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Date: Thu, 27 Jun 2013 11:35:05 -0400
From: Yaniv Sapir <yaniv@...pteva.com>
To: john-dev@...ts.openwall.com
Subject: Re: Parallella: bcrypt
FWIW, looking at the disassembly, it seems like the loop there spans over
~50 instructions, which means that it takes the order of magnitude of 50
cycles (probably some stalls due to dependency are balanced with
instruction multi-issue). If this is right, then unrolling the loop further
will add marginal gain - as the branch penalty is 4-5 cycles.
On Thu, Jun 27, 2013 at 11:15 AM, Solar Designer <solar@...nwall.com> wrote:
> Katja,
>
> On Thu, Jun 27, 2013 at 04:54:31PM +0200, Katja Malvoni wrote:
> > 26c: 905f 4806 lsl r20,r20,0x2
> > 270: 2456 lsl r1,r1,0x2
>
> We should be able to avoid needing these instructions if you pick the
> version of the BF_ROUND macro that's intended for archs without scaled
> index on loads. The crypt_blowfish.c file in musl doesn't include it,
> so you'll need to take it from our separate crypt_blowfish distribution.
>
> In fact, here it is:
>
> /* Architectures with no complicated addressing modes supported */
> #define BF_INDEX(S, i) \
> (*((BF_word *)(((unsigned char *)S) + (i))))
> #define BF_ROUND(L, R, N) \
> tmp1 = L & 0xFF; \
> tmp1 <<= 2; \
> tmp2 = L >> 6; \
> tmp2 &= 0x3FC; \
> tmp3 = L >> 14; \
> tmp3 &= 0x3FC; \
> tmp4 = L >> 22; \
> tmp4 &= 0x3FC; \
> tmp1 = BF_INDEX(data.ctx.S[3], tmp1); \
> tmp2 = BF_INDEX(data.ctx.S[2], tmp2); \
> tmp3 = BF_INDEX(data.ctx.S[1], tmp3); \
> tmp3 += BF_INDEX(data.ctx.S[0], tmp4); \
> tmp3 ^= tmp2; \
> R ^= data.ctx.P[N + 1]; \
> tmp3 += tmp1; \
> R ^= tmp3;
>
> Another optimization to try is unrolling more rounds. The loop in
> musl's BF_encrypt() unrolls only two rounds, but it has that "#if 0"
> block with all 16 unrolled - would the code still fit if you change it
> to "#if 1"? Perhaps it would.
>
> Alexander
>
--
===========================================================
Yaniv Sapir
Adapteva Inc.
1666 Massachusetts Ave, Suite 14
Lexington, MA 02420
Phone: (781)-328-0513 (x104)
Email: yaniv@...pteva.com
Web: www.adapteva.com
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