wowFact.asm

gistfile1.asm

fact:               ; fact 3 r0=3
  SUB sp,sp,#8      ;Adjust stack for 2 times
  STR lr,[sp,#4]    ;Save return address
  STR r0,[sp,#0]    ;Save argument n
  CMP r0,#1         ;compare n to 1           ; r0=3 ~~~ 1
  ;BGE L1
  SUB r0,r0,#1     ;else decrement n
  
  BL  fact          ;Recursive caller         ; r0=2
  SUB sp,sp,#8      ;Adjust stack for 2 times
  STR lr,[sp,#4]    ;Save return address
  STR r0,[sp,#0]    ;Save argument n
  CMP r0,#1         ;compare n to 1           ; r0=2 ~~~ 1
  ;BGE L1

  SUB r0,r0,#1     ;else decrement n          ; r0=1
  BL  fact          ;Recursive call
  SUB sp,sp,#8      ;Adjust stack for 2 times
  STR lr,[sp,#4]    ;Save return address
  STR r0,[sp,#0]    ;Save argument n
  CMP r0,#1         ;compare n to 1           ; r0=1 ~~~ 1
  MOV r0,#1         ;if so,return is 1
  ADD sp,sp,#8      ;Pop 2 items form stack
  MOV pc,lr         ;Return to caller