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Message-ID: <20130725154536.GA15210@openwall.com>
Date: Thu, 25 Jul 2013 19:45:36 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: bcrypt
Yaniv -
On Thu, Jul 25, 2013 at 07:35:58PM +0400, Solar Designer wrote:
> Yaniv - which is better: IMUL followed by simple LDR (no index) or IMADD
> followed by LDR with index?
Oops, I got this question backwards. Let me try again:
Which is better: IMADD followed by simple LDR (no index), or IMUL
followed by LDR with index?
> In other words, is it better to use the
> adder on the FPU or the adder in the IALU for our address calculation,
> when we have the choice to use either? I think the code will run at the
> same speed either way, but maybe there's a difference in power usage and
> heat production by the chip?
This part of the question was/is correct.
Basically, we'd use the FPU for index scaling either way (since IALU
lacks the capability), but we have the choice to use either FPU or IALU
for adding the scaled index to the base address.
Alexander
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