用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10& M, S: o9 ~& W u/ ~# ` Y
" W1 g+ n" L/ Z+ S$ k' u; a
section .data ;
7 d- f) _9 l7 J$ d" u: l
userMsg db 'Please enter a single-digit number: ' ; M" q- f$ X3 [ C$ E. K7 p- O; N, n
lenUserMsg equ $-userMsg ;: q- V: M9 J- K/ K5 d
disp1Msg db 'The factorial of '
, |$ q' P$ d' m2 F3 }
lenDisp1Msg equ $-disp1Msg
$ ~7 `7 p) G7 f: U+ ~7 \$ P( A2 z
disp2Msg db ' is '
1 W/ O( x0 ~/ q3 o; Z' Y
lenDisp2Msg equ $-disp2Msg
2 U r* T! F9 c- D) k8 T9 V
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a! j- U2 I" q. J- w8 [: \+ [
lenErrMsg equ $-errMsg
( P7 R3 L: ^, n3 ? B
3 W9 A8 W# t% w. C; S6 [' V( G
section .bss ;0 I6 Z7 @. |6 [% i' a/ l1 J
num resb 1
) E, R: e2 D$ s, n' {5 J
result resd 15 n/ H' X( I: {- B3 X% Y
buffer resb LEN_OF_OUTPUT+1
5 V9 [6 g9 P& z; L4 l
1 B' d9 t! r( C( x: L3 u7 X
section .text ;9 K! ]* s$ ~! F$ T! Y ?2 i7 |
global _start
8 G, N) Y: S$ M" A
# Z% o: v! Y% u/ N+ Z
_start: ;
& \; q3 q" E, B" t& f4 z2 D# N
mov eax, 48 I# Z. ?% u! h2 E m5 o2 ^
mov ebx, 1
+ |- c) Q9 m' m
mov ecx, userMsg2 [% O7 ]( E# T. z: _$ c
mov edx, lenUserMsg1 {' @% ]0 J' }: x+ k# P/ [* k
int 80h
1 L3 \, K* z6 e3 s6 K* b$ P1 F; i
/ |: F3 D! d* g$ V
; read user's input& I; h" Q1 P" D
mov eax, 3
, [" X) W8 u* z+ c# `" ~% L+ s9 J
mov ebx, 0
0 W+ |; j# D- A: }9 K4 @
mov ecx, num ( t, w5 h* U/ S. E: {$ m
mov edx, 1 ; length of input buffer# D7 X; ]9 ~9 n7 |# {: @
int 80h* o3 X; O( j8 V3 i b
# R/ g1 C) [: {: F; ?1 [
mov eax, [num]- }- M2 ~0 m: @1 o1 ?* m) \" G, m
and eax, 0xFF" y0 ?0 Z5 r, {8 p
sub eax, 0x30
% Z1 `: J4 n- ^4 Q% f
jl ERROR
$ y6 F0 a: t; p8 A9 L3 x
cmp eax, 10
* m% s' G! v' y; I) b2 q* t) u
jl DO_CALC
4 c, B; Y- u, N9 N( s- x4 I
ERROR:
/ A# x& E f: ]; U( y9 K" _
mov eax, 4
+ d9 w1 |, B; A6 q6 g+ t, z: v6 f
mov ebx, 1
' a) Z. F# V: X) e" p
mov ecx, errMsg
+ u6 ]) l7 d' E6 Z. l
mov edx, lenErrMsg
0 I7 {. K2 S8 m- y# w2 q9 {' g. Y& h
int 80h
' s/ f$ W& r& M! H v. M& T
jmp EXIT
" N( `4 w0 N/ y& D8 ?+ ^# |
4 {% t# N i. ]& H+ S6 D3 F6 L; ~ V
+ x6 V& Z( Y. c& f4 V+ C
DO_CALC:2 N l% n, [/ Z" d
call factorial3 t* G* g) C" z5 S8 k
; The parameter is in eax. After calling, the result will be stored in eax.
! r- q& g2 I. E( N: h2 F1 _
mov [result], eax ; Save the result4 l8 u8 R; b! A
+ c2 T3 }: x: f4 O, s7 d
; print result
mov eax, 46 W6 y! j b; g
mov ebx, 1 q: W# }- D- d8 {1 x
mov ecx, disp1Msg; I! U, ~. G; P
mov edx, lenDisp1Msg' h( K1 `, \. U, `7 K$ [! R
int 80h
7 D3 C9 \. p ~3 M, e* v
mov eax, 4
8 }* l- c+ ?1 h3 v& X$ i& c# b
mov ebx, 1
3 T' C. D J: m
mov ecx, num
' H' z0 W) o& @7 h/ U
mov edx, 14 [1 i# y4 P4 s( [" [' X. {3 \
int 80h
& I8 W j5 F( F; p
mov eax, 4! ~5 i5 u! x5 @' {# c/ D* H5 k$ h
mov ebx, 1
( d* h( E' c: M4 W. G
mov ecx, disp2Msg3 ]0 x w# x2 n s6 h# d
mov edx, lenDisp2Msg
, ^5 ]. H; t O; ^
int 80h
6 Z. ~+ Q4 f0 F1 C; t
0 S6 x4 y. u( L3 h4 Y% o2 T9 B
; output number: `/ h5 m# l6 w4 n: g+ b9 u' b5 s
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY9 s+ t" U7 P' d0 P5 T
mov byte [buffer+LEN_OF_OUTPUT],0x0a
6 ?, B' B' b2 @. W% { \5 J
lea esi,[buffer+LEN_OF_OUTPUT]9 n/ u% {' @1 j4 O# ]
mov ebx,10 ; p7 d, \8 Y1 q0 ~! r$ A
ASC_LOOP:! h" R0 d# d9 h; }: U) J
mov edx,0 ; clear dx prior to dividing edx:eax by bx+ `# i4 g) x, ]
div ebx ;DIV EAX/10$ J$ f- m& i" S1 M4 m+ Z# v
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
, n4 c/ z, x0 d( ?1 m# M
dec esi ; store characters in reverse order& _" G) u* K4 e; G8 ^* e
mov [esi],dl
0 M, A3 F+ V: u+ X5 f9 H, |% ]
cmp eax,0
8 F" e5 F; j5 E2 [( G
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII5 R9 I% k! c2 A
jmp ASC_LOOP ;ELSE REPEAT* O' \) H" l% b% n& G5 u* [
END_ASC:
& _: ^* s( R8 F
mov eax, 4
4 `! ]2 e: B" p+ j# ~: @2 ?
mov ebx, 1
8 q4 |9 G. v% u' P0 z5 b" A, e
mov ecx, esi1 b2 C5 s7 Q1 ?# Q$ a: Q3 \1 f
lea edx,[buffer+LEN_OF_OUTPUT+1]
2 O4 C! t v0 D. h7 k
sub edx, ecx$ Z$ d: U5 m' a5 Z+ `8 V$ r& o1 _7 g
int 80h
, F7 y0 E, u1 `" w3 R( m
* G: S1 y; G Y1 J1 d3 C/ x
; Exit code
6 {# d* z' h0 e- {; O1 W
EXIT:1 z% I: B( \ _$ H; M4 H
mov eax, 1
: o& P& Y6 U7 P$ d+ y
mov ebx, 0
# U/ T# |0 o* [' `6 C$ v1 C5 m
int 80h; N8 ~6 j' L/ C* W* C T4 m5 M
: E$ W/ X+ K7 E& R( l( P
% l @8 b% X8 M) A" N
$ }+ o5 `6 H8 _ a# @/ h
; Factorial function using recursion
: R8 G7 G# b0 F6 X; p3 u' G+ C
factorial:% j# y1 l) u0 y/ }. A
; Check if eax is 0 (base condition)
2 |. V' i! ~+ w r5 V3 a& D
cmp eax, 0. y$ g, A" ?; G ~! V/ m
jz end_recursion7 @- f5 ]# q& F2 b1 Z
- t" z9 e2 ~' i, |6 C- ]
; Save the current value of eax# v, B7 u) s; f) V3 l* b) c0 F
push eax
6 d/ _7 i/ N( L
. Y8 P3 ?# H6 Z' E% m w
; Decrement eax and call factorial function recursively
# a% h: m* ?* j/ _* Z' ~
dec eax& P4 F' h" W G
call factorial
1 q C ]1 M+ l+ m6 P
`1 z* }$ x0 \) d$ E+ F" I, K
; Multiply the result returned in eax with the saved value of eax# e) U2 K2 r! R! J' o# Z, S) ~7 s
pop ebx* O# T+ i2 e; |0 O1 d! e- |
imul eax, ebx% ?% |: W0 V9 V" X. d
! H3 H) H# D3 C- d1 w
ret& c6 }# F9 ^& p; I
( \, Y: y/ f" t) n0 J% z) m
end_recursion:& {( J- X( D4 h( V; `) F4 Z, m
; Return 1 when eax is 0 (base condition). K3 p8 p) F, F1 }3 ~9 q
mov eax, 1
% ^# _2 C4 h5 q3 ~6 T
ret

复制代码