fact:
  ld [fp+12] -> %r0      / This is the base case.
  cmp %r0, %g0           / If i == 0, return val_so_far
  bne l1
  ld [fp+16] -> %r0
  ret

l1:
  ld [fp+16] -> %r0      / Replace val_so_far
  ld [fp+12] -> %r1      / with (val_so_far * i)
  mul %r0, %r1 -> %r0
  st %r0 -> [fp+16]

  ld [fp+12] -> %r0      / Replace i with i-1
  add %r0, %gm1 -> %r0
  st %r0 -> [fp+12]

  b fact                 / Branch back instead of doing recursion.

main:
  push #4
  st %g1 -> [sp]--
  mov #5 -> %r0
  st %r0 -> [sp]--
  jsr fact
  pop #8
  st %r0 -> [fp]
  ret