mirror of git://sourceware.org/git/glibc.git
f280fa6d17
sysdeps/ieee754/dbl-64/dla.h can use a macro DLA_FMS for more efficient double-width operations when fused multiply-subtract is supported. However, this macro is only defined for x86_64, conditional on architecture-specific __FMA4__. This patch makes the code use __builtin_fma conditional on __FP_FAST_FMA, as used elsewhere in glibc. Tested for x86_64, x86 and powerpc. On powerpc (where this is causing fused operations to be used where they weren't previously) I see an increase from 1ulp to 2ulp in the imaginary part of clog10: testing double (without inline functions) Failure: Test: Imaginary part of: clog10 (0x1.7a858p+0 - 0x6.d940dp-4 i) Result: is: -1.2237865208199886e-01 -0x1.f5435146bb61ap-4 should be: -1.2237865208199888e-01 -0x1.f5435146bb61cp-4 difference: 2.7755575615628914e-17 0x1.0000000000000p-55 ulp : 2.0000 max.ulp : 1.0000 Maximal error of real part of: clog10 is : 3 ulp accepted: 3 ulp Maximal error of imaginary part of: clog10 is : 2 ulp accepted: 1 ulp This is actually resulting from atan2 becoming *more* accurate (atan2 (-0x6.d940dp-4, 0x1.7a858p+0) should ideally be -0x1.208cd6e841554p-2 but was -0x1.208cd6e841555p-2 from a powerpc libm built before this change, and is -0x1.208cd6e841554p-2 from a powerpc libm built after this change). Since these functions are not expected to be correctly rounding by glibc's accuracy goals, neither result is a problem, but this does imply that some of this code, although designed to be correctly rounding, is not in fact correctly rounding (possibly because of GCC creating fused operations where the code does not expect it, something we've only disabled for specific functions where it was found to cause large errors). (Of course as previously discussed I think we should remove the slow cases where an error analysis shows this wouldn't increase the errors much above 0.5ulp; it's only functions such as cratan2 that are expected to be correctly rounding, not atan2.) * sysdeps/ieee754/dbl-64/dla.h [__FP_FAST_FMA] (DLA_FMS): Define macro to use __builtin_fma. * sysdeps/x86_64/fpu/dla.h: Remove file. |
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README
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. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 3.2 or later on all architectures except i[4567]86 and x86_64, where Linux kernel version 2.6.32 or later suffices. 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 arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. 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 sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu If you are interested in doing a port, please contact the glibc maintainers; see http://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 http://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 http://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.