in ISO C 11, are missing on some platforms:
gcc 4.5.4, clang 7, Solaris 11.3 with Sun C.
@item
The macro @code{LDBL_DECIMAL_DIG} is missing on some platforms:
MSVC 14.
@item
The value of macro @code{FLT_TRUE_MIN} is not a @code{float} on some platforms:
AIX 7.1 with xlc.
@item
The macros
@code{FLT_IS_IEC_60559}, @code{FLT_NORM_MAX}, @code{FLT_SNAN},
@code{DBL_IS_IEC_60559}, @code{DBL_NORM_MAX}, @code{DBL_SNAN},
@code{LDBL_IS_IEC_60559}, @code{LDBL_NORM_MAX}, @code{LDBL_SNAN},
that were added in ISO C 23, are missing on some platforms:
gcc 14 without @code{-std=c23} or @code{-std=gnu23}, clang 18, musl libc 1.2.5, AIX 7.3 with xlclang, Solaris 11.3 with Sun C, MSVC 14.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
The macro @code{FLT_ROUNDS} is a constant expression and does not represent
the current rounding mode on some platforms:
glibc 2.11, HP-UX 11, mingw.
@item
The value of @code{FLT_TRUE_MIN} is not a constant on some platforms:
FreeBSD/x86.
@item
The values of @code{FLT_SNAN}, @code{DBL_SNAN}, @code{LDBL_SNAN} are not
constants on some platforms:
AIX 7.3 with xlclang, and all platforms which use the gnulib replacements.
@end itemize