[PATCH] Aarch32/64: Support __FLT_EVAL_METHOD__ values other than 0, 1, 2
Torbjorn SVENSSON
torbjorn.svensson@st.com
Mon Apr 4 09:32:41 GMT 2022
Hello,
It would have been easier to review the patch if it was inline, but this will have to do anyway.
I think there is a typo in math.h. Aren't you supposed to do "#ifndef" and not "#ifdef"?
Kind regards,
Torbjörn
ST Restricted
-----Original Message-----
From: Newlib <newlib-bounces+torbjorn.svensson=st.com@sourceware.org> On Behalf Of Andrea Corallo
Sent: den 4 april 2022 10:39
To: newlib@sourceware.org
Cc: nd@arm.com
Subject: [PATCH] Aarch32/64: Support __FLT_EVAL_METHOD__ values other than 0, 1, 2
Hi all,
when _Float16 in native precision is supported GCC defines
__FLT_EVAL_METHOD__ to 16 as per ISO/IEC TS 18661-3.
Ex:
$ ./arm-none-eabi-gcc -mthumb -march=armv8.1-m.main+fp -mfloat-abi=softfp -xc /dev/null -E -dM | grep FLT_EVAL
#define __FLT_EVAL_METHOD__ 16
#define __FLT_EVAL_METHOD_TS_18661_3__ 16
Unfortunately libc/include/math.h understands only values 0, 1 and 2
leading to have newlib non compilable for those configurations.
I think in newlib we should either:
1- Handle __FLT_EVAL_METHOD__ == 16
2- Build in a C mode which does not enable _Float16 (ex -std=c11)
3- Build without the _FloatN extensions -fpermitted-flt-eval-methods=c11
I think 1 should be the favorite approach.
ISO/IEC 9899:201x [1] suggests that for other values of FLT_EVAL_METHOD
other than 0, 1, 2 the definition of float_t and double_t is
implementation-defined.
The suggested patch implements that for arm and Aarch64.
Note, some previous discussion on this topic can be found here [2] as
follow-up to a patch addressing the same issue (only for the
case__FLT_EVAL_METHOD__ == 16 case).
Best Regards
Andrea
[1] <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf>
[2] <https://sourceware.org/legacy-ml/newlib/2019/msg00597.html>
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