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s390x: derive float_t from compiler or default to float

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float_t should represent the type that is used to evaluate float
expressions internally. On s390x, float_t is currently set to double.
In contrast, the isa supports single-precision float operations and
compilers by default evaluate float in single precision, which
violates the C standard (sections 5.2.4.2.2 and 7.12 in C11/C17, to be
precise). With -fexcess-precision=standard, gcc evaluates float in
double precision, which aligns with the standard yet at the cost of
added conversion instructions.

gcc-11 will drop the special case to retrofit double precision
behavior for -fexcess-precision=standard so that __FLT_EVAL_METHOD__
will be 0 on s390x in any scenario.

To improve standards compliance and compatibility with future compiler
direction, this patch changes the definition of float_t to be derived
from the compiler's __FLT_EVAL_METHOD__.
This commit is contained in:
Marius Hillenbrand 2020-12-01 15:36:34 +01:00 committed by Rich Felker
parent 821083ac7b
commit 738c4e945c
2 changed files with 9 additions and 1 deletions
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4
arch/s390x/bits/alltypes.h.in
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@ -9,7 +9,11 @@
TYPEDEF int wchar_t;
#endif
#if defined(__FLT_EVAL_METHOD__) && __FLT_EVAL_METHOD__ == 1
TYPEDEF double float_t;
#else
TYPEDEF float float_t;
#endif
TYPEDEF double double_t;
TYPEDEF struct { long long __ll; long double __ld; } max_align_t;

6
arch/s390x/bits/float.h
View File

@ -1,4 +1,8 @@
#define FLT_EVAL_METHOD 1
#ifdef __FLT_EVAL_METHOD__
#define FLT_EVAL_METHOD __FLT_EVAL_METHOD__
#else
#define FLT_EVAL_METHOD 0
#endif
#define LDBL_TRUE_MIN 6.47517511943802511092443895822764655e-4966L
#define LDBL_MIN 3.36210314311209350626267781732175260e-4932L