add basic bit operations

bit.asm

@@ -0,0 +1,82 @@
+mov r1, 0
+qcall clz
+add zr, zr, zr
+mov r1, 0x1
+qcall clz
+add zr, zr, zr
+add r1, zr, 0xAAAA
+lsl r1, r1, 6
+qcall popc
+
+pub rotate_left:
+	; (r1 >> r2) | (r1 << (32 - r2))
+	sub r3, zr, r2
+	add r3, r3, 32
+	lsr r3, r1, r3
+	lsl r1, r1, r2
+	or r1, r1, r3
+	
+	jmp r13
+
+pub rotate_right:
+	; (r1 << r2) | (r1 >> (32 - r2))
+	sub r3, zr, r2
+	add r3, r3, 32
+	lsl r3, r1, r3
+	lsr r1, r1, r2
+	or r1, r1, r3
+	
+	jmp r13
+	
+pub clz:
+	; special case 
+	mov r4, 0
+	; since we start the loop by shifting r2 load twice the value we need
+	mov r2, 32
+	mov r3, r1
+	; divide and conquer algorithm
+	clz_loop:
+		; next finer step
+		lsr r2, r2, 1
+		; abort if there is no finer step
+		cmp r2, 0
+		je clz_end
+		; see if there are still some 1 bits left with this additional shift
+		lsr r3, r3, r2
+		add r4, r4, r2
+		cmp r3, 0
+		jne clz_loop
+		; undo shift if it resulted in zero
+		sub r4, r4, r2
+		lsr r3, r1, r4
+		jmp clz_loop
+	clz_end:
+	; we calculated the position of the last 1 from the least significant side
+	; inverse is what we want (position of last 0 from most significant side)
+	mov r1, 31
+	sub r1, r1, r4
+	jmp r13
+	
+pub popc:
+	mov r2, 0x0101		; load mask of 0x01010101
+	lsl r2, r2, 16
+	or r2, r2, 0x0101
+	
+	mov r3, 8	; bits in byte 
+	mov r4, 0	; pop count of each byte
+	popc_loop:
+		and r5, r1, r2 ; extract least significant bit of byte
+		add r4, r4, r5
+		
+		lsr r1, r1, 1 ; cycle through bits
+		sub r3, r3, 1
+		cmp r3, 0
+		jg popc_loop
+		
+	; sum up bytes
+	lsr r2, r4, 8
+	add r4, r4, r2
+	lsr r2, r4, 16
+	add r4, r4, r2
+	and r1, r4, 0xFF ; mask out end result in lowest byte
+	jmp r13