用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;7 W) q4 u$ a2 V8 n# J
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '5 n- W i7 X4 w: f' A
lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg 7 J+ O" W* B. ?& j
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg
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section .bss ;
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num resb 1
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result resd 1% f* z; `) P9 Q& ]. A: J/ z7 H
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start+ y0 ]) ?1 V1 n2 j j f
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_start: ;
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mov eax, 4& `* p* I& T! q9 b
mov ebx, 1
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mov ecx, userMsg
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mov edx, lenUserMsg
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int 80h
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; read user's input
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mov eax, 3
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mov ebx, 05 |' K+ _1 I3 X* ^1 V
mov ecx, num
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mov edx, 1 ; length of input buffer
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int 80h
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mov eax, [num]
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and eax, 0xFF
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sub eax, 0x30
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jl ERROR
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cmp eax, 107 e I: a% F* r; Q% v+ K1 W
jl DO_CALC
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ERROR:
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mov eax, 4& n' v& P- t9 r6 d
mov ebx, 1; F$ `7 s2 H) Q; F) t- {
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:2 @% b2 [- U3 V T1 b! V6 y2 Z
call factorial. N6 M+ B' e8 i( }6 }4 v% F8 F1 `
; The parameter is in eax. After calling, the result will be stored in eax.
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mov [result], eax ; Save the result$ r% U, ]$ U3 ?' o
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; print result
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mov eax, 4
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mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg
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int 80h 0 m1 s$ S( F! }) b5 _ r( J
mov eax, 48 R) U0 L3 }8 d/ p
mov ebx, 1
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mov ecx, num) o4 z/ q1 C. L3 z4 S7 t% }
mov edx, 1 `, X5 i8 Q* _' w* c" Z! y g7 C' K
int 80h
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mov eax, 44 M3 O% _' J/ J# Y
mov ebx, 1
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mov ecx, disp2Msg
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mov edx, lenDisp2Msg0 B. {# |6 S, o. }" @
int 80h 4 O9 @# `" G* f9 i' Q9 B4 t
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; output number. ^; x8 `- k! U/ Z' B# t
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY% N4 m. `( O+ y. s3 Q
mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]* ^0 y: w6 ?$ O* E/ u, L9 c# J" q
mov ebx,10 + a9 i1 S# P+ {! v7 n9 i
ASC_LOOP:" i- M; f0 y. b" `3 N4 U
mov edx,0 ; clear dx prior to dividing edx:eax by bx2 ?& k0 d: r$ _" h+ A/ B1 h: I3 R
div ebx ;DIV EAX/10
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add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER 0 p2 _$ P% q4 |4 n1 }& Z& `
dec esi ; store characters in reverse order3 n; {& o" o4 Z5 O5 H0 I
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' Y+ t6 t3 t5 m! c& U
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:
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mov eax, 48 W; |8 v s4 n1 V
mov ebx, 1
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mov ecx, esi; x* y2 q7 A/ S- ~' [( c
lea edx,[buffer+LEN_OF_OUTPUT+1]1 h6 e7 a& x# P& j
sub edx, ecx
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int 80h
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; Exit code. v, @, ^8 P, v8 G4 Z! q( ]
EXIT:: [6 m1 O1 R2 n3 R% b$ b8 Y
mov eax, 1; e. h3 M2 y' R% [( Z
mov ebx, 0
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int 80h
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; Factorial function using recursion
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factorial:1 n8 _6 P- ?% S, \( \. s, s
; Check if eax is 0 (base condition)
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cmp eax, 0, o3 C$ Z% Y/ l. K
jz end_recursion
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; Save the current value of eax
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push eax" p) [! T# g4 P# x( B D Z; u& p6 n
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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% F3 A& a# F" I5 r
imul eax, ebx
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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, 1
ret

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