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Date: Mon, 3 Aug 2015 05:58:53 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: JtR on ARM (NEON)

On Mon, Aug 03, 2015 at 04:39:38AM +0200, magnum wrote:
> On 2015-07-31 10:35, Solar Designer wrote:
> >>From the figures above, MD4 and MD5 get 2x speedup; SHA1 and SHA256
> >>have no speedup; SHA512 gets a lot slower.
> >
> >Yes.  That's weird(...) Maybe unaligned accesses.
> 
> How slow is NEON with unaligned scalar 32-bit? The raw formats' 
> set_key() read the key (which may be unaligned) using 32-bit loads and 
> places directly in the SIMD buffer. It might be a coincidence that 
> MD4/MD5 happens to get aligned test vector keys and the others doesn't. 
> Other than that I can't see what would be unaligned.

I think we must not have any unaligned accesses on ARM at all.  If we
currently do have any, let's fix that as a bug.

While not completely unsupported, they are tricky:

"How does the ARM Compiler support unaligned accesses?"
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15414.html

http://www.heyrick.co.uk/armwiki/Unaligned_data_access

Alexander

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