Re: [RFC][PATCH] New expf, exp2f, logf, log2f and powf implementations

[Corinna Vinschen <vinschen at redhat dot com>]

Hi Szabolcs,

On Aug 30 15:18, Szabolcs Nagy wrote:
> Based on code from https://github.com/ARM-software/optimized-routines/
> 
> This patch adds a highly optimized generic implementation of expf,
> exp2f, logf, log2f and powf.  The new functions are not only
> significantly faster, but are also smaller, more accurate and fix
> several correctness issues.  In order to achieve this, the algorithm
> uses double precision arithmetic for accuracy, avoids divisions and
> uses small table lookups to minimize the polynomials.  Special cases
> are handled inline to avoid the unnecessary overhead of wrapper
> functions and set errno to POSIX requirements.
> 
> The new functions are added under newlib/libm/common and are
> currently enabled for AArch64 and AArch32 with VFP format.  The
> new functions are written in C99 and do not support non-IEEE
> representations, mixed endian doubles or non-standard errno setting.
> Targets can enable the new math code by undefining OBSOLETE_MATH.
> Targets with a single precision FPU may still prefer the old
> implementation. It was not clear what's the best way to add such
> alternative math implementations to newlib so this is an RFC
> patch and feedback is welcome.

I'm not confident enough with math stuff to review this, so I'd
rather like to defer to Jeff here.

However, two points:

- Please send the patch as generated by `git format-patch'.  Ideally
  as a patchset of smaller patches.

- Why the OBSOLETE_MATH stuff?  If these implementations are generic
  and sufficiently tested, wouldn't it make sense to enable them by
  default without forcing other targets to enable the OBSOLETE_MATH
  setting?


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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