用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;9 T$ D5 Y& K% }& [& Y( F* J
userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg : t/ @$ {) W5 d* x, u; I5 i. ~. v
disp2Msg db ' is '8 e# K/ r6 j2 ~+ C7 _' J
lenDisp2Msg equ $-disp2Msg * u8 S* T `9 \" B1 U# Z
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg ( M* i1 z! ?! J2 Z& V3 t
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section .bss ;
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num resb 1
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result resd 1
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buffer resb LEN_OF_OUTPUT+1
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section .text ;/ z3 D% Y2 r% c7 q9 d8 ^
global _start! o! ~; i5 A2 ^' H
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_start: ;: G# s0 g! R& n. n
mov eax, 4
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mov ebx, 1. \1 i0 D1 q4 j5 V0 ^' O: y3 M
mov ecx, userMsg
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mov edx, lenUserMsg' l2 Q0 {: F: t2 d/ `! f
int 80h
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; read user's input
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mov eax, 3, x. a5 ]& L9 B9 y% Q
mov ebx, 0
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mov ecx, num + F: N$ q2 n' D, @9 l
mov edx, 1 ; length of input buffer
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int 80h! M2 P% `; v8 ]' W. K# V
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mov eax, [num]5 _2 {) A, h8 B; q# P \- Z$ p. w
and eax, 0xFF1 K4 j# n a2 B* x0 c; B/ P
sub eax, 0x30
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jl ERROR! } z; `6 G' C9 z4 c3 e7 f% J
cmp eax, 10* j6 o0 y5 T, i0 _
jl DO_CALC
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ERROR:) K% l1 f* W8 x: d: ?. D% \' ]
mov eax, 4
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mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg5 o' e1 \% k* X: f; v
int 80h 6 a- v4 h$ d& e( |/ g
jmp EXIT0 |2 Z! P, c+ {
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DO_CALC:) Q; S6 O, P4 o: q8 h' k
call factorial( Z; t2 p( Q! o6 L1 M" M
; The parameter is in eax. After calling, the result will be stored in eax.) b( B$ `- V" @ g2 c5 b7 F! ]. ?
mov [result], eax ; Save the result# \- e/ e( `$ C- P) Q: j' o
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; print result5 F, `% }. m- f/ M( j
mov eax, 4$ ~( P& H* s6 o* r5 `8 e x1 f
mov ebx, 1
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mov ecx, disp1Msg- k0 Q- ?) H0 A% u5 M+ M- c: Z+ {/ G
mov edx, lenDisp1Msg
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int 80h
mov eax, 4
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mov ebx, 1
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mov ecx, num" B# C, g# b2 i2 a" y. Q# u
mov edx, 1# H* J/ h; y2 \; V7 |+ t+ `- X3 l8 W
int 80h 7 Z8 Q7 q/ R; n+ ?8 Y8 P W5 W
mov eax, 43 T+ p% m) W( s {' w* h( @/ D
mov ebx, 1- ]; s7 b' n+ Z! R5 h. o
mov ecx, disp2Msg6 f. c; L7 D" y! a- j
mov edx, lenDisp2Msg
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int 80h
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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],0x0a4 C l F2 q2 n' d5 Y' e9 p
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 1 K( K+ H% S. o1 ?0 e1 E
ASC_LOOP:! }' r# S* R) }/ v: h! _4 `
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 . ~: y$ g* z% T5 M/ y; m. V# k* x
dec esi ; store characters in reverse order
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mov [esi],dl: i8 v. m: x1 F/ z8 P
cmp eax,0 7 z9 l, V+ i: a" i
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII' j! R: B, R7 ^) d0 R: y3 P
jmp ASC_LOOP ;ELSE REPEAT$ l: s& w3 O; M' O# `* R+ p+ M
END_ASC:) w8 F% o/ H7 U' P7 ?" |- A
mov eax, 4
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mov ebx, 1
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mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]1 I( I7 t: f6 T, ]2 {
sub edx, ecx0 _4 C$ r: C6 z
int 80h 5 `3 y, z. |& n0 o7 e( G1 x8 ^, k" l
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; Exit code
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EXIT:
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mov eax, 1. m I- H6 W9 @; B
mov ebx, 0
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int 80h
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; Factorial function using recursion0 Z& ?4 G- D: @+ ^$ j0 _
factorial:
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; Check if eax is 0 (base condition)
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cmp eax, 0
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jz end_recursion3 l1 T0 D! D& d- H. m* x$ \
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; Save the current value of eax
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push eax1 [* t# X) Z5 ~1 c- v
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; Decrement eax and call factorial function recursively
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dec eax9 ^. b: W' J# \! B
call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx) b1 j2 m) _% m* M
imul eax, ebx
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ret
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end_recursion:. n) C4 R( s" r, W
; Return 1 when eax is 0 (base condition)
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mov eax, 1
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ret

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