factorial in ARM assembly

factorial.s

;R0 parameter
factorial
	PUSH {R1, R2, LR}
	CMP R0, #1
	BEQ ret ; return 1
	MOV R1, R0 ; kopiera R0 till R1
	SUB R0, R0, #1 ; dec R0
	BL factorial ; anropa factorial
	MUL R2, R1, R0 ; int result = fact(n-1)*n
	MOV R0, R2 ; R0 = result
	POP {R1, R2, LR} ; return
ret
	MOV R0, #1 ;return 1
	POP {R1, R2, LR} ; return

lärarenskod.s

fact ; Assume R0 contains the input value,
 ; and R0 is also containing the return value
          PUSH {R1,LR}
         MOV R1,R0 ; R1 = n
         CMP R0,#1 ; if n>1 recursively call
         BGT fact_next
         MOV R0,#1 ; if n<=1 the return 1
         B fact_return
fact_next
         SUB R0,R0,#1 ;
         BL fact ; call fact(n-1)
         MUL R0,R0,R1 ; return fact(n-1) * n
fact_return
         POP {R1,PC}

thomas.s

main
	MOV R1, #5
	MOV R2, #1
	BL REK
STOP B STOP
REK
	CMP R1, #0
	IT EQ
	BXEQ LR
	MUL R2, R2, R1
	SUB R1, R1, #1
	BL REK