用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10' B5 ]0 W) a1 k! }* f' q
) D8 N( l' ?1 m( }9 J
section .data ;
3 g7 U) O, t' |. T* C) |* ]: Y
userMsg db 'Please enter a single-digit number: ' ;
7 v3 Q8 J1 y a! [/ R- h/ r
lenUserMsg equ $-userMsg ;, x/ n+ j; t2 i+ M0 `5 |9 R
disp1Msg db 'The factorial of '5 X+ Z5 q) K2 j7 H
lenDisp1Msg equ $-disp1Msg
+ Q( u- h: ?8 D/ y& r0 D2 ~3 V
disp2Msg db ' is '
0 Q$ b! C* M' [+ U7 ]
lenDisp2Msg equ $-disp2Msg
. s; y2 b' M8 h8 M% H$ o, j! j
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
! [) G! G6 S/ |) m8 Z9 `4 c
lenErrMsg equ $-errMsg
' d# S2 p0 K% M; ]
+ |0 j+ N) y$ [- _4 b' t) P
section .bss ;
% ^9 O" {* g+ f
num resb 1
8 H( j5 `* v- {% r! O
result resd 10 C: ~6 B7 z+ m) b+ _" ?
buffer resb LEN_OF_OUTPUT+1 y- p7 w( L9 v( s2 s* w: c; c
9 p! T6 i4 A, C! d
section .text ;. H& W8 _* L% X- W0 v/ c
global _start& I8 @: m2 v z# M3 T' n
2 O; ]+ G2 V# h
_start: ;& f$ m) H% G c* h2 R; X
mov eax, 4
* t( d+ j0 ~) @$ g8 m
mov ebx, 1
* `- Z' [4 M1 L" W5 S! |% I
mov ecx, userMsg
8 i& c8 ^9 i* t, e
mov edx, lenUserMsg; ^# l" C0 J, I0 b) W3 V( E
int 80h( B9 l4 o9 B: F I4 C' M
7 j6 N2 r$ `$ P: t: l+ N3 P
; read user's input! H8 d M+ _5 b/ V& Z# L
mov eax, 3# z0 h1 t) T9 a( G3 d$ f
mov ebx, 0' f: B( [4 d; B/ ^
mov ecx, num
* @" c s% a9 ?2 ~
mov edx, 1 ; length of input buffer
2 o, t, e7 x1 D# n4 i/ r% U
int 80h$ J% T5 p0 \& b2 m1 ^/ g
+ D2 p l1 I8 z$ f8 ~
mov eax, [num]7 R! {8 ^, f4 d' e) S# g
and eax, 0xFF
8 k- N6 s f$ Z* N3 a( M6 J* D
sub eax, 0x30
, w( O f, S$ D7 a# f/ w$ I# @" n: d
jl ERROR; k, [" J+ Z3 p0 W' b1 B- ?! x' a
cmp eax, 10" Z" ^ a5 j. d" `4 H
jl DO_CALC9 C8 R4 X1 R$ |
ERROR:+ Y' ] a+ b) ^; B
mov eax, 4
2 C1 N0 A7 ~9 U4 n+ Q3 ]+ e
mov ebx, 1: l Z1 x/ \( ~: B. g; b
mov ecx, errMsg" D. H; C( {8 R0 P
mov edx, lenErrMsg
+ k# |5 H1 B6 K( k' Z2 ^, h, P J/ V
int 80h % i" v$ J/ |$ M! k. y. e7 S
jmp EXIT# Z, Y3 T8 j6 L( C5 A$ X
! n" Y% `: N! d$ p- J" ]8 r% W
; D! {# [9 K( ?0 _
DO_CALC:
$ g) l) O" m, O0 r( p
call factorial. y8 d/ b3 i. y/ Z0 B2 _7 d" X2 V ~
; The parameter is in eax. After calling, the result will be stored in eax.
* x+ p& [% e8 T4 P/ a. ^9 s1 y
mov [result], eax ; Save the result
/ U8 Q- ]7 Z$ Y/ N, b9 F1 \+ |
1 E* D3 W4 w7 S! L! H
; print result5 q4 t- @0 n2 v$ n4 z
mov eax, 4
! h: t3 i4 {0 {/ p) y& b
mov ebx, 15 C1 N6 p1 o! w: ?
mov ecx, disp1Msg7 l1 d* ~$ N4 d7 _3 |4 X
mov edx, lenDisp1Msg: O: H" R, u) g( Y1 c: C
int 80h % V, e3 }( U4 C( m8 ]6 a
mov eax, 47 C, J9 x4 r, S# _, r6 B
mov ebx, 1
0 O+ b; Y( u* D
mov ecx, num
$ H) z0 I9 e7 E5 G
mov edx, 1" Y" z7 h3 J$ S
int 80h
+ e2 C0 ]8 n' _9 y6 m* R
mov eax, 4
1 ^3 [/ ^' v5 O
mov ebx, 1
2 o' a. u0 k7 M$ J' |6 O$ R9 c
mov ecx, disp2Msg- t" D" m& ?: a; A
mov edx, lenDisp2Msg
1 g9 L2 k- b1 I8 x: a4 i) `1 f& H6 E
int 80h
7 c8 g: t( h2 l1 j2 o
+ O, O% H/ m$ D+ F h* ^; f$ j( A
; output number. B1 C7 q( J1 \8 q Y
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY- d( S$ v% j9 I8 K* G7 R
mov byte [buffer+LEN_OF_OUTPUT],0x0a+ x2 i/ Z. j) x" t
lea esi,[buffer+LEN_OF_OUTPUT]( _0 K5 U; |- ^3 }) Q
mov ebx,10 1 [! L. N8 r1 C, D) U
ASC_LOOP:
! c7 K# h. h0 F( J+ D
mov edx,0 ; clear dx prior to dividing edx:eax by bx
( v% n w" x9 l+ ]! ?8 s
div ebx ;DIV EAX/10
' V- {/ ~6 X* W% h4 K1 q; f
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
% h9 D% k* Y% M: T0 z
dec esi ; store characters in reverse order2 B5 \, j$ P2 P+ a$ R4 W* I
mov [esi],dl" Q( H% N) ?8 d V
cmp eax,0
E$ y' ]& W. q7 [" f3 J
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
) j. |7 d4 P+ _4 Q9 V
jmp ASC_LOOP ;ELSE REPEAT
$ W; d7 o# m' n9 J# C
END_ASC:
* H; K. I% r* {2 F3 p; A
mov eax, 4
7 o/ p* C4 i _. R, ~# o' H
mov ebx, 1
. g3 U" e3 m) b2 Q! c" H# y
mov ecx, esi
' V- s" M; o* ~6 T& ]) x
lea edx,[buffer+LEN_OF_OUTPUT+1]
! ]$ Q: `4 X" Q' |' C
sub edx, ecx7 j5 N" V2 B# J+ W5 f( ?; H
int 80h
# m8 X, d4 `" E$ W' U- [; z+ B
7 f% I5 x0 }7 ?- h) ]/ w u) ^7 {1 Y
; Exit code
- r% C$ i- j# Q: G
EXIT:9 i6 H8 p4 n+ d; m( k/ @
mov eax, 1
Z$ G# Y7 r% V' @2 ?
mov ebx, 0
6 x' A- m; K, Y
int 80h
9 J5 z. I! F: f% d
+ n; a6 Y. M0 s2 n# `8 ]
s2 a6 ]. L/ @/ P8 s0 W2 d8 P+ A
7 X5 c- ~0 k: J% g" g! r; f1 p) I
; Factorial function using recursion
- M, [% G" h$ A8 ]) v2 k
factorial:
: P& S8 W0 a h% p
; Check if eax is 0 (base condition)
1 W/ ^9 q6 i/ t8 f
cmp eax, 0! c! X1 A9 n1 ?- O5 K! j# Y( q
jz end_recursion
* w. e0 W! h) F
) @1 z M# T/ t5 U/ F
; Save the current value of eax, Z/ e* |7 L& Q+ D* L& }; g
push eax# g% z! m& R, Y
( h& C A: I$ l2 h/ }4 t6 T+ \
; Decrement eax and call factorial function recursively1 { H( [: b1 h
dec eax
9 `" o: `6 A& O
call factorial
+ \9 H: K5 t; R' `* W% n
+ ]& P2 C, ^- j- y* \
; Multiply the result returned in eax with the saved value of eax
1 b, O; t7 w5 s3 P1 t! l
pop ebx
& o7 a5 ^+ I/ C' A' T- K. W' W4 |
imul eax, ebx- T' p9 Z# k; X( V% s& j
& ]% z4 M. q Z F3 O j
ret$ |" t! o9 d n |7 P
# C, z* h7 _8 t$ h9 C7 _
end_recursion:
3 Z* G+ C }( l* I
; Return 1 when eax is 0 (base condition)
; T! j8 e; x8 h
mov eax, 1
4 ?% B5 O7 h5 R v7 I& {. a* }2 Z
ret

复制代码