用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;, D! E Y. v# H* Q
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;2 c! h7 P* }$ k' q1 L
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg : a! T% b% g7 o9 {
disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg 0 X, X: V% V' p
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg
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section .bss ;2 _% a3 B8 A" m9 t3 p- ~- q) Q* t# F
num resb 1/ Z) j i8 G# q: ]$ o8 d U
result resd 1" D( j/ D7 M: ~0 }' w, x4 x
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start3 ^- r( n) Z( X+ }" c
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_start: ;8 @6 `+ t0 x* u( q
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg- V4 ^$ G" A7 G3 l0 {
mov edx, lenUserMsg2 R! [0 q6 S2 J+ i8 P0 _2 z
int 80h: z' @6 f; c! h/ ^$ P
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; read user's input
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mov eax, 3- J! X% c1 G7 q: l% f* h) S9 L$ {* w6 f5 a
mov ebx, 0& q0 a( M# U* h3 F" I3 i
mov ecx, num
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mov edx, 1 ; length of input buffer
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int 80h- a' ^6 L' ]& M. s A
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mov eax, [num]
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and eax, 0xFF+ |; r/ Y/ u/ ^! B( D& s/ O
sub eax, 0x30- P, ^4 \/ [6 B# [
jl ERROR& P3 ]$ x0 H% ?" ]. D
cmp eax, 10
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jl DO_CALC! T; X, v. Y1 J; j# K* D
ERROR:
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mov eax, 47 ^. ^1 i7 A; [" {% d' A/ K
mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg9 _; W, r& d0 T8 u a
int 80h 5 e: |8 @. y3 l' L& r
jmp EXIT- l; U8 P8 M) R% I* c
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DO_CALC:
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call factorial% ^8 T, i: b0 h4 T9 N* k2 \8 t0 z5 P& I
; The parameter is in eax. After calling, the result will be stored in eax.* |5 x2 x$ s* Q8 K( a9 k/ I
mov [result], eax ; Save the result' E5 B8 V9 S8 W3 i2 O
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; print result# }- L; ~$ J* q) c. ^
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 - ]' \$ C: q9 f0 E( _8 _
mov eax, 4
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mov ebx, 1
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mov ecx, num; v) f m5 H& N+ z+ p
mov edx, 11 W/ b. k; t+ _8 J# E+ {6 F/ R
int 80h
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mov eax, 45 [* y( L3 ~7 V! v
mov ebx, 1
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mov ecx, disp2Msg6 b4 G, L: G8 k* ^. ^! o
mov edx, lenDisp2Msg
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int 80h O7 |1 [& I- M* `( z% `" Z2 l/ c0 P
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY' K0 s3 l3 A6 [; m$ @% t; S9 G
mov byte [buffer+LEN_OF_OUTPUT],0x0a' W1 X. D. P( O! c
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 2 m2 `; Z* O6 a3 _8 l6 G. V/ |
ASC_LOOP:! L, i" @% A5 H
mov edx,0 ; clear dx prior to dividing edx:eax by bx6 w' U7 v- \& z9 ~! I, I3 c9 \
div ebx ;DIV EAX/104 f8 F2 A" E- C9 ?- L
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER ) y8 p9 {2 \3 a0 E& v
dec esi ; store characters in reverse order
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mov [esi],dl, N/ X; c0 S- ~% n
cmp eax,0 ) p( ~: g0 _4 t% |( m
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT7 v! w* @9 x( ^& M9 C: J* V
END_ASC:. p$ M6 f& }* O7 N4 K" N
mov eax, 4
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mov ebx, 1
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mov ecx, esi* X4 e. @. o$ [ J) }
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
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EXIT:0 N- d+ j( z1 s/ l5 E. R' E% X
mov eax, 1$ Y8 b/ q q% h" w( b; P
mov ebx, 0
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int 80h$ c( d6 k O: t! r$ _# Y
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; Factorial function using recursion
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factorial:8 F% F3 U9 ?2 m. S x. [0 Y
; Check if eax is 0 (base condition)
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cmp eax, 00 r* u- B# y8 H( [7 }9 U
jz end_recursion
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; Save the current value of eax
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push eax
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; Decrement eax and call factorial function recursively
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dec eax {1 E1 b' j+ Z m- ] T
call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx! W" B% V. |! _, n, W
imul eax, ebx6 v6 o; t6 x) o. g$ Q1 w5 K- k
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ret
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end_recursion:8 ? H: b! f4 U- n8 x. H6 q( O
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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