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Message-ID: <20130729011109.GA4458@openwall.com>
Date: Mon, 29 Jul 2013 05:11:09 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: bcrypt
Katja -
On Mon, Jul 29, 2013 at 05:07:03AM +0400, Solar Designer wrote:
> On Mon, Jul 29, 2013 at 02:04:06AM +0200, Katja Malvoni wrote:
> > [...] I need a way to preload P arrays in
> > assembly and implementing whole loop in assembly was my only idea.
>
> When you're still using gcc's inline asm, would you be able to declare
> those 36 registers as clobbered? I thought you mentioned a list of 30
> regs specified in the asm statement - does this apply to clobbered regs
> as well? If you can't specify all 36, then with inline asm you'd be
> stuck between suboptimal code (preloading fewer than all 36 elements)
> and unreliable code (which may break with any recompile in a slightly
> different environment). So this would be yet another reason for you to
> move to using a separate assembly source file.
Oh, you would have a third option here, although it's also suboptimal:
preload all 36 regs, but for those you could not declare as being
clobbered you'd have to manually save/restore them from an array in
local memory (you'd have to do that regardless of whether the regs were
actually in use for something else in a given build or not, since your
code would not know that). Actually, this is not more suboptimal than a
separate assembly file would be, where you'd also have to save/restore
all callee-saved registers that you use, regardless of whether the
caller actually depends on that or not...
Alexander
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