用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
# |! }2 ]& I' l7 l
8 Z! ?% f2 D' T8 u$ D
section .data ;
; z! j+ d/ `& z& t
userMsg db 'Please enter a single-digit number: ' ;) K: `8 ~9 T, H, w9 A
lenUserMsg equ $-userMsg ;
7 ]5 t1 ~# B$ ^/ ^2 x7 `+ R
disp1Msg db 'The factorial of '
6 G5 {5 B5 w; g$ I4 }! i! p
lenDisp1Msg equ $-disp1Msg 1 t0 w( E( a* D1 F! N
disp2Msg db ' is '0 D+ Y# l' j" S' Y/ E3 l
lenDisp2Msg equ $-disp2Msg
1 R) k1 z& n7 D% F- G! w
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
4 a8 `" [+ u* n5 R
lenErrMsg equ $-errMsg 3 N! j& L; D; Z) q. n; j9 O- _
- q' L3 N7 f$ U+ ?- R2 R
section .bss ;2 E8 U9 K Q+ ~
num resb 1
9 W9 I2 @' H' C1 v. b
result resd 1
; y+ [$ E5 j) h: U3 ?: U4 e
buffer resb LEN_OF_OUTPUT+1
! q. o. f H" T
" V6 R, x& J! n: Y8 L
section .text ;7 c3 L' e" ^1 L" A% K9 n: i
global _start
& N/ |1 O) }! r$ I: P
) m; |5 q4 B, c8 D( q! P
_start: ;$ R. H/ Y, c0 W3 }
mov eax, 4! [3 T l6 V1 J k9 e) D+ w
mov ebx, 1
9 }% h& A( \& \% L2 i
mov ecx, userMsg- K! u! ~; M N5 B; B+ b
mov edx, lenUserMsg7 p, r: h7 J6 n F+ ^
int 80h6 x. @) j' g6 j* Y
& z: s4 F& m i4 N
; read user's input
) X' _/ s' l7 y) U6 y" \8 c6 D
mov eax, 35 k0 U" r; b9 x5 g
mov ebx, 0" E* M! v" a5 J& ]$ }2 t
mov ecx, num
3 f7 `! M& G3 q3 M
mov edx, 1 ; length of input buffer4 W5 t# h) r6 G9 ^6 S; U* ~
int 80h
: w" [3 S' V% Y; D
/ m: D/ K, ~& B8 F0 q& ]
mov eax, [num]
* W* U, G) T5 e" S6 N% ^: N4 v# m
and eax, 0xFF( d, c3 L* N; ?5 f4 h9 ]. z' h
sub eax, 0x305 {5 m* l( p3 \: i
jl ERROR
- G. q2 _; k/ V% \( u# W5 c4 L3 r
cmp eax, 10- a6 D6 u e! x* `' I4 X- Q: G' N
jl DO_CALC
3 K$ S. z: ?# {0 X6 C
ERROR:# G, u7 U8 j" g2 y; ?( t$ q- V3 u
mov eax, 44 R. y3 O! U2 f. K. k( J3 T, c
mov ebx, 1" L0 f9 V! o X# q* x# H/ d, b0 n
mov ecx, errMsg% k9 |4 y6 w4 v; \$ m1 b) k- T
mov edx, lenErrMsg% c8 U1 X+ o6 o* p% m) l
int 80h
2 {$ j. }, ?/ v7 B/ ?, ~( h
jmp EXIT( e# T {1 U# g, |* r% K6 d
2 a, s( [- o- d; e- u9 A% f0 n
6 V+ \- e/ d4 M2 Y& U
DO_CALC:# B# j0 F/ F3 R u0 Z) T
call factorial8 u' v# b. d3 X8 A" M
; The parameter is in eax. After calling, the result will be stored in eax., l ?/ k" n2 A R" i! S
mov [result], eax ; Save the result& H& u& k6 V% L3 q- y! @
0 A$ Q% m. q+ ?- q8 ]* ^
; print result/ `, r, s0 P3 k
mov eax, 42 f; N$ X( L4 q4 i1 X+ n
mov ebx, 1
; G! x' H, c3 X3 @ M1 H/ b
mov ecx, disp1Msg
4 X% F8 d o# t H
mov edx, lenDisp1Msg4 D. {6 p$ \$ u ?$ V
int 80h
2 p; p2 L1 l$ c. O k, y0 [
mov eax, 46 C& g' }, P/ Z9 \* Q2 _2 ^- ]
mov ebx, 1# D" u3 k$ ^& P0 f1 z9 b
mov ecx, num
" Z! }$ m- a+ O& x# x
mov edx, 1" F4 W: T5 f M% u2 I+ L) ]
int 80h 5 l* e3 q% U7 k
mov eax, 4
' ]; n5 _! \$ r% f
mov ebx, 1
0 W+ f. o/ Q2 R. F. U" l
mov ecx, disp2Msg0 M1 d$ l) M" d' K# J
mov edx, lenDisp2Msg2 p- d2 c1 I% g( ~) D7 g6 ~7 o1 A7 R
int 80h
. s4 t* b* Y% F: A9 l
$ n0 S$ k w7 W5 G5 I
; output number
( A' S5 _2 C5 }
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
1 p) d5 @3 |4 W* d, G; I
mov byte [buffer+LEN_OF_OUTPUT],0x0a% y' E* @1 o2 D# m+ G4 h& L5 k$ H
lea esi,[buffer+LEN_OF_OUTPUT]
& s: v% A2 P; w' j
mov ebx,10 / o, N% ^" l2 P/ b8 v6 I1 u
ASC_LOOP:
4 X( V2 h' q0 e; D1 D
mov edx,0 ; clear dx prior to dividing edx:eax by bx5 {2 S* ~' d5 |0 ]( k
div ebx ;DIV EAX/10, U g" P* h, w8 W5 K0 \
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER 4 \* h$ S0 n4 {! a; j' S
dec esi ; store characters in reverse order
* ~* [3 N8 J \- P* z
mov [esi],dl' {4 m* i1 v. M3 a8 r
cmp eax,0
5 d0 b- Q0 ~+ W3 ?
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII1 b$ q$ k0 h) O
jmp ASC_LOOP ;ELSE REPEAT
$ B# f! }7 D6 g- k& @* P
END_ASC:
7 k! T, X* }4 {; y% ]" f0 a
mov eax, 4
8 P$ F9 q. p( I# L( x$ k
mov ebx, 1. W4 V2 |, @' X- Q9 w; Y1 y" d
mov ecx, esi1 }+ l% O0 n; w0 s# W! j# K2 F4 l9 A
lea edx,[buffer+LEN_OF_OUTPUT+1]
7 x( z* R! j# Q6 T7 t9 T: g6 O- O
sub edx, ecx* n/ Q& _) h# E, L$ c8 D) g
int 80h 8 ^" z! p( f6 s1 y* p. f
! w) }8 M0 {2 P
; Exit code# g2 p% ~% M: V. I
EXIT:1 V1 d( t# G) ]0 p; ]; g$ v
mov eax, 1, {* z' B; j1 e" v* a6 F
mov ebx, 03 N+ h- G1 J) D: z/ T0 X
int 80h( |& s# I4 m: M) S+ t. M- N
+ a3 e! e1 |/ ]' @
0 h& ~1 @/ d$ S
, _4 ^+ b8 _" [' l
; Factorial function using recursion
% y8 A& I) m/ n5 I+ i: R6 ^
factorial:
4 e( F: l; P+ S9 [' N
; Check if eax is 0 (base condition)
6 A Y1 B- B4 d3 y5 Y2 _5 c# z* n
cmp eax, 0
( b5 d) k( `8 r8 X
jz end_recursion% e6 m+ ]4 k5 [
$ X) n* J. r. x d& v
; Save the current value of eax
: O( g4 Y J8 s2 Q; H
push eax
1 {/ f2 F L1 E9 b3 C
) u7 o5 n1 W! U2 O# |' E, z- S
; Decrement eax and call factorial function recursively
' K7 } R# b- y( q. C! I% x
dec eax
( P) X* ? X+ q- \4 S* O
call factorial! m/ R) q8 R3 v2 C6 o; |
) o; C( p5 A$ I7 @
; Multiply the result returned in eax with the saved value of eax
' Y/ F3 k+ ]6 h$ S; r
pop ebx0 M* _8 Q' S: Z% U% d: D1 ~9 u
imul eax, ebx
6 E) v. B8 }0 v; q% D+ f
* D5 Q: Y) j/ r ?0 }0 N$ L( A
ret
' P& _$ O$ d# b9 }
* I$ w* d+ x# x2 H5 y; G) h8 y- I
end_recursion:
5 [/ E! y7 O4 U6 F! B
; Return 1 when eax is 0 (base condition), L% g3 H7 p5 d* ~8 T
mov eax, 1* J+ X! E O, W9 r" C
ret

复制代码