用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 103 d8 N; ?0 f% k' W% b0 ^
section .data ;
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userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;, g( Q: z$ `4 @$ Z1 u/ K
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg 2 f. m& }3 e4 B3 i* F% b4 C
disp2Msg db ' is '0 o- N! ]6 c1 C( I2 ]# b
lenDisp2Msg equ $-disp2Msg / _: _- P! s/ q! O, M! N
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg . \! E! `1 K) B/ U' O
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section .bss ;
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num resb 1; s9 M. K0 W$ @( C6 Z/ s
result resd 18 n/ Y+ o4 j2 W7 y c
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start( Z" W/ P0 a7 n5 s4 S
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_start: ;
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mov eax, 4
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mov ebx, 1% F" S$ ~" O' _& ^
mov ecx, userMsg* s# F4 n0 v, J/ U4 N8 L6 }
mov edx, lenUserMsg2 U. i$ n- [1 N _, I. C, q7 ]
int 80h& T q+ c& l% W: f, \! ]' B
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; read user's input3 U6 n5 J- ]" x1 B# i8 s
mov eax, 35 a4 ]* p2 x& [5 O- D
mov ebx, 0
mov ecx, num
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mov edx, 1 ; length of input buffer$ P6 t! ?# @( U) ~$ o/ I( }: I
int 80h+ Z& G3 {/ M J* f! j
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mov eax, [num]
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and eax, 0xFF
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sub eax, 0x30* ?0 q0 _: w+ V, K! z! ]
jl ERROR% L+ r1 K( M0 W3 l4 \( s
cmp eax, 10: }7 X4 |8 ], a; x; [- ^6 K% |
jl DO_CALC
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ERROR:
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mov eax, 43 D( }' v5 w8 I9 ]% o+ {) z( V4 X
mov ebx, 1
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mov ecx, errMsg y; G; H" a2 C, O
mov edx, lenErrMsg
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int 80h
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jmp EXIT; ?/ Q) I4 q- m2 n7 e& N$ I$ |1 a
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DO_CALC:
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call factorial! S" ]: W% b4 m9 S, B. a
; The parameter is in eax. After calling, the result will be stored in eax.
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mov [result], eax ; Save the result" \$ \7 e$ M! L
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; print result! `! H5 ^3 _ Z, p/ }1 j* {
mov eax, 4! t( c$ h: a F, C
mov ebx, 1& S5 v4 z5 G* A( q9 c! d
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; y$ ~2 |9 A- C* M/ E5 M2 q
mov ecx, num
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mov edx, 1; R2 F0 P6 S" X8 @% O- B
int 80h
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mov eax, 4- [ G) J6 u0 W% Z) W
mov ebx, 19 L: n7 c+ ?! a0 n# @
mov ecx, disp2Msg
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mov edx, lenDisp2Msg( [8 h. e. j' O( V8 l; \# L
int 80h
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY7 c8 ]! R0 G& X/ ? t. V+ p8 d
mov byte [buffer+LEN_OF_OUTPUT],0x0a' e+ u- _5 W k* m2 G. G* q8 p( L
lea esi,[buffer+LEN_OF_OUTPUT]4 Z1 A7 I; X( {+ D9 ~
mov ebx,10 3 [2 n. l) U, ~
ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx
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div ebx ;DIV EAX/10" Y9 i5 f) [; P# e
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
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dec esi ; store characters in reverse order
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mov [esi],dl
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cmp eax,0 ' m. p# j) _* q" s, _7 r6 b9 U
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII) G7 r5 N# R1 L
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:1 ?0 p3 R7 L' }
mov eax, 4) G* E$ v' n: V' n' u4 y9 k
mov ebx, 1
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mov ecx, esi- M* {2 _) e% u$ i7 y7 G4 W& t$ E
lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx+ z5 ]% @$ C/ [7 a
int 80h
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; Exit code& b( h# j G7 a# c* o* t8 i0 `
EXIT:" x6 ]% [7 v5 ]; u( Y Y3 W6 ]9 B
mov eax, 17 x- [4 l- v3 h0 H8 o7 U
mov ebx, 0
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int 80h" y/ A9 R- s# b$ w1 b& `$ z0 a
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; Factorial function using recursion
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factorial:5 [7 w% v) W4 R* q" X; w1 x* L, l2 n
; Check if eax is 0 (base condition)7 B. t3 k$ j. A& K3 Y
cmp eax, 00 q1 _- p6 J- |8 O9 y# ]
jz end_recursion
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; Save the current value of eax
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push eax! `: e2 y, A3 p
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; Decrement eax and call factorial function recursively
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dec eax
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call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx
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imul eax, ebx$ ^* d8 I' V7 E) K; F2 Q
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ret
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end_recursion:
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; Return 1 when eax is 0 (base condition)
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mov eax, 10 h( c H" c" ?
ret

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