This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Bad choices by expand_mult_highpart


Richard Sandiford wrote:

> This suggests there are more things that choose_mult_variant/synth_mult
> ought to try, such as getting rid of leading 1s before dealing with the
> lower bits.  OTOH, given my recent record, I've very little confidence
> I'd get something like that right.

Isn't this really a well-known problem ("addition chains") where
optimal algorithms have been found?  Look e.g. at how powi is handled 
in builtins.c.

> So, patch withdrawn.  I'll try to stop wasting everyone's time
> and embarrassing myself further. ;(

Never mind ;-)

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]