.data
B0: .fill 0x55555555
B1: .fill 0x33333333
B2: .fill 0x0F0F0F0F
B3: .fill 0x001F001F
B4: .fill 0x0000003F

.text

;int countbits(int x) {
countbits:
	;x == r1

	;load address of B0 into r3
	ldil r3, B0@lo;
	ldih r3, B0@hi;

	;x = (x & B0) + ((x >>  1) & B0);
	;r0 = (x >> 1)
	lrs r0,r1,1;

	;load B0 into r2
	ldw r2, 0(r3);

	;(x >> 1) & B0	
	and r0, r0, r2;

	;x & B0
	and r1, r1, r2;

	;x = (x & B0) + ((x >>  1) & B0);
	add r0, r0, r1;

	;load B1 into r2, use displacment for address of B1 (or add?)
	ldw r2, B1-B0(r3);

	;x = (x & B1) + ((x >>  2) & B1);
	lrs r1, r0, 2;
	and r1, r1, r2;
	and r0, r0, r2;
	add r0, r0, r1;

	;x = (x + (x >>  4)) & B2;
	ldw r2, B2-B0(r3);

	lrs r1, r0, 4;
	and r1, r1, r2;
	and r0, r0, r2;
	add r0, r0, r1;

	;x = (x + (x >>  8)) /*& B3 */
	lrs r1, r0, 8;
	add r0, r0, r1;

	ldw r2, B4-B0(r3);
	;x = (x + (x >> 16)) & B4;
	lrs r1, r0, 16;
	add r0, r0, r1;
	and r0, r0, r2;

	;return x;
	ret;
;}