[LLVMdev] Mul & div support for wider-than-legal types

[Paweł Bylica]

Can it be a first step?
http://reviews.llvm.org/D8770

- Paweł

On Sun, Mar 22, 2015 at 5:35 PM Joerg Sonnenberger <joerg at britannica.bec.de>
wrote:

> On Sun, Mar 22, 2015 at 03:18:14PM +0000, Paweł Bylica wrote:
> > On Sun, Mar 22, 2015 at 5:57 AM Joerg Sonnenberger <
> joerg at britannica.bec.de>
> > wrote:
> >
> > > On Fri, Mar 20, 2015 at 08:06:11PM -0700, Tim Northover wrote:
> > > > > mul can be inlined easily if necessary for arbitrary sizes, but
> div is
> > > very expensive.
> > > >
> > > > Shall I file a bug for "implement FFT in LLVM"?
> > >
> > > I didn't say it is the most efficient algorithm :) That's why I asked
> > > about the purpose.
> > >
> > > Joerg
> > >
> >
> >  Can you suggest an algorithm and implementation then?
>
> For short multi-word multiplications, school book approach works fine.
> For medium sizes problems, Karatsuba or Toom-Cook is better. For truely
> larger problems, it boils down to FFT. Of course, all this needs careful
> benchmarking if you want to select a specific one.
>
> Joerg
>
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