用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;
userMsg db 'Please enter a single-digit number: ' ;; i) ~& X& m7 l) s: \9 L
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 '4 b' b8 [- w4 k4 X! Q) R2 x
lenDisp2Msg equ $-disp2Msg , h1 g5 I& b7 F
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a1 s0 [! y* R' [- B5 ?$ V
lenErrMsg equ $-errMsg
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section .bss ;& j e1 I5 M: N& l
num resb 1
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result resd 1/ ^: y' [$ ^3 [4 X! _: e
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start
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_start: ;
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mov eax, 40 A u+ _5 T b
mov ebx, 1
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mov ecx, userMsg1 S& L1 _- I) M
mov edx, lenUserMsg
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int 80h
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; read user's input
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mov eax, 3- g; E4 H- {' q" Y
mov ebx, 0& w( s, o" c) e; \. q
mov ecx, num / a! x, B% Q# _+ {' T
mov edx, 1 ; length of input buffer' H# l9 R# H& l, v; `2 G
int 80h
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mov eax, [num], ?# `; F N) S% g7 R6 e" l
and eax, 0xFF
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sub eax, 0x30
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jl ERROR2 f8 f. b+ T' Z5 {8 T# ?$ r
cmp eax, 10! A! k7 G3 T' ~
jl DO_CALC9 u* R% S1 u7 [( J
ERROR:- K) e$ t& z4 S3 l8 D- X
mov eax, 4! L, C$ C/ q7 w8 b1 Q7 Q4 z* o( ^
mov ebx, 1' U8 s- G/ u9 _! Q" @- O
mov ecx, errMsg
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mov edx, lenErrMsg
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int 80h R8 K% V0 E7 `
jmp EXIT3 E2 X) ?- y5 K( C) m
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DO_CALC:
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call factorial }9 d# k/ S$ J
; The parameter is in eax. After calling, the result will be stored in eax.
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mov [result], eax ; Save the result1 v! [& E8 Z6 f3 z3 l4 F* O. O
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; print result3 h, b+ |6 ?+ B/ d4 c
mov eax, 4
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mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg+ [9 E m8 e8 q7 ]
int 80h
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mov eax, 4* i( a0 k% a: Y: a; I
mov ebx, 1( D3 K8 l2 s; p# G/ l. n
mov ecx, num
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mov edx, 1
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int 80h
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mov eax, 4' |) c" b7 {* S6 S0 i
mov ebx, 1; r) W. B" r" z5 N
mov ecx, disp2Msg6 e) o! y: [: E# v' U1 W7 w7 Q- p
mov edx, lenDisp2Msg8 H" L/ F4 {" R5 q3 X6 D: y3 r9 b
int 80h ( ^7 ~ n8 j$ B% y7 W p' u1 P
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY8 n( a% Z& ~0 N# _" Q- t9 @! P+ u
mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]0 t% E7 } R: n4 a, j6 s
mov ebx,10
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ASC_LOOP:; q a' I. i6 S" r' Z: t
mov edx,0 ; clear dx prior to dividing edx:eax by bx
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div ebx ;DIV EAX/103 O6 h9 y9 x( G$ t0 ^
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
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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
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END_ASC:
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mov eax, 4
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mov ebx, 1' b/ b0 H3 |# T3 a
mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]: b; x' ^& X4 v6 p$ B
sub edx, ecx
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int 80h , f* n. ^) C* x# V t
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; Exit code7 X: T( m3 `9 S" W, z
EXIT:4 V5 p. T d& |: n" Z
mov eax, 1
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mov ebx, 0
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int 80h. U, G) t: I$ j2 o0 t5 _
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; Factorial function using recursion3 I! ?" \# x0 l
factorial:" ?% L7 ^$ H( y' @2 Q, r& E' ^
; Check if eax is 0 (base condition)
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cmp eax, 0$ o; b3 {! K- y/ ?8 `$ q2 I
jz end_recursion
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; Save the current value of eax% Q: {4 F( U# S; e: P# c( x
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- b& _2 l& A9 d5 [, x! p
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; Multiply the result returned in eax with the saved value of eax) r6 P8 w8 ~3 c. F
pop ebx
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imul eax, ebx' U3 V' `, ^- ? ]9 ~) H3 R
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ret4 ?# ^, G: b, U0 g, ]; Y( l
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end_recursion:1 H1 H$ ^3 \7 _
; Return 1 when eax is 0 (base condition)
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mov eax, 12 f; C$ x$ @5 G7 F! n* n0 x
ret

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nasm -f elf factorial.asm g7 O$ |3 s; F' g
ld -m elf_i386 -s -o factorial factorial.o2 g3 M) p' h; B9 Z0 v4 H2 v
./factorial
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; Factorial function using recursion" z8 @* J8 l) K% K. o) d
factorial:
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; Check if eax is 0 (base condition)
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cmp eax, 0" _$ o8 D# N8 i7 I7 s l
jz end_recursion3 V! _7 Q3 q8 S
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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( d, e/ d/ {' X
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; Multiply the result returned in eax with the saved value of eax
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pop ebx
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imul eax, ebx" t% c) U- I0 f: K5 ]
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ret# v$ Y7 o1 |9 J9 S6 y* E
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end_recursion:- w: _- Q" U( v
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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