how to find a number whether its a power of 2 or not

[MJ]

Hi
I have question about the C.
I have a number X which is power of two
X = 2 power n
I need to find it using a Single C statement whether its a power of 2
or not
I know that a number with power of 2 will have only one single bit as 1
and rest of the bit as 0. To check the bit I need to go through all the
bits ones and check for the condition. I dont want use a loop. In that
case how can I do this

Thanks in advance
Regards
Mayur...

[Walter Roberson]

In article <11**********************@g14g2000cwa.googlegroups .com>,
MJ <ma********@gmail.com> wrote:

I have question about the C.
I have a number X which is power of two
X = 2 power n
I need to find it using a Single C statement whether its a power of 2
or not

This question seems to get asked every couple of weeks.

Consider this: if X is a power of 2, then (X-1) differs from X
in all the bit positions (other than the leading 0's).
--
'The short version of what Walter said is "You have asked a question
which has no useful answer, please reconsider the nature of the
problem you wish to solve".' -- Tony Mantler

[Martijn]

> X = 2 power n

I need to find it using a Single C statement whether its a power of 2
or not

http://www.catch22.net/source/snippets.asp

Top of the page

--
Martijn
http://www.sereneconcepts.nl

[Kenny McCormack]

In article <11**********************@g14g2000cwa.googlegroups .com>,
MJ <ma********@gmail.com> wrote:

Hi
I have question about the C.
I have a number X which is power of two
X = 2 power n
I need to find it using a Single C statement whether its a power of 2
or not

The answer is "Yes".

(In your problem statement, you state that X is a power of two)

[Richard Bos]

"MJ" <ma********@gmail.com> wrote:

I need to find it using a Single C statement whether its a power of 2
or not

If you need to use a single statement, it's not a real problem, it's
homework. So consider _why_ you've been given this homework... would
that be to learn something about copying code from a newsgroup? I think
not.

Richard

[Gregory Pietsch]

unsigned int is_power_of_2(unsigned int x)
{
return (x != 0) && ((x & (x - 1)) == 0);
}

/* Gregory Pietsch */

[pete]

MJ wrote:

Hi
I have question about the C.
I have a number X which is power of two
X = 2 power n
I need to find it using a Single C statement whether its a power of 2
or not
I know that a number with power of 2 will
have only one single bit as 1 and rest of the bit as 0.
To check the bit I need to go through all the
bits ones and check for the condition. I dont want use a loop. In that
case how can I do this

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1) && n % 1 == 1;
}

int n_is_Power_of_four(unsigned n)
{
return !(n & n - 1) && n % 3 == 1;
}

int n_is_Power_of_eight(unsigned n)
{
return !(n & n - 1) && n % 7 == 1;
}

--
pete

[Peter Nilsson]

pete wrote:

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1) && n % 1 == 1;
}

For what unsigned n is n % 1 == 1? ;)

--
Peter

[pete]

Peter Nilsson wrote:

pete wrote:

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1) && n % 1 == 1;
}

For what unsigned n is n % 1 == 1? ;)

It's part of the sequence:
return !(n & n - 1) && n % 1 == 1
return !(n & n - 1) && n % 3 == 1
return !(n & n - 1) && n % 7 == 1

--
pete

[pete]

pete wrote:

Peter Nilsson wrote:

pete wrote:

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1) && n % 1 == 1;
}

For what unsigned n is n % 1 == 1? ;)

It's part of the sequence:
return !(n & n - 1) && n % 1 == 1
return !(n & n - 1) && n % 3 == 1
return !(n & n - 1) && n % 7 == 1

However, it seems to be completely wrong. Thank you.

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1);
}

--
pete

[Jonathan Adams]

In article <42***********@mindspring.com>,
pete <pf*****@mindspring.com> wrote:

pete wrote:

Peter Nilsson wrote:

pete wrote:
> int n_is_Power_of_two(unsigned n)
> {
> return !(n & n - 1) && n % 1 == 1;
> }

For what unsigned n is n % 1 == 1? ;)

It's part of the sequence:
return !(n & n - 1) && n % 1 == 1
return !(n & n - 1) && n % 3 == 1
return !(n & n - 1) && n % 7 == 1

However, it seems to be completely wrong. Thank you.

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1);
}

Is 0 a power of two, then?

- jonathan

[pete]

Jonathan Adams wrote:

In article <42***********@mindspring.com>,
pete <pf*****@mindspring.com> wrote:

pete wrote:

Peter Nilsson wrote:
>
> pete wrote:
> > int n_is_Power_of_two(unsigned n)
> > {
> > return !(n & n - 1) && n % 1 == 1;
> > }
>
> For what unsigned n is n % 1 == 1? ;)

It's part of the sequence:
return !(n & n - 1) && n % 1 == 1
return !(n & n - 1) && n % 3 == 1
return !(n & n - 1) && n % 7 == 1

However, it seems to be completely wrong. Thank you.

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1);
}

Is 0 a power of two, then?

Not really. Thank you.

int n_is_Power_of_two(unsigned n)
{
return !(n & n - 1) && n != 0;
}

--
pete