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Date: Tue, 30 Jun 2015 13:51:17 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH v2 5/6] dynlink.c: compute modulus via magic
 multiplication

On Sun, Jun 28, 2015 at 02:48:34AM +0300, Alexander Monakov wrote:
> Based on http://ridiculousfish.com/blog/posts/labor-of-division-episode-iii.html
> 
> Do a little hand-holding for the compiler and fold magic post-shift into
> 32-bit high word -> low word shift on 64-bit platforms.
> ---

On 32-bit Atom, I was able to get an improvement from 116ms to 113ms
running an empty program linked with a .so produced using the attached
script. This is probably roughly best-case improvement, so the umod
stuff is probably not likely to be worthwhile unless/until we can
improve the areas that are currently dominating the runtime. That's
rather disappointing, but maybe we can improve enough other stuff for
it to make sense to do the umod optimization.

Rich

Download attachment "gen.sh" of type "application/x-sh" (104 bytes)

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