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Message-ID: <CAAepdCZLTH4mF=jpV2rAtyLc-f_FqA7vgDSe_ZLDjcqXYS20Aw@mail.gmail.com>
Date: Thu, 22 Aug 2013 22:26:19 +0100
From: Rafael Waldo Delgado Doblas <lord.rafa@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: Litecoin mining
Hello,
2013/8/22 Solar Designer <solar@...nwall.com>
> How is your SCRATCHBUF_SIZE calculated? You have:
>
> // ((1023 / TMTO_RATIO) + 1) * 128
>
> #define SCRATCHBUF_SIZE 22464
> #define TMTO_RATIO 6 // Must be > 0
>
> However, when I substitute 6 into the formula in the comment, I get only
> 21888, not 22464. Is the 22464 number right, and why? Can you please
> edit this file so that SCRATCHBUF_SIZE uses a formula rather than a
> constant on the #define line? For example:
>
> #define TMTO_RATIO 6
> #define SCRATCHBUF_SIZE (((1023 / TMTO_RATIO) + 1) * 128)
>
> (if that formula is right). Any decent optimizing compiler will compute
> this at compile time anyway.
>
Well this formula works fine the (512+64) are for B and X in the original
code but since these vectors are no longer inside of SCRATCHBUF,
SCRATCHBUF can be decreased safely.
> The code in scrypt_1024_1_1_256_sp() adds 64-byte alignment, so may
> waste up to 63 bytes. If you do implement any alignment like this, then
> you need to account for it (worse case) in SCRATCHBUF_SIZE. However,
> please note that, unlike systems with cache, Epiphany does not benefit
> from larger than 8-byte alignment (and it only benefits from 8-byte
> alignment if your code manages to use LDRD/STRD instructions, otherwise
> it only needs 4-byte alignment). Thus, I suggest that you drop the line
> that implements alignment manually and don't include it in
> SCRATCHBUF_SIZE either, but instead define scratchpad like this:
>
> char scratchpad[SCRATCHBUF_SIZE] __attribute__ ((aligned (8)));
>
> then you can do simply:
>
> V = (uint32_t *)scratchpad;
>
> ... or arguably it may be cleaner to use:
>
> uint32_t scratchpad[SCRATCHBUF_SIZE / 4] __attribute__ ((aligned
> (8)));
>
> and then:
>
> V = scratchpad;
>
> "__attribute__ ((aligned (8)))" is gcc-specific, but we assume e-gcc for
> the Epiphany code anyway. (If we were writing more portable code, we
> could use a "union" with a "long long" or a "double" inside it to
> achieve 8-byte alignment.)
>
Ok, I will do that.
Regards,
Rafael
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