用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10- g0 k0 o" M7 N4 F6 D; I& y. a
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section .data ;+ w3 F: J4 D2 G
userMsg db 'Please enter a single-digit number: ' ;$ C- O4 N5 o4 u, ~' d
lenUserMsg equ $-userMsg ;" ]/ _. Y: R4 h) T- w
disp1Msg db 'The factorial of '1 ?& L9 P0 Y& J) _% O L; e$ C7 b
lenDisp1Msg equ $-disp1Msg 8 c+ ]7 @( i/ ]* r6 j4 i0 W6 W
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 $-errMsg * }) D; o7 T0 k- F) q. m
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section .bss ;( k( {. N# Q" p
num resb 1
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result resd 1
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buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start
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_start: ;- H h3 z/ H2 o8 m
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg# }3 `$ g+ c& Q, K+ ~9 d4 ]/ X/ a* N
mov edx, lenUserMsg
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int 80h4 u* J Z) x( ?+ h
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; read user's input. q, ?2 v1 b) G, J* Z
mov eax, 3& M5 K' |8 e7 f- \% q6 a2 C1 g+ y
mov ebx, 0
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mov ecx, num 7 E: X$ L0 D, [$ z) U* C
mov edx, 1 ; length of input buffer! D% k5 s4 g) f) J( q2 D9 d
int 80h
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mov eax, [num]
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and eax, 0xFF% T) Q, D m9 F" f. N
sub eax, 0x30
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jl ERROR" d/ M, r# W* h
cmp eax, 10
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jl DO_CALC/ U) F# o7 F, ]4 o: I( H
ERROR:# ^% X2 V, ~" {' Y8 P9 K
mov eax, 4! `& q0 f8 v' L5 P1 X! x9 V- ?
mov ebx, 1
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mov ecx, errMsg; o, G+ f$ {) ^- S4 q
mov edx, lenErrMsg% ?. A) X8 B' z6 t1 M2 M
int 80h - O4 L9 k7 ^6 S
jmp EXIT
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DO_CALC:/ r6 [6 x e6 E2 A* i7 ?; S5 s
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.+ B; \" P/ Q1 Z- s
mov [result], eax ; Save the result# G' k+ h2 B% P! K K
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; print result+ w7 P4 q! J" T/ F
mov eax, 4
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mov ebx, 16 g; Y4 e$ f* t' j
mov ecx, disp1Msg
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mov edx, lenDisp1Msg5 w" S! @9 k' _+ F, o3 |
int 80h ' Q4 ~: _3 c; \
mov eax, 4
mov ebx, 11 W* P( l7 R9 h/ g
mov ecx, num3 W* H; E' G! d5 z: {! ^3 I
mov edx, 1
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int 80h
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mov eax, 4
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mov ebx, 17 ~' k D, ]' }6 Q
mov ecx, disp2Msg
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mov edx, lenDisp2Msg
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int 80h
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY: A/ `" S! l) C
mov byte [buffer+LEN_OF_OUTPUT],0x0a, t2 T" i7 }. O% y* p! L
lea esi,[buffer+LEN_OF_OUTPUT]3 z" T, k4 J. T6 n
mov ebx,10
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ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx6 F( C+ H5 Z1 I9 J* k6 R
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
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mov [esi],dl' y6 S4 q, Y& X; \2 C& i
cmp eax,0 0 }9 |$ n1 @, W' P' A. @- f$ U
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII$ i' J- Z4 I- a9 x* D
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:+ H8 {% x1 Z5 r; m- y; @1 B
mov eax, 4& h/ W i3 p S( q: k* @0 q
mov ebx, 1/ K f3 U8 h! d
mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]( T3 e e3 |% D7 C
sub edx, ecx
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int 80h
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; Exit code& z; v& I5 C; c- C
EXIT:9 u; G2 v8 g, ]: l$ K: B. {# `
mov eax, 1' r+ l4 V! Y6 A# w' G5 s. b& C
mov ebx, 0/ F) e) i9 F9 O7 S& e' u A8 s, A
int 80h2 F1 {" ~$ }' L$ J: _3 |- b8 @
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; Factorial function using recursion
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factorial:* z& o) Y% W; y b2 v
; Check if eax is 0 (base condition)/ A% }3 B! k" i
cmp eax, 0
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jz end_recursion) A/ y H2 A, x/ \! T6 ~: f2 `/ L
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; Save the current value of eax2 w; J. Q. U, o" K
push eax, o+ x0 S) M# @& [+ z: p
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; Decrement eax and call factorial function recursively2 k# ?: B% A6 |, K; E/ M. H1 S
dec eax. W- j/ X; S! t
call factorial
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; Multiply the result returned in eax with the saved value of eax0 M- R. {; \: K" @( L# i' V! y m
pop ebx
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imul eax, ebx
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ret# K7 N% Q9 [( Y+ y
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end_recursion:; R v8 ?) ?8 W q: {( d1 Q# p
; 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.asm, j! d/ P( ^# m% U
ld -m elf_i386 -s -o factorial factorial.o
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./factorial
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; Factorial function using recursion0 S; H* M. D& ^3 D0 Q2 U6 r! g
factorial:
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; Check if eax is 0 (base condition). u! \4 a. G0 i
cmp eax, 01 A4 j. C- g) K/ u
jz end_recursion
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; Save the current value of eax8 i3 y' Z6 F# M9 Q* C
push eax" U" Z" n( Q' ?5 q, H( H2 }
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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
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pop ebx" g% e) u; G' R! K4 F
imul eax, ebx$ l1 y, O/ R5 G; |
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ret
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end_recursion:
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; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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