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Re: [PATCH 4/4] powerpc64le: Enable float128
On Wed, 14 Jun 2017, Gabriel F. T. Gomes wrote:
> From: "Paul E. Murphy" <firstname.lastname@example.org>
> This patch adds ULPs for the float128 type, updates the abilist for libc
> and libm, and adds the files bits/floatn.h and float128-abi.h, in order to
> enable the new type for powerpc64le.
> This patch also adds the implementation of sqrtf128 for powerpc64le, since
> it is not implemented in libgcc. The sfp-machine.h header is taken from
> Tested for powerpc64, powerpc64le and s390x.
Have you tested with both GCC 6 and GCC 7?
> +* Support for ISO/IEC TS 18661-3:2015 is added. It is currently only
> + enabled for powerpc64le.
Well, no, support is added *for the float128 interfaces corresponding to
interfaces already implemented in glibc for other types*. That's a subset
of TS 18661-3 support and the summary needs to reflect that it is such a
subset. I'd say something like "Support is added, on powerpc64le, for
interfaces supporting the _Float128 type from ISO/IEC TS 18661-3:2015.
Most of the interfaces are taken from TS 18661-3. The type-generic macros
in <math.h> support this type, but those in <tgmath.h> do not. The GNU C
Library now requires GCC 6.2 or later to build for powerpc64le. When used
with GCC versions before GCC 7, these interfaces may be used with the type
under the non-standard name __float128.". Then list the interfaces, as
you do, but remembering the HUGE_VAL interfaces (standard) and M_*
> diff --git a/math/test-float128.h b/math/test-float128.h
> index 17c5928..f9a7e16 100644
> --- a/math/test-float128.h
> +++ b/math/test-float128.h
> @@ -20,6 +20,8 @@
> #include "test-math-floatn.h"
> /* Fixup builtins and constants for older compilers. */
> +#define __GLIBC_INTERNAL_STARTING_HEADER_IMPLEMENTATION
> +#include <bits/libc-header-start.h>
This should never be needed outside of installed headers. If you find you
need it, that indicates something is wrong elsewhere. <bits/floatn.h>
should not depend on anything from <bits/libc-header-start.h>.
__GLIBC_USE conditionals affected by <bits/libc-header-start.h> should
only appear in installed headers that themselves include it.
> +/* Defined to 1 if the current compiler invocation provides a
> + floating-point type with the IEEE 754 binary128 format, and this glibc
> + includes corresponding *f128 interfaces for it. */
> +#if defined _ARCH_PWR8 && defined __LITTLE_ENDIAN__ && (_CALL_ELF == 2) \
> + && defined __FLOAT128__ && !defined __cplusplus
> +# define __HAVE_FLOAT128 1
> +# define __HAVE_FLOAT128 0
Actually, I'd think it's desirable to be able to use the functions with
C++ (albeit that libstdc++ support would be its own project, but one that
depends on the functions being visible for C++). Which means not having
the __cplusplus conditional here, but instead using __float128 type name,
q suffix and __attribute__ ((__mode__ (__KC__))) for C++ even with GCC 7
and later. (The new built-in functions should work with GCC 7 for both C
> +# float128 requires adding a handful of extra flags.
> +%f128.o %f128.os %f128_r.o %f128_r.os: CFLAGS += -mfloat128
I think you need to use $(all-object-suffixes) or similar. This looks
like it would fail to add the option for .op objects (--enable-profile).
Or, more simply, you could just use -mfloat128 globally for building all
of glibc for powerpc64le, just as sysdeps/ieee754/ldbl-128ibm/Makefile
uses -mlong-double-128 unconditionally in sysdep-CFLAGS.
Joseph S. Myers