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Date: Tue, 7 Jul 2015 00:24:47 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: extend SIMD intrinsics
On Mon, Jul 06, 2015 at 08:08:21PM +0200, magnum wrote:
> On 2015-07-06 10:23, Solar Designer wrote:
> >Regarding possible use of union types, here's a relevant posting by
> >Alexander Cherepanov:
> >
> >http://article.gmane.org/gmane.comp.security.phc/2753
> >
> >Nearby postings in this thread are also relevant.
>
> I get more depressed the more I read.
Indeed.
> + typedef union {
> + vtype v;
> + uint32_t s[SIMD_COEF_32];
> + } vtype32;
>
> + typedef union {
> + vtype v;
> + uint64_t s[SIMD_COEF_64];
> + } vtype64;
Disregarding the unclear status of arrays within unions as it relates to
strict aliasing rules, this is what I would suggest too.
This is probably the most reasonable approach for us now.
Why two separate union types, though? We could use a shared type, with
two arrays in place of s. Would have to call those e.g. s32 and s64.
> - void SSESHA1body(vtype* _data, ARCH_WORD_32 *out, ARCH_WORD_32
> *reload_state, unsigned SSEi_flags)
> + void SSESHA1body(vtype32 *data, vtype32 *out, vtype32 *reload_state,
> uint32_t SSEi_flags)
> {
> ...
> vtype a[SIMD_PARA_SHA1];
> vtype b[SIMD_PARA_SHA1];
> ...
> SHA1_PARA_DO(i)
> {
> - a[i] = vload((vtype*)&reload_state[i*16*VS32+0*VS32]);
> + a[i] = vload(reload_state->v[i*16+0]);
> ...
Why not simply:
a[i] = reload_state->v[i*16+0];
or why not simply use reload_state->v[i*16+0] in a subsequent expression
in place of a[i]? I think use of a[i] may only be needed when we start
doing computation, not for the load.
> Would this take us forward or back?
Forward, I hope.
Using those union types inside SSESHA1body(), etc. would be even safer,
so e.g.:
vtype32 a[SIMD_PARA_SHA1];
vtype32 b[SIMD_PARA_SHA1];
[...]
a[i].v = reload_state->v[i*16+0];
but it increases our reliance on the optimizer for producing fast code.
Alexander
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