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Date: Wed, 17 Jul 2013 19:40:17 +0200
From: Katja Malvoni <kmalvoni@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: bcrypt

On Wed, Jul 17, 2013 at 7:17 PM, Katja Malvoni <kmalvoni@...il.com> wrote:

> [..]
>
> This is good news, but I suspect there was some error in your
>> measurements, or if no error then we don't know why the computation
>> prior to the main loop is taking 2.5 ms.  This 2.5 ms is excessive
>> (should be several times less than that).  I suspect that you measured
>> communication time as part of it, or maybe it's so slow because it
>> involves reads from off-chip memory?
>>
>
> I was surprised by that as well, I measured it again, 2.5 ms. I'm
> measuring clock ticks with Epiphany timers (assuming 600 MHz), I start
> timer after declarations in BF_crypt and I stop it before entering do{ ...
> }while(--count);
> I was passing pointers to shared buffer when calling BF_crypt(), I tried
> copying data from shared buffer into local variables, it's even slower -
> 809 c/s
>
>

It comes from copying initial S box to data structure in BF_crypt() (takes
around 2.3 ms). If S box is not copied than it must be transferred before
each BF_crypt call. Initial S box is transferred when loading *.srec file.
I think this is cheaper than transferring it from host to Epiphany per
every computed hash.

Katja

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