用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;0 P/ B5 N; }' { y2 f0 i
lenUserMsg equ $-userMsg ;; t4 l; |9 ?- |9 h8 l) @
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '% O" C: Z4 d5 E' p! t, B
lenDisp2Msg equ $-disp2Msg ! Y/ n* _1 W( W" r' C
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a8 M: l8 j3 s) D. h x O( @* G
lenErrMsg equ $-errMsg $ K t. H3 h7 p4 p, i. O) \* L/ z
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section .bss ;8 f2 r5 e8 i8 A, q* D1 I
num resb 1' U+ e; ^3 \2 \6 k0 x
result resd 1
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buffer resb LEN_OF_OUTPUT+1 _8 O/ a/ V3 R }" ~
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section .text ;
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global _start
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_start: ; S: t$ U: Z/ F9 `, h# B
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg! f. g% D8 R3 X i) A; ~" g2 |
mov edx, lenUserMsg- P+ d$ @6 R3 c# j) S9 L
int 80h
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; read user's input
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mov eax, 3
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mov ebx, 0" \% r0 N ^9 C# Z" r/ J9 F
mov ecx, num
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mov edx, 1 ; length of input buffer9 n' E% n- Q9 _0 I K
int 80h9 f4 f: @3 m# G E3 D/ ]4 D+ f
; E. v# o$ e. i
mov eax, [num]' v& \" w! j' E8 z [5 P
and eax, 0xFF9 q: m' I- r4 v, t' n4 [! N! {
sub eax, 0x306 O# W+ q I7 K
jl ERROR, l7 }8 e( j& ^( r
cmp eax, 10" [# R. W' n+ Z4 {3 B( T( t
jl DO_CALC7 p5 Q# m8 C0 B! i: D A
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mov eax, 4
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mov ebx, 1
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mov ecx, errMsg; [: y4 m/ ~, s% H4 P& M& p0 _
mov edx, lenErrMsg1 y' K K8 {5 U. A
int 80h 1 z E/ m U/ n8 |3 K" `
jmp EXIT
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DO_CALC:+ I/ W+ M) a5 F) _
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.( a$ O4 z6 S6 ^3 w% h* S
mov [result], eax ; Save the result
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; print result+ d- e/ N* h: Y: Y3 V7 n1 ~
mov eax, 4
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mov ebx, 13 R$ u0 Q' T- h4 \; Y, t* ]9 o
mov ecx, disp1Msg1 H! W s* ~& D8 ~6 i
mov edx, lenDisp1Msg$ ^# T9 l2 q- q+ c4 |
int 80h
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mov eax, 4
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mov ebx, 1
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mov ecx, num6 u. ]* N3 x4 Y2 W& i7 O- D: M2 D
mov edx, 1
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int 80h 9 b* H7 i% s& }# G2 ~& M' K
mov eax, 46 b; { {. o/ U% t# ]1 f
mov ebx, 1& m8 ^9 r' U4 j0 A% f5 F8 {
mov ecx, disp2Msg
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mov edx, lenDisp2Msg" B9 F+ X( _9 r. x g4 e& B
int 80h
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; output number; c. K- ~4 P' J( L+ j, y
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY2 s7 |" v# R8 y: X4 N
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:7 q! V, U7 M; T0 N4 _& {
mov edx,0 ; clear dx prior to dividing edx:eax by bx
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div ebx ;DIV EAX/104 t2 B: k# r6 w; C7 J) t
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 5 ]4 M* P- v! U ]( q
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII: |* J S5 o2 K
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:) }0 s& ^+ z; s
mov eax, 4
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mov ebx, 11 ]9 j( U1 \; k6 L2 ]
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
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; Exit code# D. o2 S$ H; k, D1 m7 }3 L
EXIT:
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mov eax, 1
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mov ebx, 07 v. ]' x; [5 h# b5 n E
int 80h% }3 y" C, C2 {5 b" Y8 Y# u; a
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; Factorial function using recursion1 y) p$ v9 }0 h* K( H6 b
factorial:! B }9 e' \ C* P% \& U0 E- Z) m
; Check if eax is 0 (base condition)
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cmp eax, 0. M% T/ N3 b O( s; s
jz end_recursion
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; Save the current value of eax3 q8 Q2 f- } l
push eax! u* r3 F8 Z- n, {7 e
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; Decrement eax and call factorial function recursively, w( a+ J: V% d
dec eax( n* q9 c3 c6 J6 F
call factorial
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; Multiply the result returned in eax with the saved value of eax' Y7 R* ^6 @( f2 @/ h7 v4 S
pop ebx
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imul eax, ebx/ T( v- [7 j: c/ }
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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
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ret

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