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: ' ;
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lenUserMsg equ $-userMsg ;: i# V( _' `" o3 o+ }% P( W* o
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg 1 {0 f& ~$ R. E+ q7 F& ]# b
disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg
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errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg
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section .bss ;
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num resb 15 o: v' M+ I4 C% v: S( U! V: w! z
result resd 1* {$ J9 y7 @& a$ T2 J3 Q
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start
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_start: ;. R0 ^, \* B8 k6 E8 e7 {, r }5 B
mov eax, 4
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mov ebx, 1# `+ \: L( n8 j8 z2 Y! A
mov ecx, userMsg
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mov edx, lenUserMsg& N# ^- f8 s% p( t, \4 w) U# |/ s
int 80h3 f: o; [: D, a: z2 }. Z
; [( Q' ?1 \6 G; O/ I& B3 U9 L. ]
; read user's input' p& k8 o5 |7 o* Q j# Z
mov eax, 3
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mov ebx, 0' g# V; v( I+ Z$ i* g- i
mov ecx, num ; Z+ D4 _1 F& ~! J: L" A7 T- _
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, 0xFF9 T2 l3 G% N; N- X8 B7 ^
sub eax, 0x30
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jl ERROR( @$ [) a0 x- R$ y2 q% u
cmp eax, 10. P$ H' A: a$ D* ?
jl DO_CALC3 }6 a6 } \+ F6 {& }7 i; J9 B6 H1 ?6 z
ERROR:
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mov eax, 4
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mov ebx, 1
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mov ecx, errMsg! _6 J# T" w3 e
mov edx, lenErrMsg! U* g# T7 |/ V, e6 f
int 80h 2 }5 Y) D9 p9 [ h
jmp EXIT
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DO_CALC:: F) \1 H; n m2 l1 v5 R1 S0 A
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- a/ b ?. f; X$ ^5 H, B0 S0 V
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; print result: y3 g0 p1 v$ \ W; m' G$ y
mov eax, 4
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mov ebx, 1
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mov ecx, disp1Msg; ^9 E+ G/ G l" [
mov edx, lenDisp1Msg
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int 80h , B n/ b6 R; K7 `! [# r
mov eax, 4
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mov ebx, 1- {4 C5 Y$ H4 Z% m g; [1 K
mov ecx, num
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mov edx, 17 X. `8 ^6 s% s8 T, n
int 80h / T( ` y( N/ e" r7 r" U
mov eax, 4
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mov ebx, 18 ]: s. i5 K. ]0 ]
mov ecx, disp2Msg' O! D4 Q* }! B. C8 `
mov edx, lenDisp2Msg
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int 80h
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; output number8 M5 C! q/ G; p) V% O% S' l+ T
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY6 Q* i; i% j" b1 W( R2 u
mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]( A3 ?0 [; H9 g5 E( u! I0 V5 w N
mov ebx,10 ) Q! N8 I! N. _; V
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/105 O$ B9 N" v0 ~1 M5 G+ {
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) ^1 N$ }/ H" H
cmp eax,0 ' l1 Y! i- F+ k& g+ J
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:9 m* S$ m2 u4 F& j3 W& Q: f9 p
mov eax, 4
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mov ebx, 1) g0 [- ^- v ?- B. X* v: A. \
mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]) w3 a& W# a% F6 i
sub edx, ecx: \& O7 _" E7 j6 J. A5 z
int 80h
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; Exit code
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EXIT:
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mov eax, 1
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mov ebx, 08 D- _8 M/ c' J/ O/ p0 Q: Q
int 80h
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; Factorial function using recursion. X6 Y. u% q9 _( ~# g( T' q
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( V8 V Q# p) w; r
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; Decrement eax and call factorial function recursively
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dec eax D4 v; t* N* P" G1 T
call factorial
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; Multiply the result returned in eax with the saved value of eax8 ~3 D+ b# w: ]; e+ b
pop ebx2 C6 S+ m2 g/ l
imul eax, ebx* c9 D5 I* [6 t5 Q$ ] a
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ret' p/ r! k' A O
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end_recursion:
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; Return 1 when eax is 0 (base condition)2 ?% [7 w" Z% g: h
mov eax, 1) l! \& D& x( O) P
ret

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