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Date: Tue, 10 Jul 2012 08:20:23 +0530
From: Sayantan Datta <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: Rotate and bitselect investigation

On Tue, Jul 10, 2012 at 8:05 AM, Solar Designer <solar@...nwall.com> wrote:

> Sayantan, magnum -
>
> On Tue, Jul 10, 2012 at 07:19:38AM +0530, Sayantan Datta wrote:
> > On Tue, Jul 10, 2012 at 7:00 AM, Solar Designer <solar@...nwall.com>
> wrote:
> > > Maybe we should use the same approach that magnum uses in
> rar_kernel.cl:
> > >
> > > #ifdef cl_nv_pragma_unroll
> > > #define NVIDIA
> > > #endif
> > > [...]
> > > #ifdef NVIDIA
> > > #define F(x,y,z)        (z ^ (x & (y ^ z)))
> > > #else
> > > #define F(x,y,z)        bitselect(z, y, x)
> > > #endif
> > >
> > > This won't detect CPUs, though - where we also don't want to use
> > > bitselect() most of the time (the instruction is only available with
> XOP
> > > and is probably not used by current OpenCL SDKs since I think only
> > > Intel's does vectorization) - but this code is mostly just for AMD and
> > > NVIDIA GPUs now.  We have faster MSCash2 code on CPU anyway.
>
> > So we should use manual bitselect by default.
>
> But we don't have a trick similar to cl_nv_pragma_unroll that would let
> us detect AMD GPUs.  So I am fine with us using bitselect() by default
> and only disabling it on NVIDIA, unless/until we learn of a trick to
> detect AMD GPU in OpenCL (or introduce such way by passing the info from
> our C code).
>
> Alexander
>

That is great. I overlooked #ifdef cl_nv_pragma_unroll. I'll make the
changes ASAP.

Regards,
Sayantan

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