Re: [RFC][PATCH] MIPS: IEEE 754-2008 NaN encoding support

[Rich Felker <dalias@aerifal.cx>]

On Fri, Aug 23, 2013 at 12:52:43AM +0100, Maciej W. Rozycki wrote:
>  As many of you have been aware it has been a long practice for software 
> using IEEE 754 floating-point arithmetic run on MIPS processors to use an 
> encoding of Not-a-Number (NaN) data different to one used by software run 
> on other processors.  And as of IEEE 754-2008 revision [1] this encoding 
> does not follow one recommended in the standard, as specified in section 
> 6.2.1, where it is stated that quiet NaNs should have the first bit (d1) 
> of their significand set to 1 while signalling NaNs should have that bit 
> set to 0, but MIPS software interprets the two bits in the opposite 
> manner.
> 
>  As from revision 3.50 [2][3] the MIPS Architecture provides for 
> processors that support the IEEE 754-2008 preferred NaN encoding format.  
> As the two formats (further referred to as "legacy NaN" and "2008 NaN") 
> are incompatible to each other, tools will have to provide support for the 
> two formats to help people avoid using incompatible binary modules.  Here 
> is the glibc part.

Can you elaborate on why you think this is an ABI issue? IMO it's just
s runtime issue unless you're considering raw floating point data
written to disk. In any case this seems like such a small issue that
it should just be silently fixed, rather than adding huge amounts of
ABI ugliness.

Rich