phc-discussions - Re: [PHC] Compute time hardness

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Message-ID: <20150403121306.GA25444@openwall.com>
Date: Fri, 3 Apr 2015 15:13:06 +0300
From: Solar Designer <solar@...nwall.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Compute time hardness

Here's another relevant detail I recalled:

Pentium 4 (some or all of them? not sure) had double-pumped ALU, where
it could perform ADDs at double the clock rate (so up to 7.6 GHz, at
stock clocks).

http://www.anandtech.com/show/1611/7
http://forums.anandtech.com/showthread.php?t=603812
https://news.ycombinator.com/item?id=8255157
http://en.wikipedia.org/wiki/NetBurst_(microarchitecture)#Rapid_Execution_Engine

Apparently, this could only execute two dependent ADDs in a cycle if
they are 16-bit each.  To me, this indicates that an ASIC would probably
be able to do similar for 32-bit if it wanted to.

So I think this confirms 8x-ish difference in latency between fastest
ADD and MUL.

Alexander