phc-discussions - Re: [PHC] data-dependent branching (Re: [PHC] A little nit which bothers me...)

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Message-ID: <CAOLP8p5nvkEpTZDkmv+YLgTwqOEF0jgO9VM2E8uxgoAE9u-QuQ@mail.gmail.com>
Date: Wed, 2 Apr 2014 20:29:07 -0400
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] data-dependent branching (Re: [PHC] A little nit which
 bothers me...)

Data dependent branching doesn't seem to buy as much ASIC resistance
as some PHC submitters seem to think, IMO.  In an ASIC or FPGA, the
if-then-else statements synthesize to muxes in hardware, and then the
optimizer gets to reuse blocks that are in mutually exclusive block
statements.  For example, if there are four functions that have 32-bit
multiplies, the optimizer will put 4-to-1 muxes in front of it's
inputs, and reuse the multiplier for all 4 functions.  On the other
hand, there's not much that can be done to optimize data dependent
addressing.

Bill