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: ' ;! @# `. P3 h3 h/ s- L
lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg / L# w9 C: E c8 `2 \1 Y4 C
disp2Msg db ' is '0 n1 @* B: q9 b# D
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 $-errMsg
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section .bss ;' u# h q& o1 R2 x
num resb 1* w) D. s9 T" k( M8 M# ]
result resd 12 V+ k1 Q7 ?2 [' M/ B: }, g
buffer resb LEN_OF_OUTPUT+16 Z$ T% ?1 H8 |- Z) {; e! K4 [
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section .text ;
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global _start' r: ^" ~. X& a% W/ I$ \
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_start: ;5 U) G" M& {& g6 k0 F
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg! l! I1 Z) w7 X# i) i! L; r2 `
mov edx, lenUserMsg
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int 80h& l& A; h5 R6 ^
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; read user's input( Q% [" Y' j; a/ J% S
mov eax, 3
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mov ebx, 0) k3 H# d4 b* u% {& r
mov ecx, num
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mov edx, 1 ; length of input buffer
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int 80h
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mov eax, [num]& i2 }, t g% D8 z1 e: f0 P0 w
and eax, 0xFF2 O+ u3 {3 B3 ^$ a: V* p
sub eax, 0x30. V/ V& p8 b) L2 `$ N- U9 Z' z- F5 g$ r
jl ERROR- R0 v& l E/ y! ^% q/ R. e* W
cmp eax, 10( \5 K) d0 o% x. ^- f" A3 R
jl DO_CALC
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ERROR:; d& D, R6 z; b8 ?
mov eax, 4
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mov ebx, 1: d$ i5 Y; j4 G5 |) z3 D
mov ecx, errMsg
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mov edx, lenErrMsg8 g: P! j, L9 {7 `
int 80h . T% ~5 I v8 Q9 m, p6 o w: q+ f
jmp EXIT
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DO_CALC:
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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
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; print result
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mov eax, 4+ B' w" Y+ p$ _; [2 x
mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg
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int 80h & s, h, j- V) R, f( G/ {( V. h
mov eax, 4
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mov ebx, 1
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mov ecx, num
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mov edx, 1* a! j, U+ l; y# y% |5 {
int 80h 0 y) D( {& {; p2 Z- S
mov eax, 4& F$ A, L; Z/ u- q P
mov ebx, 1+ O+ Q& u$ s/ j" Z
mov ecx, disp2Msg
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mov edx, lenDisp2Msg
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int 80h 2 C& d) c6 L; D1 L( s
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
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mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]2 b* n5 F2 B# O2 y' l3 S; N
mov ebx,10 ) o* D9 o% h/ a* S9 E# G$ F
ASC_LOOP:0 K0 P' {8 _1 O; g$ x- n
mov edx,0 ; clear dx prior to dividing edx:eax by bx* m. ?0 @# ]* V2 Y; K
div ebx ;DIV EAX/10
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add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER ) W0 e; f" E! E
dec esi ; store characters in reverse order
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mov [esi],dl
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cmp eax,0
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jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT$ f; h$ m3 q/ o5 y% V& b) ~/ a1 f
END_ASC:
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mov eax, 4
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mov ebx, 15 M" k, g- i, q
mov ecx, esi
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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$ i0 o6 B1 O8 J, X
EXIT:
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mov eax, 1+ n& C0 L3 K' _- W8 v
mov ebx, 0; P) J9 m. p( \! c( X# v
int 80h! G0 b+ z- P9 E
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; Factorial function using recursion
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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
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; Decrement eax and call factorial function recursively, U3 {' M0 Q, t) T
dec eax% ^+ p* @: y' c& M
call factorial/ D- V- o. ]- {5 |3 p$ U
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; Multiply the result returned in eax with the saved value of eax
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pop ebx4 ?) V8 W) T8 K ^
imul eax, ebx
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ret
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end_recursion:7 J" S. O/ o5 m# @
; Return 1 when eax is 0 (base condition)- X6 r4 y1 R4 R. d! c" @
mov eax, 1
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ret

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