用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;2 [8 T" n7 n- v2 h8 Q ^7 E. X+ K3 l
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '- D) J- p5 N! t" d
lenDisp1Msg equ $-disp1Msg ! h( C6 Z; W' ], q
disp2Msg db ' is '
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lenDisp2Msg equ $-disp2Msg 1 q7 a! v* q; |. j3 t$ o
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a z: {0 t& n/ m7 V6 i
lenErrMsg equ $-errMsg : p: K( G2 u4 [ I
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section .bss ;- D& H6 H d: w
num resb 1& [2 i! E' E0 R. X
result resd 11 e" q0 e) ]% X5 n6 r. ]1 Y3 K
buffer resb LEN_OF_OUTPUT+1/ ^" m; b# G( b1 b4 \; J c7 b
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section .text ;( O% v- z% g5 K8 `2 d
global _start4 _$ i9 f0 x- j: d/ h8 j
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_start: ;$ h7 G$ P* p. u! L6 c* ]. e
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg: y1 |8 _- n1 _/ E5 m9 n
mov edx, lenUserMsg# w$ I5 O, g; V# r$ n, X7 q( ]
int 80h
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; read user's input
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mov eax, 3
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mov ebx, 06 h7 A# N5 o- x( I& Z, \1 e6 e) M
mov ecx, num 5 R6 ]1 J% w% p- B+ P
mov edx, 1 ; length of input buffer2 B" f5 e1 u- F
int 80h; N& B5 G% D' `+ g6 E' a
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mov eax, [num] Y3 T' n- G8 f8 D! g8 c
and eax, 0xFF
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sub eax, 0x30
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jl ERROR$ E' h& M3 G+ p
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
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mov ecx, errMsg) ^7 m5 o& W- p- f; y3 I
mov edx, lenErrMsg6 M0 U# p& T% N Y- ]
int 80h 8 V- a' v; @. k6 Z7 F0 r& K# c" [* [
jmp EXIT' k7 J6 F5 d- c8 V- |8 g
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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.+ X3 }' O- Q8 {2 u) q$ t4 z
mov [result], eax ; Save the result, j- V+ ]# Q: p
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; print result
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mov eax, 4
mov ebx, 1
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mov ecx, disp1Msg/ U9 n" C8 E, C: C2 x
mov edx, lenDisp1Msg
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int 80h
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mov eax, 4
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mov ebx, 13 c9 J# X% ~, u1 s. Q& \
mov ecx, num& ^/ V. y. L! d% T1 L) w
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* x5 u4 z+ @7 O; `; @7 v) w1 @
mov edx, lenDisp2Msg1 _8 B- E/ }' r
int 80h ; v& q6 M! ?! B, }$ C
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; output number! D7 p, B+ |0 n( \4 E
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY& p5 w' \! ?. E K
mov byte [buffer+LEN_OF_OUTPUT],0x0a) w, i4 W! L9 O- ^- I
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 ! |( m$ ~3 u; { N; `+ L/ j
ASC_LOOP:' O* i6 f" Q! Y7 I2 E# u: r
mov edx,0 ; clear dx prior to dividing edx:eax by bx L' \/ U0 U9 y. O. A& m5 C
div ebx ;DIV EAX/106 z4 f8 I9 \0 U) A
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER % p* `! U+ H4 I: n+ R Y6 O# n
dec esi ; store characters in reverse order |7 K" C. U' Y& M( h" Q
mov [esi],dl/ T( Q( f; j0 }7 f7 h3 m* ]9 j% }
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 REPEAT7 N+ z5 g% ~. v, o+ F" ~/ w! E
END_ASC:
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mov eax, 4+ J ^% A. q) x$ B
mov ebx, 1
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mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx$ w* E* Y" V( P" O6 S- ? R
int 80h * d: C- Q( X1 K y9 U, P, F
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; Exit code
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EXIT:. A% N" i4 W3 T% j; b
mov eax, 1
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mov ebx, 0
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int 80h; Q" ]4 S$ @; e7 f
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; Factorial function using recursion2 s) z% u7 }7 C; F" S7 w7 n& \
factorial:, P) ~- {# L' G2 a% b, m
; Check if eax is 0 (base condition)/ X0 F; T4 d' z' w4 ?6 d
cmp eax, 0
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jz end_recursion, R6 e9 D& \# _8 E
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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
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call factorial- P( ~6 u G; F
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; Multiply the result returned in eax with the saved value of eax. {; e" @* P) {
pop ebx! { U/ h( M! R& H9 j" A
imul eax, ebx& ~ n4 _" R$ @: E1 x
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ret
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end_recursion:6 c. p2 Z( K" ^' e4 w- M% ~. T
; Return 1 when eax is 0 (base condition)( m) X% {' n! s, Y* c
mov eax, 1
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ret

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