用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 103 _; X+ v" L* c
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section .data ;. K# m R' u4 e7 f* ]6 l
userMsg db 'Please enter a single-digit number: ' ;1 R7 V1 q) r: l4 E# B9 u
lenUserMsg equ $-userMsg ;9 ~# [ i$ A8 B+ Q# B. R$ L! c
disp1Msg db 'The factorial of '1 @4 d# D% x' X; Z1 S: X% O9 J
lenDisp1Msg equ $-disp1Msg ) i( |! }, K$ W2 F' p! s
disp2Msg db ' is '; t" f! n. [! n' x
lenDisp2Msg equ $-disp2Msg 2 P) X$ }0 t7 n
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 ;
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num resb 17 X3 M2 |9 o& \) a) ^
result resd 10 q' O2 F3 O6 K1 C+ |5 D) P
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start1 b' g4 F. x# q5 \0 Q7 N
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_start: ;: G( W$ Z4 a1 z" e
mov eax, 4; w* n0 P) u- D$ s
mov ebx, 15 \. m: {' r' |- R: k, A
mov ecx, userMsg* p) x$ H+ o. c) S: ]+ J0 J
mov edx, lenUserMsg/ I. s% D. a v* m9 ?1 B4 J
int 80h/ \5 e5 j: O- l- i7 r! ~# O( ?# |
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; read user's input% G5 e% H }" z. F# g9 @
mov eax, 3! I& C, }6 w" o5 G# X
mov ebx, 0
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mov ecx, num ) Y5 z0 |0 _9 ^+ _" V2 S+ ^- X8 f
mov edx, 1 ; length of input buffer
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int 80h& r. d3 E# k1 c q/ Q" Y8 Q7 x
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mov eax, [num]
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and eax, 0xFF" t' _; E* m+ ?: \0 r
sub eax, 0x303 z" o, n- D) j
jl ERROR" t, `4 S: c2 U8 z$ E
cmp eax, 10. q, i" M8 x6 L+ F$ M
jl DO_CALC: S2 u. s2 D% S! p3 n3 ?6 c0 F f
ERROR:/ Q; f9 O, F; E( i" T6 \/ H: }& D) V
mov eax, 4
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mov ebx, 11 `8 J" F6 v2 x9 \
mov ecx, errMsg# w' H' T# i$ B/ n D+ p1 e
mov edx, lenErrMsg
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int 80h
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jmp EXIT. \6 t8 C8 g# g! |+ k) g0 ^
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DO_CALC:( d1 w3 u0 O) k
call factorial& k- e3 ?# }3 {( k
; 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& e* v2 F# f6 Z# [: I
mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg$ u4 E, P' v% E: ]. c1 [3 \: B6 k. A
int 80h : |& V3 i4 d+ X! H& k6 j
mov eax, 4
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mov ebx, 10 C3 i5 ]% h3 @! \" K( e
mov ecx, num
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mov edx, 1
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int 80h
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mov eax, 4# b' B- u0 z; u6 q, k3 B+ \
mov ebx, 1
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mov ecx, disp2Msg& s; d; {, F! H
mov edx, lenDisp2Msg
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int 80h / _; W. W8 u# W" n/ ]8 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]& }* o6 z2 Y9 C2 F' {5 G
mov ebx,10
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ASC_LOOP:8 m1 U T! d2 N& _/ X: p% o& b
mov edx,0 ; clear dx prior to dividing edx:eax by bx' v! w9 y' ?. Q5 x
div ebx ;DIV EAX/104 G- @! j' e3 a8 C
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER 5 d$ a, X! m4 L, n
dec esi ; store characters in reverse order
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mov [esi],dl
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cmp eax,0 - C) d: ~! ^, p* I s* X
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII9 }+ e& d: x4 I7 x6 g; u
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:
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mov eax, 4. R q# r5 L9 Y- @
mov ebx, 1) ]: l# e# C0 l) q9 w
mov ecx, esi; y$ g) d2 ?' j: s
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
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EXIT:
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mov eax, 17 C J0 @0 y' I( O- `+ D) Q8 f4 W
mov ebx, 00 V3 t* @: f$ K' u
int 80h9 R4 ?' q1 L+ ~+ m% ]
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; Factorial function using recursion% I) M9 L6 S: I' ?
factorial:
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; Check if eax is 0 (base condition)& H, `( v* E" R( d
cmp eax, 0
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jz end_recursion: ?5 @+ e' j! |$ R: I/ [& K7 F
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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
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; Multiply the result returned in eax with the saved value of eax
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pop ebx O. L% k4 n- e, J- F
imul eax, ebx
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ret8 n( v4 @$ s& F2 h
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end_recursion:
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; Return 1 when eax is 0 (base condition)% J( m8 w: \5 E5 f
mov eax, 1
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ret

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