* type promotion for fixed point types
@ 2009-02-27 20:58 Sean D'Epagnier
2009-02-27 21:07 ` Joseph S. Myers
0 siblings, 1 reply; 2+ messages in thread
From: Sean D'Epagnier @ 2009-02-27 20:58 UTC (permalink / raw)
To: gcc, fu
Hi,
I just added support for printf and scanf of fixed point types to avr
libc. I wanted to handle:
Currently "accum" and "fract" work, but not "short accum" or "short fract"
This is not a problem for integers currently since they get type
promoted when passed with stdarg.
There is nothing in the fixed-point standard that is for or against
this.. it seems logical that "short accum" be promoted to "accum" and
"short fract" be promoted to "fract" in this case.
Does anyone have any opinions on this?
Thanks,
Sean
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: type promotion for fixed point types
2009-02-27 20:58 type promotion for fixed point types Sean D'Epagnier
@ 2009-02-27 21:07 ` Joseph S. Myers
0 siblings, 0 replies; 2+ messages in thread
From: Joseph S. Myers @ 2009-02-27 21:07 UTC (permalink / raw)
To: Sean D'Epagnier; +Cc: gcc, fu
On Fri, 27 Feb 2009, Sean D'Epagnier wrote:
> Hi,
>
> I just added support for printf and scanf of fixed point types to avr
> libc. I wanted to handle:
>
> Currently "accum" and "fract" work, but not "short accum" or "short fract"
>
> This is not a problem for integers currently since they get type
> promoted when passed with stdarg.
>
> There is nothing in the fixed-point standard that is for or against
> this.. it seems logical that "short accum" be promoted to "accum" and
> "short fract" be promoted to "fract" in this case.
>
> Does anyone have any opinions on this?
The promotion of "float" to "double" when passed to a variadic function is
considered a legacy anomaly. Thus, the default argument promotions
(applied to variable arguments) should be considered to be the "integer
promotions", float to double, and nothing else. (In particular, it is
deliberate that float _Complex does not promote to double _Complex - see
DR#206 - and likewise float _Imaginary (not supported by GCC) does not
promote to double _Imaginary.)
Unless your promotion is defined as being one of the "integer promotions",
it should thus not occur. Your printf implementation should call va_arg
with the correct unpromoted type when it is passed an appropriate one of
the fixed-point printf formats defined in the fixed-point TR.
--
Joseph S. Myers
joseph@codesourcery.com
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2009-02-27 21:07 ` Joseph S. Myers
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