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Date: Sun, 16 Aug 2015 16:30:23 +0200
From: Agnieszka Bielec <bielecagnieszka8@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: PHC: Argon2 on GPU
2015-08-16 16:09 GMT+02:00 Solar Designer <solar@...nwall.com>:
> On Sun, Aug 16, 2015 at 03:03:56PM +0200, Agnieszka Bielec wrote:
>> 2015-08-16 14:48 GMT+02:00 Solar Designer <solar@...nwall.com>:
>> > On Sun, Aug 16, 2015 at 02:01:38PM +0200, Agnieszka Bielec wrote:
>> >> prev_block[i] = ((__global ulong2*)memory)[bi+i];
>> >> }
>> >>
>> >> see anyone some logic here or is this just a bug on AMD?
>> >
>> > Why do you call this a bug? It isn't necessarily a bug when performance
>> > of code changes when you change the source code.
>> >
>> > Anyway, it looks like in the second code version you rely on address
>> > scaling by 16, and this is probably not available in the architecture
>> > (usually available is scaling by up to 8), so requires extra
>> > instructions (explicit left shifts).
>>
>> where do you see address scaling?
>
> bi+i is used to index an array if 16-byte elements, so it needs to be
> multiplied by 16 each time (unless the compiler manages to optimize
> this, perhaps much like you had done manually in the first version).
ok
>> bi is uint and even before /16 is
>> BLOCK_SIZE which is much bigger than 16 and divisible by 16 so
>
> How is this relevant?
>
>> preprocessor will change this to *[single value]
>
> I don't see any preprocessor macros here, on the line I quoted above.
not relevant anymore
> What branch is this committed on, so that I can take a look in context?
bleeding-jumbo
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