Speed test on power of two

powerOfTwo.js

// TEST A

function isPowerA ( x ) {
	while ( ( ( x % 2 ) === 0 ) && x > 1 ) x /= 2;
	return ( x === 1 );
}

var i = 10000000;

while ( i > 0 ) {
	isPowerA( 2048 );
	i--;
}
// result: Approx 218 ms


// TEST B

function isPowerB ( x ) {
	return ( x && !( x & ( x - 1 ) ) );
}

var i = 10000000;

while ( i > 0 ) {
	isPowerB( 2048 );
	i--;
}
// result: Approx 66 ms


// TEST C

function isPowerC ( x ) {
	return ( ( x & ~15 ) === x );
}

var i = 10000000;

while ( i > 0 ) {
	isPowerC( 2048 );
	i--;
}
// result: Approx: 68 ms

Unit test on "is power of two?" check