Re: CT-NG: floating point support in Newlibs printf?

["Yann E. MORIN" <yann dot morin dot 1998 at anciens dot enib dot fr>]

Jeppe, All,

On Monday 25 October 2010 16:56:51 Jeppe Ledet-Pedersen wrote:
> On 2010-10-25 08:54, Jeppe Ledet-Pedersen wrote:
> [--SNIP--]
> > If I i run "arm-unknown-eabi-cpp -dD" my toolchain defines both
> > __ARMEL__, __SOFTFP__ and __VFP_FP__ which should be taken into account
> > by Newlib in include/machine/ieeefp.h to use the correct floating point
> > format.
> [--SNIP--]
> 
> I have performed some further debugging of my floating point problems, 
> but I still don't have a solution.
> 
> __IEEE_LITTLE_ENDIAN is correctly set by include/machine/ieeefp.h and 
> consequently IEEE_8087 is defined in both stdlib/mprec.h and 
> stdio/vfieeefp.h. The macros word0()/word1() also appears to be set 
> correctly. _DOUBLE_IS_32BITS is not defined.
> 
> With my test code (http://pastebin.com/3Dsb9siL), I get the following 
> output:
> 
> 00 00 00 00 00 00 55 c0
> a is 0.000000
> 00 00 55 c0 00 00 00 00
> a (flipped) is -84.000000
> 
> According to "Format of VFP values" from the ARM Developer Suite 
> Developer Guide 
> (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0056d/Bcfibfha.html):
> 
> "in little-endian mode, the more significant word of a two-word 
> double-precision value, containing the exponent, has the higher address"
> 
> So it appears that GCC stores the double value in correct little-endian, 
> VFP format

Yes, it is good. I decoded by hand, and it is correct, AFAICS.

> but Newlib will only print it if converted to FPA format. I  
> have looked through the code for _vfprint_r and _dtoa_r but haven't 
> noticed anything suspicious.
> 
> Can any of you reproduce this behavior on your platforms?

Sorry, I don't have bare-metal + newlib.

> Suggestions to  
> what could be the culprit are very welcome. Maybe I should post my 
> question on the Newlib mailing list as well.

Yes, please send the issue there, and keep the list CCed.


Note that I'm leaving for ELC-E in Cambridge in ~8h (and I need to sleep
before that), and that I'll be back only by satruday late at night, so
don't expect any reaction before Sunday...

Regards,
Yann E. MORIN.

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