用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;( \8 G3 p% o* K! T
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;
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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 . _# M0 r" ]: @' p( v8 `. H
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a u4 X, }) ]; X7 Q/ M7 s# d
lenErrMsg equ $-errMsg , P6 T/ i% a; q$ h& P2 q
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section .bss ;4 d: s' c7 U( t! U! ~) z
num resb 1. Z+ j! v, A# ]0 N$ N$ S. A. S
result resd 1
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buffer resb LEN_OF_OUTPUT+1& Q1 V4 _, _! K) o
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section .text ;' _- c- Q" B3 h0 O& y1 @
global _start( P9 K8 V7 \/ W0 p
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_start: ;
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mov eax, 4
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mov ebx, 1, T- B1 Z% T- A$ g$ L8 x
mov ecx, userMsg' B# p! z8 y( h. s' b
mov edx, lenUserMsg( ^1 X+ D/ [8 A2 }- @; r' L
int 80h% A$ G: M; X$ T- K& I: ^ F
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; read user's input
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mov eax, 3
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mov ebx, 0/ H& ^# f" G: M/ q$ e& L4 Q
mov ecx, num % F( {1 H3 ?! ?" V& a P- P
mov edx, 1 ; length of input buffer
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int 80h7 l: R2 {# P% l( v$ w
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mov eax, [num]- s( j L# b% `5 j: \3 H0 p" P! X0 ]
and eax, 0xFF. Y4 }5 B# L' u* I2 u4 ^
sub eax, 0x30
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jl ERROR: S7 R0 n0 w6 k1 |) b
cmp eax, 10
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jl DO_CALC
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ERROR:
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mov eax, 41 y2 y# q: Q' X+ ]9 y
mov ebx, 13 ^" o" V/ N8 M1 Y
mov ecx, errMsg2 o7 x! C2 h5 z! {/ Z
mov edx, lenErrMsg
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int 80h 9 k8 d% g8 L A8 c0 T2 x* G
jmp EXIT1 `4 _' x" c2 Z/ i
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DO_CALC:
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call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.# a" I- v& p5 ?
mov [result], eax ; Save the result. F; w' U! n5 i8 H' G7 E
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; print result
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mov eax, 4' }; w8 v( Z9 l3 _7 Q8 M
mov ebx, 1
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mov ecx, disp1Msg9 U2 D2 r' d( C1 a5 m
mov edx, lenDisp1Msg
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int 80h
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mov eax, 4; y- X, a" W/ u
mov ebx, 14 w& O2 i5 }) c% J' E+ }
mov ecx, num5 E( }7 ?+ U7 B% k5 k! o( M
mov edx, 1
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int 80h # U; Q+ ~! I4 X3 T( M% I) u
mov eax, 4" |& Z/ E' q2 _! ^+ o# ]
mov ebx, 1
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mov ecx, disp2Msg4 _6 m8 F/ K9 \* c. l, R9 i
mov edx, lenDisp2Msg2 N& M5 M8 i. k/ |% y
int 80h
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY% o s8 [* Y9 [7 L9 v
mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]: P, P* I; Y8 s' H. C! H4 M
mov ebx,10
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ASC_LOOP:: W( ?. i. S2 z5 w2 p
mov edx,0 ; clear dx prior to dividing edx:eax by bx0 b" f; a# W& w6 A) b e9 t- l9 z
div ebx ;DIV EAX/10& v% Q( q- M! }1 F
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
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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:
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mov eax, 4
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mov ebx, 1
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mov ecx, esi$ H0 k; w4 x6 ?) ^4 @
lea edx,[buffer+LEN_OF_OUTPUT+1]$ O5 O3 N/ V* @
sub edx, ecx
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int 80h
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; Exit code
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EXIT:+ |6 w) b1 }1 {8 U) ~2 o8 _0 n
mov eax, 1
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mov ebx, 0
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int 80h
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; Factorial function using recursion# [" {; I1 m& }: M7 y4 v0 P1 P
factorial:" e8 Q, \1 s3 O3 c; D' l
; Check if eax is 0 (base condition)4 L: \( V3 m4 `, r0 Q/ M
cmp eax, 0) Z: P; p" j& ]( T s
jz end_recursion" O% q, l$ Y# m3 }. @
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; Save the current value of eax
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push eax
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; Decrement eax and call factorial function recursively' z) {; E/ p( l) K, U" C
dec eax
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call factorial
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; Multiply the result returned in eax with the saved value of eax X( A$ m( G6 P6 E: ~% I
pop ebx, o8 U0 q! x/ ^, Q" _/ f" v$ \
imul eax, ebx* N' G0 c1 h/ S
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ret
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end_recursion:0 H& t; p& M4 F f7 \3 X
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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