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From: Nomen Nescio on 7 Mar 2010 06:40
http://www.das-labor.org/wiki/AVR-Crypto-Lib/en

I was stunned to see that the ASM (assembler) implementation of AES is
more than ten times (!) as fast as the C implementation. I'd have
thought that compiler technology had narrowed the difference to maybe
10-20%. The compiler is probably GCC-AVR, which isn't as advanced as
say, the Microsoft compilers, but the difference is remarkable.

From: Tom St Denis on 7 Mar 2010 07:25
On Mar 7, 6:40 am, Nomen Nescio <nob...(a)dizum.com> wrote:
> http://www.das-labor.org/wiki/AVR-Crypto-Lib/en
>
> I was stunned to see that the ASM (assembler) implementation of AES is
> more than ten times (!) as fast as the C implementation. I'd have
> thought that compiler technology had narrowed the difference to maybe
> 10-20%. The compiler is probably GCC-AVR, which isn't as advanced as
> say, the Microsoft compilers, but the difference is remarkable.

Say what? GCC on x86 *is* more advanced than MSVC by a long shot.
Most lilkely though GCC for AVR isn't 100%. Just like GCC for ARM is
not as good as ARM's own compiler.

It's not uncommon to see assembler based AES 2-3 times faster than C.
It shouldn't be 10x though...
From: Tom St Denis on 7 Mar 2010 17:56
On Mar 7, 2:45 pm, henno <hennobrand...(a)gmail.com.invalid> wrote:
> Tom St Denis wrote:
> > On Mar 7, 6:40 am, Nomen Nescio <nob...(a)dizum.com> wrote:
> >>http://www.das-labor.org/wiki/AVR-Crypto-Lib/en
>
> >> I was stunned to see that the ASM (assembler) implementation of AES is
> >> more than ten times (!) as fast as the C implementation. I'd have
> >> thought that compiler technology had narrowed the difference to maybe
> >> 10-20%. The compiler is probably GCC-AVR, which isn't as advanced as
> >> say, the Microsoft compilers, but the difference is remarkable.
>
> > Say what?  GCC on x86 *is* more advanced than MSVC by a long shot.
> > Most lilkely though GCC for AVR isn't 100%.  Just like GCC for ARM is
> > not as good as ARM's own compiler.
>
> > It's not uncommon to see assembler based AES 2-3 times faster than C.
> > It shouldn't be 10x though...
>
> It could be if you used the new AES instructions in x64 chipset introduced in
> the i5 and i7 proecessors.

Strictly speaking I don't consider those comparable. Those
instructions are really just hardware offload of AES. It'd be like
having a mem mapped device sitting as a look-aside device.

Besides, strictly speaking there is no reason a C compiler can't also
use them. If it can determine that a function executes the AES ECB
decrypt/encrypt for instance it could just map it onto the relevent
functions :-)

Tom
From: Tom St Denis on 8 Mar 2010 09:11
On Mar 8, 7:45 am, Paulo Marques <pmarq...(a)grupopie.com> wrote:
> Nomen Nescio wrote:
> >http://www.das-labor.org/wiki/AVR-Crypto-Lib/en
>
> > I was stunned to see that the ASM (assembler) implementation of AES is
> > more than ten times (!) as fast as the C implementation. I'd have
> > thought that compiler technology had narrowed the difference to maybe
> > 10-20%. The compiler is probably GCC-AVR, which isn't as advanced as
> > say, the Microsoft compilers, but the difference is remarkable.
>
> The AVR is an 8-bit microcontroller that struggles to handle the 32 bit
> values that most AES implementations use.
>
> As an educated guess, the assembler implementation is probably able to
> use the 32 8-bit registers available to hold the internal state of the
> AES and even do some of the movement operations by simple register
> "renaming". In an AVR, a memory load or store operation takes 2 cycles.
> Avoiding them by using only registers is a major speed up.

True, keep in mind ATMEL did design a 32-bit AVR core as well. It's
very similar in IA to ARM [from what I recall], but it's also about 2x
slower [or less efficient, take your pick] than an ARM7 so ...

Tom
From: Noob on 8 Mar 2010 09:18
Tom St Denis wrote:

> True, keep in mind ATMEL did design a 32-bit AVR core as well. It's
> very similar in IA to ARM

What's IA? Did you mean ISA?
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