用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10; L& V) G# v- t- y' M5 q. j2 f% |
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;' |5 F9 ` O6 L% K) \2 [4 B
disp1Msg db 'The factorial of '* j* u0 s7 |7 p+ A5 E/ K
lenDisp1Msg equ $-disp1Msg ) ^+ O$ W+ T3 y3 _
disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg ( G3 |5 d! b$ s8 {& R6 X
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg
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section .bss ;6 }4 \3 F! l/ `0 ]
num resb 10 W: ^1 F) _% N5 _( e! u! j6 _
result resd 1
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buffer resb LEN_OF_OUTPUT+1/ w6 x/ y- d' ]
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section .text ;( w1 ]" e9 L$ G% }4 Z/ k K
global _start' J. Z% e2 c+ F& r
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_start: ;
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mov eax, 4
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mov ebx, 1
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mov ecx, userMsg* n5 c8 w9 V- z
mov edx, lenUserMsg
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int 80h8 a9 O: d3 A9 X+ l: A' e, b
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; read user's input% n% @2 j) _- \3 H, X- U& F: J
mov eax, 3
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mov ebx, 0
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mov ecx, num , [$ N. V# a1 Y$ k( F4 x
mov edx, 1 ; length of input buffer5 |) V/ h8 i" i
int 80h& d, G9 z I9 [" r
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mov eax, [num]! f4 f4 \9 G( ]. ~$ F- H8 l& A# G% @
and eax, 0xFF
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sub eax, 0x30" L$ Y+ O& o# A, D; l$ F0 H9 h2 d
jl ERROR
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cmp eax, 10
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jl DO_CALC
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ERROR:
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mov eax, 4
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mov ebx, 1+ t% J& c8 ~+ p" G9 ?. W) a
mov ecx, errMsg+ D: o" f% |( O
mov edx, lenErrMsg4 P A6 R7 v0 t0 _# T
int 80h
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jmp EXIT
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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.
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mov [result], eax ; Save the result
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; print result: B; ~2 U# n" I e# L5 K! P( [' B
mov eax, 4
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mov ebx, 1/ S4 |: o8 G; L& Z1 n# }
mov ecx, disp1Msg4 n! Q3 p+ b% @ {3 Q2 l5 U
mov edx, lenDisp1Msg C( v5 X% W2 k; _# j& m( {( a
int 80h : x3 z1 Q" S' Z+ m
mov eax, 4 v- _! e: N( b0 Z; m
mov ebx, 1
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mov ecx, num: K3 J6 x& s0 }: F& S- J# Q
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, disp2Msg1 X+ b9 s8 c* U$ d
mov edx, lenDisp2Msg
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int 80h
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; output number& j& b! B" i7 P) [5 Z" y7 a
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:2 G9 W- C( ]: I% d5 v# w( L
mov edx,0 ; clear dx prior to dividing edx:eax by bx" I4 _4 m: b6 z5 p- z
div ebx ;DIV EAX/10. I0 R c* M1 {5 y8 X. g
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER " b* ]7 L. [ _$ w; d% G1 S
dec esi ; store characters in reverse order
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mov [esi],dl
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cmp eax,0 ) V% T& a9 ~ o* H, X, U k, l
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII8 d% a: W$ L% \. L
jmp ASC_LOOP ;ELSE REPEAT. ]( x& I0 C" Q) Y2 x( W
END_ASC:' j+ F. {* l1 X+ E& ?' h
mov eax, 4+ G; o5 w: R3 @: Z! Z
mov ebx, 1, Y& M. ?6 d* z. M% q Q1 c9 X4 ~
mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx
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int 80h 4 o0 }# n J' h, T1 r
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; Exit code
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EXIT:5 R3 D6 k6 b5 b, U6 i4 z
mov eax, 10 {5 e6 x" V/ x7 \6 n B0 G) P3 n
mov ebx, 0# |* ]" v* _0 A- k/ \" V
int 80h
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; Factorial function using recursion
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factorial:. j2 H" l& D7 G& }: ~
; Check if eax is 0 (base condition)
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cmp eax, 0& i# n' S' t! f& h- Z; _
jz end_recursion3 u+ n6 M6 z# ]' r
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; Save the current value of eax
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push eax9 y+ b9 `, k/ M6 Y# ~6 q7 n
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; Decrement eax and call factorial function recursively8 @1 F) t" s& n( o4 t% W
dec eax X3 G9 m/ H* Y3 X
call factorial$ i; [+ D4 N% c6 }: C3 @6 O8 D
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; Multiply the result returned in eax with the saved value of eax
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pop ebx. h+ ^+ t4 `' W A8 U4 o n' O1 L
imul eax, ebx/ P( V5 K2 z! z4 h2 r1 X
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ret u. o6 @1 v: ~6 ^- D6 j/ `
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end_recursion:( J+ \" Z. P8 A A0 y [% u- u
; Return 1 when eax is 0 (base condition)- W7 j, t0 {8 G. T
mov eax, 1
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ret

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