用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 109 a& L2 O! h% d& V( y! K
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;1 K: b7 h2 e1 f* U5 u2 F6 f
lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '/ A! y1 w- m' t. j, ~( Z
lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '4 ~% `5 L( i4 U0 c$ s
lenDisp2Msg equ $-disp2Msg + e6 j3 N; E; k% i; O
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg , a0 L) B3 Q: C- R# b% ^8 v7 `
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section .bss ;% t% [7 _5 s4 R9 ^; C
num resb 12 _4 b) }- `( B, K# J, q; t8 l
result resd 1
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buffer resb LEN_OF_OUTPUT+1; Q) m7 Y! j4 M: L) U- C5 R4 f
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section .text ;
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global _start
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_start: ;
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mov eax, 4( A9 e1 ~5 F+ N
mov ebx, 1
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mov ecx, userMsg
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mov edx, lenUserMsg
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int 80h
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; read user's input
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mov eax, 3
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mov ebx, 0
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mov ecx, num 4 Q8 b P& }& Y3 T9 f9 ~
mov edx, 1 ; length of input buffer0 i% @$ E) o2 t4 O5 W0 P: G+ C/ r
int 80h
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mov eax, [num]
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and eax, 0xFF
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sub eax, 0x305 @$ J" E& B4 ?5 a7 o& `( K) u
jl ERROR4 \, R$ m# _# H0 M. w0 o @
cmp eax, 10, A/ e8 f2 Q6 [9 D
jl DO_CALC- [/ T! B4 S$ Y& z
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mov eax, 4
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mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h
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jmp EXIT
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DO_CALC:! f) f. M% u! @# W x, e, S, ], S4 O
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.+ Q; I7 Z3 K6 q" _' H4 f
mov [result], eax ; Save the result
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; print result) p. V, t" y5 n) O4 h2 ^# a3 o
mov eax, 4
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mov ebx, 18 K; B, q# I5 q5 ~& {$ i: f$ j2 }8 K
mov ecx, disp1Msg
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mov edx, lenDisp1Msg
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int 80h
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mov eax, 4# C- Z* o* W7 _( v; M# Z) A# I
mov ebx, 1
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mov ecx, num
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mov edx, 1
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int 80h ) u3 M& Z) u- b* I( S/ n
mov eax, 4: p7 W6 w( C3 [0 Y r# T- h
mov ebx, 1
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mov ecx, disp2Msg
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mov edx, lenDisp2Msg
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int 80h
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; output number
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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 " L# N; ?& q0 Z% O+ T' J7 w
ASC_LOOP:$ L+ V! x: N3 u4 D. Q5 Y! ^& Q D0 T
mov edx,0 ; clear dx prior to dividing edx:eax by bx7 J7 p% A0 P Z* s% G
div ebx ;DIV EAX/10+ O( X& p) P# c# S1 B
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+ {4 Q- s8 N( b! W" A; v2 s
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 REPEAT7 [. A: O4 Z* Q
END_ASC:
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mov eax, 4
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mov ebx, 1
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mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx& o+ n/ T/ b* M5 i0 g/ V
int 80h 6 Y) F3 }, t/ n2 v
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; Exit code
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EXIT:
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mov eax, 1
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mov ebx, 0
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int 80h7 |* }8 `: K- g3 }- |# `: l
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; Factorial function using recursion, y2 b- ^6 H8 O
factorial:
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; Check if eax is 0 (base condition)
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cmp eax, 0
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jz end_recursion
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; Save the current value of eax
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push eax# T1 e) @0 S, ~' A
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; Decrement eax and call factorial function recursively; t' ^5 @' q& X
dec eax9 D3 E; r& |0 ?
call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx7 y, E# t: x6 x% k
imul eax, ebx
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ret* Q* U$ ^& z% m9 {) L z3 f9 F: K
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end_recursion:0 Y" x5 g: C1 C0 q
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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