Date: Sun, 22 Aug 1999 09:14:26 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: hibma@skylink.it Cc: hackers@FreeBSD.ORG Subject: Re: from number to power of two Message-ID: <199908221314.JAA18225@hda.hda.com> In-Reply-To: <Pine.BSF.4.10.9908220956450.7595-100000@heidi.plazza.it> from Nick Hibma at "Aug 22, 99 10:00:35 am"
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> It seems that all the solutions are too generic and slow. As I only have > to check the numbers 0-32 (actually 1-32), a block of if statements is > almost as fast as a table look up in 33 elements. I doubt it - use the table for a small fixed size set then use Warner's "(n) ? (1 << (ffs(n) - 1)) : 0". The possible inline ffs is in machine/cpufunc.h ffs() is fundamental to scheduling queues and cryptography and should have attention paid to it. As Warner said, it could be a single instruction on some architectures. Peter -- Peter Dufault (dufault@hda.com) Realtime development, Machine control, HD Associates, Inc. Safety critical systems, Agency approval To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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