W1.2: assignment 5: first try, not working

assignment_assembly/assignment3/multiply.asm

@@ -4,15 +4,30 @@
 	.globl multiply
 	.text
 	.thumb_func
+	// R0 = a, R1 = b, R2 = result (m)
 multiply:
 	MOVS.N	R2, #0		// set result to 0
+multiply2:
 	CMP.N	R1, #0
 	BEQ.N	exit		// goto exit if b == 0
-loop:
+
-	ADDS.N	R2, R0, R2	// add a to result
+	CMP.N	R1, #1
-	SUBS.N	R1, #1		// substract 1 from b
+	BNE.N	check_even	// goto check_even if b == 1
-	BEQ.N	exit		// goto exit if b == 0
+	MOVS.N	R2, R0		// move a to result
-	B.N		loop		// loop otherwise
+	B.N	exit		 	// goto exit
+check_even:
+	MOVS.N	R3, #1		// set R3 to 1 as bit mask
+	ANDS.N	R3, R1		// and R3 (bit mask) with b
+	BNE.N	odd			// goto exit if b == 0
+even:
+	LSLS.N	R0, R0, #1	// a = a << 1
+	LSRS.N	R1, R1, #1	// b = b << 1
+	B.N 	multiply2	// recurse
+odd:
+	ADDS.N	R2, R0		// add a to result
+	LSLS.N	R0, R0, #1	// a = a << 1
+	LSRS.N	R1, R1, #1	// b = b << 1
+	B.N 	multiply2	// recurse
 exit:
 	MOVS.N	R0, R2		// move result to R0
 	BX.N	LR