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Re: Minimum floating-point requirements


On Sat, 15 Feb 2014, Joseph S. Myers wrote:

> don't have a use for this breadth doesn't mean it's bad for GCC.  I would 
> welcome breadth in glibc in terms of additional non-default libm function 
> variants, such as __*_fast functions used with -ffast-math (which would be 
> built in the existing default mode, not the new non-default mode), if 
> people interested in those wish to contribute them.

To add: I don't know what other glibc developers would think of this, but 
I would consider the following acceptable:

* New __cbrtl_nonieee (for example), using the existing libgcc functions.  
Appropriate arrangements are made for when one libm function calls another 
so that the _nonieee functions call other _nonieee functions.

* cbrtl at existing symbol version is compat symbol alias for 
__cbrtl_nonieee.

* cbrtl at new symbol version uses -mieee libgcc functions.

* -mieee defines __IBM_LDOUBLE_IEEE__.  A powerpc-specific bits/*.h header 
redirects cbrtl to __cbrtl_nonieee unless __IBM_LDOUBLE_IEEE__ is defined.  
(So uses of -mieee get the new cbrtl, people not using it (unless they 
declare functions themselves rather than using headers) and existing 
binaries get __cbrtl_nonieee.  As long as library headers are used, this 
would make the glibc default match the GCC default.)

To be clear, I'm not offering to implement that, only the GCC changes to 
add -mieee and the new libgcc functions and the associated glibc change to 
build with -mieee; anyone wanting to make the glibc default match the GCC 
default would need to follow up with changes such as the above.  But I 
think the above would be better than trying to keep marking failures 
expected when they arise from libgcc problems.

-- 
Joseph S. Myers
joseph@codesourcery.com


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