NextHammingWeight - a function for finding the next int with the same hamming weight

NextHammingWeight

/* I was searching for an algorithm that gave you the next integer (counting
 * upwards) that has the same hamming weight as the current number, and I
 * couldn't find anything. So here's a function that does that for you. If
 * there is no 'next number' (i.e. this is the largest number that has this
 * hamming weight), it simply returns the same number again.
 * 
 * This can probably be optimized; I whipped it up pretty quickly. Relatedly, I
 * only tested a few edge cases I could think of, so if you use this, be sure
 * to test it more thoroughly.
 *
 * Usage: call NextHammingWeight((unsigned int) <number>)
 * 
 * Licence: Public domain.
 */

int HammingWeight (unsigned int number) {
	int i;
	int c = 0;
	for (i=0; i<sizeof(int)*8; i++) {
		if ((number >> i) & 0x1) {
			c++;
		}
	}
	return c;
}

unsigned int NewNumber (int ones) {
	unsigned int result = 0x1;
	result = result << ones;
	result--;
	return result;
}

unsigned int NextHammingWeight (unsigned int current) {
	unsigned int next = current;
	int i;
	for (i=0; i<sizeof(int)*8-1; i++) {
		if (((next>>i)&0x3) == 0x1) {
			// If the two bits being looked at are '01', switch them
			next = next ^ (0x3 << i);

			// We then have to 'reset' all of the bits before the switch.
			int ones = HammingWeight(next % (0x2 << i));
			next &= ~((0x2 << i) - 1); // zero those bits
			next |= NewNumber(ones); // 'reset' the bits
			break;
		}
	}
	return next;
}