Home Original page

[PATCH] MIPS: IEEE 754-2008 NaN encoding features

Richard Sandiford rdsandiford@googlemail.com
Sat Dec 8 10:00:00 GMT 2012 
"Maciej W. Rozycki" <macro@codesourcery.com> writes:
> Hi,
>
>  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 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.
>
>  An upcoming MIPS Architecture revision will provide 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 binutils part.
>
>  Two new entities have been added to support static and dynamic linking.  
> For the former a set of new ELF file attribute values have been defined.  
> For the latter a new ELF file header flag has been defined.  These changes 
> are described in detail below.

But an ELF flag supports static and dynamic linking on its own.
Encoding the same information in the attribute seems redundant,
and makes the implementation a fair bit more complicated.

Richard
More information about the Binutils mailing list