用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;9 z+ L3 h' Z- [2 c ^5 i
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;" x5 v: A& F: S2 }, n8 i. T8 m. F, t
disp1Msg db 'The factorial of '4 N$ G! ?1 o6 `) K
lenDisp1Msg equ $-disp1Msg
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disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg 5 E& t8 Z& c7 t1 {
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg . T3 @ Y$ V9 {4 [
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section .bss ;
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num resb 1; ?3 I* B# ^' g2 O
result resd 1
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buffer resb LEN_OF_OUTPUT+1
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section .text ;/ d+ c/ d# m" L; h: W% P
global _start: J) O0 G# a9 S6 G4 J, w+ j
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_start: ;& \+ N, ~+ A* o! ?( v% r
mov eax, 42 |) Y$ _/ R/ ~+ ]7 Q0 G
mov ebx, 1 u# J0 O& u0 T5 ?# j/ i% b
mov ecx, userMsg" M0 n7 l9 f7 Y" {1 i3 M, w+ \
mov edx, lenUserMsg; b; t0 K1 N! a
int 80h
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; read user's input
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mov eax, 3" j& Y0 t) P: T! h
mov ebx, 0& Q" d! l! v% ~3 u1 {3 D& e) Q
mov ecx, num
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mov edx, 1 ; length of input buffer
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int 80h7 P3 I! G5 F( a0 T: E% `+ }1 b
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mov eax, [num]2 m( Y& h4 i; Z' J" i5 b" q4 g
and eax, 0xFF) w t; H' H* e# K% j
sub eax, 0x30
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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* @8 O" T6 K+ p3 u4 |$ U
mov ecx, errMsg
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mov edx, lenErrMsg0 D+ \& U. F8 {2 X: w
int 80h 4 y. l; O6 k" U6 h3 L
jmp EXIT( S$ s$ X2 k6 j1 h$ p
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DO_CALC:0 V1 E2 p5 f* Z7 ^, s6 @
call factorial0 `& c! A' B, _$ H
; The parameter is in eax. After calling, the result will be stored in eax.
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mov [result], eax ; Save the result* }- w3 N* k2 r: ?' o
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; print result& X2 ?7 I! }7 B$ l1 F
mov eax, 4' R! X6 c: i$ M& s- w7 \
mov ebx, 1# h! n' s8 p u v* f7 v0 G% n
mov ecx, disp1Msg; F/ _1 v1 K0 m2 u2 K" `
mov edx, lenDisp1Msg
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int 80h
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mov eax, 47 v' ^9 ?$ }' F' e) T$ p
mov ebx, 1- N: L. y* J2 n7 I
mov ecx, num
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mov edx, 1% I9 [1 u+ c6 f5 f
int 80h ! H+ p* J; @# N! I- N' `4 [4 {8 \
mov eax, 4
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mov ebx, 1
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mov ecx, disp2Msg
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mov edx, lenDisp2Msg
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int 80h
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; output number- O4 q; u* L- a' f" H# P
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
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mov byte [buffer+LEN_OF_OUTPUT],0x0a6 i- Z+ m9 Y( m$ {6 U! |) U4 [
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10
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
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add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
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dec esi ; store characters in reverse order! h; R: V3 E2 d
mov [esi],dl* L- z% ~: N' h7 S1 Z
cmp eax,0 ; i% g9 Z- ^1 F
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII: U1 t. y' l' T/ A( H: r
jmp ASC_LOOP ;ELSE REPEAT- ~1 X2 p! z6 F9 j* u( K r" O
END_ASC:
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mov eax, 4
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mov ebx, 1 r/ X4 h3 O$ f; L3 g9 s
mov ecx, esi5 z7 h* b% @! b' ]% l5 i& o
lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx
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int 80h : ~" K! \# c/ h) Q- n$ t" h
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; Exit code( r8 p! Q3 N9 j
EXIT:
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mov eax, 1- }! x2 A3 m$ ~" G$ t( t
mov ebx, 0- R6 t0 R& s5 j
int 80h
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; Factorial function using recursion6 x" @) M6 G9 P/ |7 q- p3 a* `: E
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$ T, F, F: ]/ O- ~
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; Save the current value of eax
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push eax8 P- q0 G( Z2 c1 C
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; Decrement eax and call factorial function recursively
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dec eax/ S! n( X/ ^, E
call factorial; {( R: x( ~3 ^
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; Multiply the result returned in eax with the saved value of eax
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pop ebx7 l1 F0 O, y9 P% F+ x
imul eax, ebx, y& o5 ?/ ~! A: }8 Z w
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ret- k y/ J5 P- ?9 d' Y
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end_recursion:7 t+ l" M; e( F! N
; Return 1 when eax is 0 (base condition)
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mov eax, 11 ~" a% ?8 Z P
ret

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