AREA    |.text|, CODE, READONLY

;   int factorial(int N);

    EXPORT  factorial

factorial               ; On entry, N is stored in R0.
    MOVS    r1, r0      ; R1 is our loop counter. Copy N to R1 and test.
    MOVEQ   r0, #1      ; if (R1 == 0) Set result to 1 and fall through to return...
loop
    SUBNES  r1, r1, #1  ; if (R1 != 0) Decrement R1 and test.
    MULNE   r0, r1, r0  ; if (R1 != 0) Result = R1 * Result.
    BNE     loop        ; if (R1 != 0) Loop.
    MOV     pc, r14     ; Return with result in R0.

    END