用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;$ X, B& o# T' ^9 I! ] w3 d9 {
lenUserMsg equ $-userMsg ;; W5 o1 d$ X: C' u7 t6 V
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg
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errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg
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section .bss ;
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num resb 1% h1 D' a% J$ u/ I) B F- K6 P
result resd 1
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buffer resb LEN_OF_OUTPUT+1
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section .text ;5 p N! i' y: E4 S( G! l9 u$ |
global _start
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_start: ;
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mov eax, 4/ h9 _) `- Z6 `0 g* f7 m
mov ebx, 1
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mov ecx, userMsg0 x4 q& H0 J% x' a% D$ o7 n
mov edx, lenUserMsg$ U, a7 [. q3 o$ e
int 80h' X: @- g% c7 \: u; Y
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; read user's input3 v$ R9 Y- F! d) R
mov eax, 3' K. t7 p K5 A# O. x: `" @
mov ebx, 0
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mov ecx, num - O/ g) E* H' u. J* b3 n
mov edx, 1 ; length of input buffer0 |* f, M' C a k. ]
int 80h8 [' ?1 s5 [* l, d$ A V( ?' O
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mov eax, [num]# Y+ I) m: u9 q! w
and eax, 0xFF- ], g, c0 l9 H4 c7 G
sub eax, 0x30- ~3 g& c, z$ A
jl ERROR/ W+ A# X8 ]8 g. W; d: ^& o' T
cmp eax, 10; \# a. |* Y; M4 S
jl DO_CALC
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ERROR:
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mov eax, 4" l* `1 j3 \ y+ s$ z
mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h 2 P4 i/ W* q, t. ]/ d# y
jmp EXIT& g1 _( ?5 k* {, y7 p& g' B( y6 U9 l
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DO_CALC:0 @( M$ X" F7 E% |4 W( q) C
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.$ m$ ?5 s8 a# y
mov [result], eax ; Save the result
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; print result
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mov eax, 44 P6 f' J1 G# s- b
mov ebx, 1/ o$ o4 q; D5 O. p; F$ H
mov ecx, disp1Msg
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mov edx, lenDisp1Msg
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int 80h
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mov eax, 4
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mov ebx, 1
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mov ecx, num
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mov edx, 1
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int 80h
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mov eax, 4
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mov ebx, 1
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mov ecx, disp2Msg
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mov edx, lenDisp2Msg
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int 80h 9 E% X3 T" O: W1 { A
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; output number4 l; E+ Z! ~/ |8 J% v
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
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mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10
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ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx2 V4 U7 J3 ]0 J3 W; N& }7 x
div ebx ;DIV EAX/10% M$ p' f/ ]) y; |0 Y
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER & ~( x8 |9 Z: z! X
dec esi ; store characters in reverse order2 u: Q% B5 \" ~) Q7 j @
mov [esi],dl
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cmp eax,0
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jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:" d2 O8 H) g3 l9 F8 |& N
mov eax, 4; ^/ b7 n7 ^3 p j+ O ^& u
mov ebx, 1! G/ q0 V1 E$ k0 Y' j4 [; C k. ] J% E
mov ecx, esi0 h' b/ m# x T+ ~" o. M5 J
lea edx,[buffer+LEN_OF_OUTPUT+1]% H2 @& T: R8 K5 E( y9 O6 j
sub edx, ecx
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int 80h
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; Exit code
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EXIT:- ^5 n* Q, u; l& V9 i! D1 a- R) P
mov eax, 18 x6 s+ Y( n9 c5 _3 Y/ }7 T" {
mov ebx, 0$ l: w- f6 Q4 B6 T6 q
int 80h
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; Factorial function using recursion' [7 B, l) q% _; f
factorial:
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; Check if eax is 0 (base condition)9 @+ h' }+ K' P9 l u; G, N
cmp eax, 0- A$ C1 b7 S! E. I! S
jz end_recursion
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; Save the current value of eax7 d* U7 Z7 y. Y0 U. `, ], {
push eax* X. m& u t: x e [
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; Decrement eax and call factorial function recursively
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dec eax4 f$ V1 i1 G# H8 M7 G; W
call factorial
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; Multiply the result returned in eax with the saved value of eax% z5 H4 S0 [7 H+ I4 Y* u' y0 d' D8 h
pop ebx
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imul eax, ebx1 U6 I7 Q" {1 }+ L# S
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ret
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end_recursion:5 V# h* k' Y* a! `) W* P
; Return 1 when eax is 0 (base condition)* ~/ y6 u! Q" n/ l9 D, D4 U
mov eax, 1; {+ Q$ g% v2 t
ret

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