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| author | Marius Hillenbrand <mhillen@linux.ibm.com> | 2020-11-30 15:53:59 +0100 |
|---|---|---|
| committer | Stefan Liebler <stli@linux.ibm.com> | 2020-12-09 16:26:46 +0100 |
| commit | f88242af19dc970949806790f70c6fd6336944a6 (patch) | |
| tree | 5dbc966ce8356ff8b3f5515f151f2c7de4e61f7e | |
| parent | b5eeca8cfd9d0fd92b5633a88901d9ff27f2b496 (diff) | |
| download | glibc-f88242af19dc970949806790f70c6fd6336944a6.zip glibc-f88242af19dc970949806790f70c6fd6336944a6.tar.gz glibc-f88242af19dc970949806790f70c6fd6336944a6.tar.bz2 | |
S390: Derive float_t from FLT_EVAL_METHOD
float_t supposedly represents the type that is used to evaluate float
expressions internally. While the isa supports single-precision float
operations, the port of glibc to s390 incorrectly deferred to the
generic definitions which, back then, tied float_t to double. gcc by
default evaluates float in single precision, so that scenario violates
the C standard (sections 5.2.4.2.2 and 7.12 in C11/C17). With
-fexcess-precision=standard, gcc evaluates float in double precision,
which aligns with the standard yet at the cost of added conversion
instructions.
With this patch, we drop the s390-specific definition of float_t and
defer to the default behavior, which aligns float_t with the
compiler-defined FLT_EVAL_METHOD in a standard-compliant way.
Checked on s390x-linux-gnu with 31-bit and 64-bit builds.
| -rw-r--r-- | NEWS | 7 | ||||
| -rw-r--r-- | sysdeps/s390/bits/flt-eval-method.h | 24 |
2 files changed, 7 insertions, 24 deletions
@@ -46,6 +46,13 @@ Deprecated and removed features, and other changes affecting compatibility: program is now installed in the /usr/bin subdirectory. Previously, the /usr/sbin subdirectory was used. +* On s390(x), the type float_t is now derived from the macro + __FLT_EVAL_METHOD__ that is defined by the compiler, instead of being + hardcoded to double. This does not affect the ABI of any libraries + that are part of the GNU C Library, but may affect the ABI of other + libraries that use this type in their interfaces. The new definition + improves consistency with compiler behavior in many scenarios. + Changes to build and runtime requirements: * On Linux, the system administrator needs to configure /dev/pts with diff --git a/sysdeps/s390/bits/flt-eval-method.h b/sysdeps/s390/bits/flt-eval-method.h deleted file mode 100644 index 826bbfe..0000000 --- a/sysdeps/s390/bits/flt-eval-method.h +++ /dev/null @@ -1,24 +0,0 @@ -/* Define __GLIBC_FLT_EVAL_METHOD. S/390 version. - Copyright (C) 2016-2020 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - <https://www.gnu.org/licenses/>. */ - -#ifndef _MATH_H -# error "Never use <bits/flt-eval-method.h> directly; include <math.h> instead." -#endif - -/* This value is used because of a historical mistake. */ -#define __GLIBC_FLT_EVAL_METHOD 1 |