phc-discussions - Re: [PHC] Supporting AVX2/SSE2 or not with a single binary

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Message-ID: <532A40A9.9090501@dei.uc.pt>
Date: Thu, 20 Mar 2014 01:13:13 +0000
From: Samuel Neves <sneves@....uc.pt>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Supporting AVX2/SSE2 or not with a single binary

On 20-03-2014 00:54, Bill Cox wrote:
> One reason I think we see applications running without SSE/AVX2
> support is that operating systems don't want to support two versions
> of a binary, and they have to support older machines.  The Blake2 code
> I've read does not provide for a single binary that supports both - I
> have to link either to the blake2-ref code or the blake2-sse code.  My
> TwoCats code has inherited this limitation, since I used the Blake2
> code as a roadmap for figuring out how SSE2 works.

libb2 [1] does have basic support for runtime CPU feature detection. In
general, though, this is annoying to support in a portable way due to
different ways to invoke cpuid between compilers, operating system
support (you may have an AVX-capable system but the OS may not save ymm
registers across context switches), and so on.

[1] https://blake2.net/#dl