As described in bug 28358, the round-to-odd computations used in the
libm functions that round their results to a narrower format can yield
spurious underflow exceptions in the following circumstances: the
narrowing only narrows the precision of the type and not the exponent
range (i.e., it's narrowing _Float128 to _Float64x on x86_64, x86 or
ia64), the architecture does after-rounding tininess detection (which
applies to all those architectures), the result is inexact, tiny
before rounding but not tiny after rounding (with the chosen rounding
mode) for _Float64x (which is possible for narrowing mul, div and fma,
not for narrowing add, sub or sqrt), so the underflow exception
resulting from the toward-zero computation in _Float128 is spurious
for _Float64x.
Fixed by making ROUND_TO_ODD call feclearexcept (FE_UNDERFLOW) in the
problem cases (as indicated by an extra argument to the macro); there
is never any need to preserve underflow exceptions from this part of
the computation, because the conversion of the round-to-odd value to
the narrower type will underflow in exactly the cases in which the
function should raise that exception, but it may be more efficient to
avoid the extra manipulation of the floating-point environment when
not needed.
Tested for x86_64 and x86, and with build-many-glibcs.py.
This directory contains the sources of the GNU C Library.
See the file "version.h" for what release version you have.
The GNU C Library is the standard system C library for all GNU systems,
and is an important part of what makes up a GNU system. It provides the
system API for all programs written in C and C-compatible languages such
as C++ and Objective C; the runtime facilities of other programming
languages use the C library to access the underlying operating system.
In GNU/Linux systems, the C library works with the Linux kernel to
implement the operating system behavior seen by user applications.
In GNU/Hurd systems, it works with a microkernel and Hurd servers.
The GNU C Library implements much of the POSIX.1 functionality in the
GNU/Hurd system, using configurations i[4567]86-*-gnu.
When working with Linux kernels, this version of the GNU C Library
requires Linux kernel version 3.2 or later.
Also note that the shared version of the libgcc_s library must be
installed for the pthread library to work correctly.
The GNU C Library supports these configurations for using Linux kernels:
aarch64*-*-linux-gnu
alpha*-*-linux-gnu
arc*-*-linux-gnu
arm-*-linux-gnueabi
csky-*-linux-gnuabiv2
hppa-*-linux-gnu
i[4567]86-*-linux-gnu
x86_64-*-linux-gnu Can build either x86_64 or x32
ia64-*-linux-gnu
m68k-*-linux-gnu
microblaze*-*-linux-gnu
mips-*-linux-gnu
mips64-*-linux-gnu
powerpc-*-linux-gnu Hardware or software floating point, BE only.
powerpc64*-*-linux-gnu Big-endian and little-endian.
s390-*-linux-gnu
s390x-*-linux-gnu
riscv32-*-linux-gnu
riscv64-*-linux-gnu
sh[34]-*-linux-gnu
sparc*-*-linux-gnu
sparc64*-*-linux-gnu
If you are interested in doing a port, please contact the glibc
maintainers; see https://www.gnu.org/software/libc/ for more
information.
See the file INSTALL to find out how to configure, build, and install
the GNU C Library. You might also consider reading the WWW pages for
the C library at https://www.gnu.org/software/libc/.
The GNU C Library is (almost) completely documented by the Texinfo manual
found in the `manual/' subdirectory. The manual is still being updated
and contains some known errors and omissions; we regret that we do not
have the resources to work on the manual as much as we would like. For
corrections to the manual, please file a bug in the `manual' component,
following the bug-reporting instructions below. Please be sure to check
the manual in the current development sources to see if your problem has
already been corrected.
Please see https://www.gnu.org/software/libc/bugs.html for bug reporting
information. We are now using the Bugzilla system to track all bug reports.
This web page gives detailed information on how to report bugs properly.
The GNU C Library is free software. See the file COPYING.LIB for copying
conditions, and LICENSES for notices about a few contributions that require
these additional notices to be distributed. License copyright years may be
listed using range notation, e.g., 1996-2015, indicating that every year in
the range, inclusive, is a copyrightable year that would otherwise be listed
individually.