Date: Fri, 17 Apr 2015 03:05:32 +0300 From: Alexander Cherepanov <ch3root@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: Format interface changes On 2015-04-16 22:08, magnum wrote: > Solar, > > I think it may be about time we change key index/count variables to > unsigned int in Jumbo. Rationale: > > 1. The previously discussed need for GPU mask mode > http://www.openwall.com/lists/john-dev/2013/08/22/12 will soon show up > again. We'll soon need it. I don't really see a need for 64-bit pcount > though, just unsigned should be enough for a long time. > > 2. It makes things like "index/SIMD_COEF_32" that we have in wads of > SIMD calculations end up as a mere bitshift. The difference is quite > noticable, just changing NT2 and ignoring the compiler complaints render > a 4% boost. Before the recent AVX2 changes, we had it as > "(index>>(SIMD_COEF_32>>1))" but that only works for COEFs 2 and 4. For > a while we defined a SIMD_SHIFT_32 macro but I dropped it while fixing > all code for hardcoded widths (that was hard enough without it). Instead > of re-implementing it now, Sayantan's need came to mind. I'd really > prefer keeping the division in the source yet not in the compiled code! I guess this can easily be made with some macros but why bother? I generally agree that we should use unsigned more. I think it makes many things easier. It's great that you even have hard data on speed gain. Maybe change "char *ciphertext" to "unsigned char *ciphertext"? > Obviously we'll have to make some core code adopt to unsigned too. > > What do you think? BTW when we're at it, we could start using "const" > for pointer arguments where applicable - doing this at the same time > comes almost for free compared to doing it separately. I'll obviously do > most of it with grep/sed but there's always a substantial amount of > manual editing. Another couple of wild ideas: - add restrict to help compiler optimize code where we are sure that parameters cannot overlap. Many parameters are of type char * and I guess compiler cannot reason about its aliasing because char can be used to access any data; - is there need for parameters to be aligned? If many formats will benefit from this we can enforce it at the level of the interface. -- Alexander Cherepanov
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