phc-discussions - Re: [PHC] Question about saturating the memory bandwidth

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Date: Sat, 18 Jan 2014 14:51:23 -0500
From: Bill Cox <waywardgeek@...il.com>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Question about saturating the memory bandwidth

On Sat, Jan 18, 2014 at 9:16 AM, Solar Designer <solar@...nwall.com> wrote:
> Another option is making use of a larger "ROM" (multi-gigabyte).  As I
> had mentioned, for busier-than-in-example-above dedicated authentication
> servers, we're currently playing with parameters that give
> 7300 req/s/machine on a large(r) machine, using 112 GiB ROM (= 120 GB) +
> 1.75 MiB RAM/instance.

Awesome.  I just ran this code in my Chrome browser in 1.4 seconds:

memhash = function(m) {
    var hash = m;
    var v = new Array();
    v[0] = hash;
    var memlen = 10000000;
    for (var i = 1; i < memlen-1; i++) {
        hash = (hash*(v[i >> 1] | 1) + 12345) % (1 << 30);
        v[i] = hash;
    }
    return v[hash % memlen];
}

writeln(1 << 30)
writeln(memhash(45));

I think it writes 40MB, and reads 20MB.  Maybe twice that if it is
storing 64-bit floats.  I think this shows we can probably allow users
to perform hashing in their browsers, offloading the servers.  For
clients without javascript, just do it on the server, but that's a big
offload.  This even works on PHP backed servers with no native code
access.

Bill