Date: Sat, 7 May 2011 23:19:14 +0200 From: Stefan Bethke <stb@lassitu.de> To: Andriy Gapon <avg@FreeBSD.org> Cc: Kostik Belousov <kostikbel@gmail.com>, current@FreeBSD.org Subject: Re: bitcount32: replace lengthy comment with SWAR reference Message-ID: <4A9DD4AC-94CF-4AA5-AB17-8597CB6EB394@lassitu.de> In-Reply-To: <4DC5B2A4.60603@FreeBSD.org> References: <4DC517B3.8050502@FreeBSD.org> <20110507104748.GL48734@deviant.kiev.zoral.com.ua> <AEBDC7CF-CB63-41E7-8F1A-33DC0A6F7C8F@lassitu.de> <4DC5B2A4.60603@FreeBSD.org>
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Am 07.05.2011 um 22:59 schrieb Andriy Gapon: > on 07/05/2011 23:22 Stefan Bethke said the following: >> >> Am 07.05.2011 um 12:47 schrieb Kostik Belousov: >> >>> On Sat, May 07, 2011 at 12:58:11PM +0300, Andriy Gapon wrote: >>>> >>>> I think that the SWAR reference should be more concise and should lead an >>>> interested reader to more information on the topic (and more up-to-date as well). >>>> >>> SWAR acronim seems to be a wikipedia invention. Without the abbreviation, >>> the trimmed down comment looks better, IMHO. >> >> How about a proper reference, for example Warren's Hackers Delight (p. 65)? > > Hm, what makes that reference proper or more (most) proper? > My top google results for SWAR seem to point to materials created by inventors > of the algorithm. Your google-fu is clearly superior. It took me a couple tries to find the page you're refering to. http://aggregate.org/MAGIC/#Population%20Count%20%28Ones%20Count%29 Why not put a link in there directly? I just prefer a reference I can actually look up over an acronym that (by itself) cannot easily be resolved. The algorithm itself seems to predate SWAR significantly: according to Hackers Delight, it was described in /Combinatorial Algorithms: Theory and Pratice/ in 77. The code in systm.h appears to be a slightly less optimized version of the algorithm presented in SWAR or Hacker's Delight. Stefan -- Stefan Bethke <stb@lassitu.de> Fon +49 151 14070811
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