.cpu cortex-m4
	.thumb
	.syntax unified
	.globl multiply
	.text
	.thumb_func
	// R0 = a, R1 = b, R2 = result (m), R3 = odd/even mask/result
multiply:
	MOVS.N	R2, #0		// set result to 0
	CMP.N	R1, #0
	BEQ.N	exit		// goto exit if b == 0
multiply2:
	CMP.N	R1, #1
	BNE.N	check_even	// goto check_even if b == 1
	ADDS.N	R2, R0		// move a to result
	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