Re: [PATCH, Fortran] Revert to non-multilib-specific ISO_Fortran_binding.h

[Tobias Burnus <tobias@codesourcery.com>]

Hi Gerald,

I note:

On 13.09.21 17:56, Gerald Pfeifer wrote:
> % egrep -r '#define.*LDBL_(MANT_DIG|MIN_EXP|MAX_EXP)'/usr/include/
> /usr/include/x86/float.h:#define LDBL_MANT_DIG  64
> /usr/include/x86/float.h:#define LDBL_MIN_EXP   (-16381)
> /usr/include/x86/float.h:#define LDBL_MAX_EXP   16384
>
> This looks like it matches existing Linux case already in place?
On 14.09.21 16:50, Gerald Pfeifer wrote:
> On Mon, 13 Sep 2021, Tobias Burnus wrote:
>> Can you run 'echo | cpp -E -g3|grep DBL' to (or in the build dir: echo |
>> ./gcc/cc1 -E -g3 -dD|grep DBL) to check what's the output?
> Thank you, Tobias, and I'm just testing the proposed patch, but still
> wanted to follow up on your question:
>
>    % echo | ./gcc/cc1 -E -g3 -dD | grep DBL
>    #define __DBL_MANT_DIG__ 53
>    #define __DBL_MIN_EXP__ (-1021)
>    #define __DBL_MAX_EXP__ 1024
>
>    #define __LDBL_MANT_DIG__ 53
>    #define __LDBL_MIN_EXP__ (-16381)
>    #define __LDBL_MAX_EXP__ 16384

I note that LDBL_MANT_DIG is 53 as for "double" – while Linux
and your header file has 64. On the other hand, MIN/MAX_EXP for
"long double" are larger than "double" – and match the values
from Linux and the size in your header file.

Thus, the first question is: why does DBL_MANT_DIG differ (64 vs. 53)?

And, related, does the following make sense and fixes the issue?

--- a/libgfortran/ISO_Fortran_binding.h
+++ b/libgfortran/ISO_Fortran_binding.h
@@ -228,5 +228,5 @@ extern int CFI_setpointer (CFI_cdesc_t *, CFI_cdesc_t *, const CFI_index_t []);

  /* This is the 80-bit encoding on x86; Fortran assigns it kind 10.  */
-#elif (LDBL_MANT_DIG == 64 \
+#elif ((LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 53) \
         && LDBL_MIN_EXP == -16381 \
         && LDBL_MAX_EXP == 16384)

Tobias

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