用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10* l, l6 b( k9 K7 `: s% W- V7 k
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;, B: {1 R* O8 R6 Z% W- [
lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg
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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) f: \- J* ~9 ~" C& \/ w: t
lenErrMsg equ $-errMsg ! V& S$ v( s& _' l7 d
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section .bss ;
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num resb 1
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result resd 1
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buffer resb LEN_OF_OUTPUT+15 b- I/ @& g' t5 @1 K0 ?% N5 b2 Z% y
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section .text ;
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global _start" r4 n# y5 J5 |4 g$ R4 Q: Z" q
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_start: ;
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mov eax, 4
mov ebx, 1
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mov ecx, userMsg
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mov edx, lenUserMsg
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int 80h: m# o- p( f. h+ B7 n
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; read user's input
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mov eax, 3
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mov ebx, 0
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mov ecx, num - C* E1 ?, F8 S" i8 v* ?+ E0 v! h
mov edx, 1 ; length of input buffer# \& x' [8 ~0 u( h
int 80h$ A1 o) q o3 C4 r! ^0 }
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mov eax, [num]
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and eax, 0xFF. Q* `9 U: z! h4 C" r1 N
sub eax, 0x308 ]( V5 x* a5 O: p0 [5 `! \: D
jl ERROR
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cmp eax, 10
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jl DO_CALC6 u c9 }3 _) \ C! T+ t) \' U2 ~. B
ERROR:
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mov eax, 46 h' ?2 D) v3 H' r C2 B6 N
mov ebx, 10 F/ a& U7 g* i6 z! V: Z8 u1 k' x
mov ecx, errMsg+ s3 f7 E0 ~; J& p1 r
mov edx, lenErrMsg- }7 `% u7 m* u* z5 I# Y5 G! T
int 80h
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jmp EXIT
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DO_CALC:5 @4 C) f1 t; z+ h3 Z5 S
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; W( f6 @' D2 Z1 D; R. K
mov eax, 47 \. N0 p$ ]& m
mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg! M/ _' X# u0 R: u1 t7 o# {
int 80h % n+ `1 N5 ^3 f# d
mov eax, 4
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mov ebx, 1
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mov ecx, num
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mov edx, 13 I9 m( ~1 O2 W4 R! l! t
int 80h " u2 E e0 W3 U
mov eax, 4) d& |' ^- N4 w3 C! D
mov ebx, 1
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mov ecx, disp2Msg2 d" D u6 p) V1 h% d; x
mov edx, lenDisp2Msg
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int 80h & L9 [$ p7 X& F% d. @
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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- k+ u2 h% @2 {9 Z
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10
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ASC_LOOP:$ l2 E& |$ [8 P3 Q3 o5 \& T
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 G& [' Q' r% H0 t& |0 Y
dec esi ; store characters in reverse order
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mov [esi],dl
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cmp eax,0 4 r( G) r- q a+ O
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT) D! X* x8 m; H% R' R- k
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mov eax, 4
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mov ebx, 1* X0 X- ^7 f' L# T+ ~- i
mov ecx, esi- ?1 T. k$ G8 K% q* d: M
lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx* @ |# }/ w. i: ]3 x! f$ @
int 80h
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; Exit code
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EXIT:
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mov eax, 17 j5 y" K# p. [) E+ z, O
mov ebx, 0
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int 80h
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; Factorial function using recursion7 Q6 D- D, j. V- U" J
factorial:
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; Check if eax is 0 (base condition)) _/ i# w3 ?' j1 ~
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 eax8 Q. ~' x8 z# y( s t g
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; Decrement eax and call factorial function recursively' {$ n% b1 Q# u( n4 I
dec eax
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call factorial- S+ P) L! G! k& T
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; Multiply the result returned in eax with the saved value of eax1 P( A! c/ Z; c# {+ D
pop ebx4 s+ Q' _: F2 z2 }. u
imul eax, ebx
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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/ P, q/ [/ e5 L) V' w
ret

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