phc-discussions - Re: [PHC] yescrypt on GPU

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Message-ID: <20151011062945.GA11179@openwall.com>
Date: Sun, 11 Oct 2015 09:29:45 +0300
From: Solar Designer <solar@...nwall.com>
To: Massimo Del Zotto <massimodz8@...il.com>
Cc: discussions@...sword-hashing.net
Subject: Re: [PHC] yescrypt on GPU

Massimo,

As a trivial change to your existing code, you could try moving the
barrier.  You have:

				barrier(CLK_LOCAL_MEM_FENCE);
			}
			xo = (ulong)(xo >> 32) * (uint)xo;
			xo += gather[0 + 0];
			xo ^= gather[2 + 0]; // do this uint for slightly improved perf?
			xi = (ulong)(xi >> 32) * (uint)xi;
			xi += gather[0 + 1];
			xi ^= gather[2 + 1];

but you could have:

			xo = (ulong)(xo >> 32) * (uint)xo;
			xi = (ulong)(xi >> 32) * (uint)xi;
			barrier(CLK_LOCAL_MEM_FENCE);
			xo += gather[0 + 0];
			xo ^= gather[2 + 0]; // do this uint for slightly improved perf?
			xi += gather[0 + 1];
			xi ^= gather[2 + 1];

Maybe the compiler does this for you anyway, or maybe not.

The way I designed pwxform, the multiplications and gather loads are
supposed to work in parallel.

Alexander