NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/3292

Internet Message Format | 1996-08-05 | 1.3 KB

Path: Rezonet.net!news
From: [e-mail] (Ray Dunn)
Newsgroups: comp.lang.c
Subject: Re: quick decision: is n a power of 2?
Date: 25 Jan 1996 16:24:50 GMT
Organization: Ultimate Technographics Inc.
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In referenced article, Lawrence Kirby says...
>>int is_power_of_two(int k) {       /* 1.0  1.0  1.0  1.0 */
>>   if (k <= 0) return 0;
>>   return (!(k & (k-1)));
>>}
>>
>>int is_power_of_two(int k) {       /*  1.1  1.0  1.1  1.0 */
>>   if (k <= 0) return 0;
>>   return ((k & (k-1))  == 0);
>>}
>
>I wouldn't be too impressed these days with a compiler that generates
>less efficient code for ((k & (k-1) == 0) than (!(k & (k-1))

Yes, that was my reaction too, but looking at it, the differences are
in the noise level for this sort of timing which usually varies quite a
bit - especially when using a test that only runs for 1 second.
--
Ray Dunn (opinions are my own) | Phone: [phone]
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