md1

    .text
    .align  2
    .global asum
    .type   asum, %function
asum:
    movs r1, r0
cond:
    bcs error
    subs r1, r1, #1
    bls exit
loop:
    adds r0, r0, r1
    b cond
error:
    mov r0, #0
exit:
    bx lr
    .size   asum, .-asum