IS_POWER_OF_TWO macro

Power of two numbers means that 2 multiplied by itself multiple times to produce another number (power of two numbers). 1 is also power of two numbers when 2 is multiplied to itself 0 time (zeroth power of 2 - don't ask me why :P).

Check if a number is power of two using macro defined function:

#define IS_POWER_OF_TWO(x) ( !( (x) & ((x)-1) ) )

e.g.
i. 4 is power of 2 (2x2)
4 == 0000 0100 binary
4-1 = 3 == 0000 0011 binary
ANDED == 0000 0000
! == 1111 1111 == is a power of two

ii. 8 is power of 2 (2x2x2)
8 == 0000 1000 binary
8-1 = 7 == 0000 0100 binary
ANDED == 0000 0000
! == 1111 1111 == is a power of two

iii. 15 is NOT power of 2 ( 2x2x2 == 8, 2x2x2x2 == 16 which already passed 15)

15 == 0000 1111 binary
15-1 = 14 == 0000 1110 binary
ANDED == 0000 1110 ( ! will result 0 )
! == 0000 0000 == not a power of two number

e.g C codes

#include
#include

#define ISPOW2(x)
!((x)&((x-1)))

int main (int argc, char *argv[])
{
int i=0;
int res=0;

if ( argc < face="courier new" size="2">
{
printf("Not enough input arguments\n");

return -1;
}

i = atoi(argv[1]);

if ( (res=ISPOW2(i)) )
printf("Number %d is a power of 2.\n", i);
else
printf("Number %d is NOT a power of 2.\n", i);

printf ("res = %d\n", res);

return 0;
}