用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;5 }# K K( C; x% `
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '7 @- h7 n) H8 U6 n" I$ f, {
lenDisp1Msg equ $-disp1Msg ! Q8 s) u3 \; F- _. A, o5 w5 z
disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg ! t2 r' [+ R) }- d7 z
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg 2 @ q. L7 o, ?5 W B3 m
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section .bss ;
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num resb 1
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result resd 18 B- v3 @# t+ m, W' t3 H
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start
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_start: ;
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mov eax, 4
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mov ebx, 12 d2 L; v8 L( k- G
mov ecx, userMsg
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mov edx, lenUserMsg7 G1 t8 w' B! A. C
int 80h, Q- v0 f7 }& j* |
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; read user's input( T& u) K$ s" O, V% [
mov eax, 3/ V# k' O( `. d/ s9 r
mov ebx, 0
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mov ecx, num
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mov edx, 1 ; length of input buffer( V" U# P! |3 s
int 80h! c. X( `+ U; `) P: y! q* c
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mov eax, [num]
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and eax, 0xFF
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sub eax, 0x303 y2 S/ e2 y4 _9 e6 o6 _
jl ERROR5 I6 n7 W1 n0 T9 u. k) Z
cmp eax, 108 r# T! W; f3 b2 S) ?
jl DO_CALC
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ERROR:
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mov eax, 4
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mov ebx, 1! q3 m& v6 z& n! G5 T: [
mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h , k0 V( y1 C$ F4 K v1 y, u) c
jmp EXIT% ?# u X& s( T6 E
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DO_CALC:
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call factorial# z. J* v5 b4 Q% Y/ l3 v; W& i
; The parameter is in eax. After calling, the result will be stored in eax.( J, D+ Z) G" R
mov [result], eax ; Save the result
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; print result3 y. `. K5 G# }3 y$ V6 h
mov eax, 4 o- B/ y- w, `" i$ @
mov ebx, 18 _5 g/ C# I/ I6 E9 @
mov ecx, disp1Msg
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mov edx, lenDisp1Msg
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int 80h : f {! H% N+ B* m: L+ N
mov eax, 4
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mov ebx, 1
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mov ecx, num
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mov edx, 1
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int 80h
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mov eax, 4
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mov ebx, 1
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mov ecx, disp2Msg# p7 Q+ X: l+ w( X3 W' K1 D
mov edx, lenDisp2Msg1 R# \( a& V% G. `8 F2 n
int 80h
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; ^( s3 J# @ y% m0 G+ N) e
; output number, `4 f: V( r# d5 Q* {9 k7 B
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY @. d# M7 U- a: N+ E
mov byte [buffer+LEN_OF_OUTPUT],0x0a- V9 W& F/ P2 M
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 ( i+ I' \) d8 C- @
ASC_LOOP:' W3 x! U( _' l0 m4 y2 [( |- _
mov edx,0 ; clear dx prior to dividing edx:eax by bx9 G. A* s% z" [' O: ^0 K# @- D
div ebx ;DIV EAX/10- X) K ~( V5 e2 z
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 " G# b$ Z& w1 g; Q% C, v& W) B
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT# G+ `1 \4 ~" r& R; _5 r( a
END_ASC:+ L1 d- m8 f% q$ ^
mov eax, 4: U2 l; I# L# G9 ]
mov ebx, 19 O6 Z T. H4 H# S: ?
mov ecx, esi) H; w% k9 O/ V& @9 z' f
lea edx,[buffer+LEN_OF_OUTPUT+1]4 q* S: \5 j) V( g, G
sub edx, ecx9 ]0 e! A7 N: _4 H4 p3 u% I
int 80h . N, N) A, t; V) R
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; Exit code
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EXIT:3 }! |, y8 s; w
mov eax, 1
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mov ebx, 0
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int 80h' F- u) x- Z( G4 a( ^
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; Factorial function using recursion
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factorial:
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; Check if eax is 0 (base condition)5 j% J; q8 K3 W0 ^/ F
cmp eax, 0
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jz end_recursion
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; Save the current value of eax, J; N. c w$ y$ W; d4 C f
push eax
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; Decrement eax and call factorial function recursively
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dec eax
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call factorial
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; Multiply the result returned in eax with the saved value of eax( k9 h/ X* f" v
pop ebx7 ^! u2 Y3 M+ }
imul eax, ebx
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ret6 S2 W3 A5 i$ r. Y# Y
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end_recursion:) C ?5 v7 P1 @5 B6 @. T. T
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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nasm -f elf factorial.asm9 s% U& L4 g% u+ `6 V& w+ m* d2 u
ld -m elf_i386 -s -o factorial factorial.o
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./factorial& y7 z. U6 d! x( O9 t

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; Factorial function using recursion) X: Q( l# U6 y8 R( q1 R
factorial:7 ?. t) F: @% }
; Check if eax is 0 (base condition)' S4 c$ X' g* x$ o d$ e- e
cmp eax, 0
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jz end_recursion6 R' k" }, o* I
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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 recursively4 p2 Q8 W; T" P1 {) Q
dec eax0 e% I, P/ V, P- `% q( k, X
call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx
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imul eax, ebx
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ret0 Y- [* h- x s+ h
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end_recursion:7 Y% j! a( g4 c9 [' i: O
; Return 1 when eax is 0 (base condition)4 B3 H$ ~! r6 ^) h2 c# z
mov eax, 1
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ret

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