用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10* F0 t% w+ l; t& s. z$ w+ [ }. [
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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 ;
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disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '9 ^# s) W6 R( U/ |' E( B
lenDisp2Msg equ $-disp2Msg
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errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a9 H6 K5 E3 ^/ C0 y% s
lenErrMsg equ $-errMsg ' k2 L+ C- s5 g: o( G% F
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section .bss ;5 a. ~+ Y% \7 _8 y; \* G" D, Q2 R
num resb 1
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result resd 1) O9 D7 w: s8 X+ P! T% J
buffer resb LEN_OF_OUTPUT+1. |$ k5 r r0 L$ g
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section .text ;- V6 `8 u. s; h2 ]6 }
global _start/ I; H& X* i/ X3 y7 f, a3 C
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_start: ;" I0 a" C$ {% D
mov eax, 4
; _6 v, W1 C2 Y. }0 Y, A- Q+ E
mov ebx, 1) y$ j- d) m2 c8 S
mov ecx, userMsg: l" x) K& V+ f2 [
mov edx, lenUserMsg8 m8 B4 Y+ h8 B' M2 E6 v
int 80h3 w* ^4 \! @% E" t5 m, b
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; read user's input
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mov eax, 3
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mov ebx, 0/ S. j: d, Q, X: K. M# n
mov ecx, num 7 C' |0 ]6 H1 G6 ]
mov edx, 1 ; length of input buffer8 L2 A" L" O0 l, z
int 80h/ _: I+ i- t' T
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mov eax, [num]
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and eax, 0xFF* A0 b+ m0 @3 X
sub eax, 0x301 t3 Q& w3 p% w% ~6 i: ?9 z
jl ERROR, T' k. v" b/ H3 m
cmp eax, 100 q( O9 ~4 ~1 J) t# b
jl DO_CALC
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ERROR:/ }! ^5 u1 X' C1 P7 m! u
mov eax, 4; {" g+ m5 x. Q/ U" [8 Z" D
mov ebx, 1+ B) O, [$ k2 P# O
mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h : V8 u. A5 n; c3 j1 S# C
jmp EXIT0 ]1 \' |. D+ o C! b* g
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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.: b- b4 f& K) i, M- ~3 v2 E1 i
mov [result], eax ; Save the result
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; print result$ [6 w/ c) {; D2 }
mov eax, 42 Q$ g2 r5 j- G' L% c0 M
mov ebx, 1- N$ D( ]0 q9 K9 g! l5 W0 w: I
mov ecx, disp1Msg
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mov edx, lenDisp1Msg7 ~. n4 T, x$ j8 W
int 80h
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mov eax, 40 G+ R% g# Y# h7 q# W/ z( _; X1 m! h
mov ebx, 1
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mov ecx, num7 E8 z' Q! z5 x
mov edx, 1
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int 80h
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mov eax, 4
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mov ebx, 19 j$ n8 t# o4 P
mov ecx, disp2Msg* N/ B y+ z; x8 ^1 _" Y; j
mov edx, lenDisp2Msg, g; M7 w, c- `7 d' [3 u m
int 80h 5 v1 |% u5 A, @2 k
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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]. r+ ]4 q! j* S; ^& X7 D5 m6 G
mov ebx,10
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ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx
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div ebx ;DIV EAX/10+ r$ E/ o& B' _0 Q6 E E( m+ a
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
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dec esi ; store characters in reverse order, X7 C) K3 k7 \# S% Z
mov [esi],dl# ]5 |) o6 Y6 H9 n# J
cmp eax,0
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jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII7 Z8 b" X3 k" }2 @1 s- N9 l* W
jmp ASC_LOOP ;ELSE REPEAT8 V- I2 f \# d! x1 ?
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mov eax, 4
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mov ebx, 1% T; j3 i( v! {4 n; e2 T
mov ecx, esi7 Y0 v7 I! l8 h8 W8 }0 _4 t
lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx
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int 80h ! C* Q* z5 X. y1 F2 ]8 I* `
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; Exit code6 p+ u7 l- }6 N" W% f2 w3 m x
EXIT:, Q; Y" \- P" R, w% U5 d
mov eax, 1* D5 C: [, ?# o" t1 ^
mov ebx, 00 \) h7 k# I7 W3 ~. B
int 80h
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; Factorial function using recursion* D) H" a! m7 S& C- }6 l0 c/ k% Y- Q
factorial: T, A( V4 t1 x V! t+ T8 ^* X
; Check if eax is 0 (base condition)
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cmp eax, 0, U X3 X; a' x4 C, ^
jz end_recursion
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; Save the current value of eax( M1 d5 x6 V( ~- i, _0 U
push eax
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; Decrement eax and call factorial function recursively
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dec eax0 t0 \" h- @) z* ], }' x0 Z1 s8 `
call factorial( L2 Y/ H8 L1 r4 V2 p- S
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; Multiply the result returned in eax with the saved value of eax
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pop ebx7 F% h) o- P; I3 S- G/ o
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)0 e; K3 Q8 }0 g+ l' H5 j# y0 a0 o( w: F
mov eax, 1
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ret

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