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From: "cosmos" <cosmos AT tvtel DOT pt>
To: <djgpp AT delorie DOT com>
References: <1116997063 DOT 905915 DOT 71670 AT z14g2000cwz DOT googlegroups DOT com> <d71i5h$t6h$1 AT nntp DOT fujitsu-siemens DOT com> <3E3le.7676$M36 DOT 381 AT newsread1 DOT news DOT atl DOT earthlink DOT net>
Subject: Re: to check given no. is power of 2
Date: Wed, 25 May 2005 20:27:30 +0100
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Reply-To: djgpp AT delorie DOT com

Hi,

Mathematically, a given number "N" is a power of 2 if "log(N) / log(2)" is
an integer, right? So:

#include <stdio.h>
#include <math.h>
  double param, fractpart, intpart;

  param = log(N) / log(2);
  fractpart = modf (param , &intpart);
  if (fracpart == 0)return 1; else return 0;Regards,Rui Fernandes


----- Original Message -----
From: "Martin Ambuhl" <mambuhl AT earthlink DOT net>
Newsgroups: comp.os.msdos.djgpp
To: <djgpp AT delorie DOT com>
Sent: Wednesday, May 25, 2005 7:39 PM
Subject: Re: to check given no. is power of 2


> Gerd Termathe wrote:
> > "aveo" <rahul DOT h AT gmail DOT com> schrieb im Newsbeitrag
> > news:1116997063 DOT 905915 DOT 71670 AT z14g2000cwz DOT googlegroups DOT com...
> >
> >>hi all
> >>i need a C code that checks given no. is power of 2 or not without
> >>checking any condition.
> >>
> >
> >
> > int is_power_of_2 (int N)
> > {
> >  if ( N!=0 && (N&(N-1))==0 ) return 1; else return 0;
> > }
>
> Why an if ... else?
> Why use uppercase for non-macros?
> Why use signed integers?
>
> inline unsigned is_power_of_2 (unsigned n)
> {
>    return (n && !(n&(n-1)));
> }
>