用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;! z5 b3 q) }/ ~6 ~5 E
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;- K1 ^! `/ h6 M/ @& O
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg 8 A" i: C9 B: s }1 g$ |6 x7 y& ^5 }2 }
disp2Msg db ' is '/ W- E [, k% |- A" L/ j
lenDisp2Msg equ $-disp2Msg 0 J0 Z8 D0 G4 Z7 F: C5 Y) H
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a% h9 u6 n" d, c& \+ b9 c
lenErrMsg equ $-errMsg
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section .bss ;9 v7 B7 s% f! \- @5 r# |' m
num resb 19 E, y+ N1 q/ P! I
result resd 17 S; c6 \+ @7 D7 y x# l
buffer resb LEN_OF_OUTPUT+1 P n$ ~5 ~8 B8 F$ t% y
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section .text ;# e& i, w! X! Q0 p3 v
global _start" r% z9 A$ E- H; b
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_start: ;
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mov eax, 4& ^- j* O8 t" ^- D: k4 H
mov ebx, 1" i) U; C- U; R! g
mov ecx, userMsg
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mov edx, lenUserMsg# |+ o5 u# C6 \1 U! q/ i
int 80h2 G& L9 n4 `& D% I# e; k
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; read user's input
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mov eax, 3; ]! B0 \$ G: C- X
mov ebx, 04 t% J- {; w2 d C" s |! u' _
mov ecx, num
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mov edx, 1 ; length of input buffer
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int 80h k3 I+ F( [* o3 J
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mov eax, [num]+ t7 S8 | {' R3 ?1 \; g
and eax, 0xFF5 [1 {# r/ J. \( D9 t7 @% _9 T6 e+ A
sub eax, 0x30# y- V2 B3 l3 g* K; D' W' n: d
jl ERROR
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cmp eax, 10/ j6 _) F+ o3 ~4 y8 r
jl DO_CALC
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ERROR:
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mov eax, 4/ q& }5 A) V( J% l$ N
mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h
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jmp EXIT) R$ H+ ?2 c, I' u _9 \0 ^7 k
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DO_CALC:
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call factorial# ^) E+ ~9 d2 w, M7 B
; The parameter is in eax. After calling, the result will be stored in eax.: R$ ?" x8 n! C. Q: C4 ^
mov [result], eax ; Save the result
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; print result: M/ F4 e1 V$ q( D
mov eax, 49 N6 l% [. S1 h; L+ s
mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg+ ]2 y$ h; q- C
int 80h ' o/ u" t y% O, x0 F- U* B' I
mov eax, 4
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mov ebx, 10 O# P9 d, W3 V
mov ecx, num
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mov edx, 1
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int 80h
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mov eax, 48 j' }& n2 N- @
mov ebx, 17 ~ G. \5 D, l v$ ^
mov ecx, disp2Msg, S* y5 }, A- t: l. G; |" w
mov edx, lenDisp2Msg
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int 80h U6 w5 T* i; g) U+ ^5 \) ^3 U
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; output number0 `6 ^& a: P# i, t4 L t
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY8 f, `3 x; v6 K9 |- c1 T4 ^
mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 - m* E, k$ d# m7 e0 u
ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx
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div ebx ;DIV EAX/10" |- T2 S) q" @
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
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cmp eax,0 7 n* [- L/ S: `3 @, f
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:+ A' w% N! t0 j. m6 D: z2 g$ r
mov eax, 4# b; d+ {; ?3 v$ r) z8 ]. {
mov ebx, 1
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mov ecx, esi) K5 V+ D* {; b7 r- O8 m3 L
lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx" D* X) S# x$ R6 O5 P. }" z
int 80h ) u: o, D# M- _) w
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; Exit code @9 m j7 H# e( u( |- P/ f8 q
EXIT:
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mov eax, 14 p& a3 m% \( b6 L
mov ebx, 0
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int 80h
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; Factorial function using recursion( {9 L, P: i8 P! Y9 z' |, G. V" Y
factorial:
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; Check if eax is 0 (base condition)& |* \; X8 v7 r' T/ c- L+ J }
cmp eax, 0' X" M: \5 W0 x6 ^5 h- J3 a
jz end_recursion, {6 s% V$ V! _ |1 T3 p& \
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; Save the current value of eax" ?1 h u7 s) ~; F/ O% \# {9 H
push eax+ t+ ?9 w( Z0 f! l- z" W
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; Decrement eax and call factorial function recursively9 }! H+ g& A+ t) ?7 T. P
dec eax
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call factorial3 q' o$ D* i/ ^! H4 x. D( v
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; Multiply the result returned in eax with the saved value of eax
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pop ebx& P% M+ V, t/ e' z! R6 o
imul eax, ebx
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ret0 m5 w% t* |/ m( a
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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