用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
; V3 c9 Q6 Q" u& K6 \
6 i y0 I/ f u3 [6 e
section .data ;7 o* z+ G) h; m p5 }# V* ?9 Q- m
userMsg db 'Please enter a single-digit number: ' ;( z# u+ x. k$ F: N- v
lenUserMsg equ $-userMsg ;% u- B9 K$ o# \6 t" j( ^
disp1Msg db 'The factorial of '* I u/ o$ {% o1 y, S
lenDisp1Msg equ $-disp1Msg
! k. {4 W5 A% a& P
disp2Msg db ' is '9 ^- r4 ?! t2 U, ~) F
lenDisp2Msg equ $-disp2Msg
x$ g2 N$ i* X- G- ]$ Z
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a) E! f6 w( d6 l! n, V
lenErrMsg equ $-errMsg $ ?1 i3 U9 c: ]1 D* K9 |, Y
9 q4 j# ^8 O( D4 J3 j
section .bss ;
, i% D5 D. b5 F! [
num resb 1
1 Y; J( u; p- o9 C' ^
result resd 16 i, u$ C; @3 ^) y
buffer resb LEN_OF_OUTPUT+1! x- e$ K' x5 n$ `
5 W/ T* K- G4 ]8 P
section .text ;2 p& H) {- Y) T/ N+ f# ^! i
global _start
8 I* d( D/ I$ f# r0 w
" Y/ R# n& w9 ]* Y9 ]8 `$ l. m# s
_start: ;1 v( r M$ P7 U& }- v4 L( {
mov eax, 43 K& x9 R' P( M5 `
mov ebx, 1
& S2 B. p/ h1 f& k: F; L- N8 }$ a( [
mov ecx, userMsg
# a9 F8 {7 \8 h! ?
mov edx, lenUserMsg
: u6 @! N0 P2 T; [; { L
int 80h; ^+ @0 X+ w8 u3 ]0 ~
5 A( r/ d, A' ]1 C) D7 z" D
; read user's input8 c- n$ L! J1 y
mov eax, 3
0 J2 o- M/ L7 o" |/ }+ E$ e
mov ebx, 0
+ M% o* Z3 }- |
mov ecx, num
+ i) }3 a( l L; ~- ~8 p
mov edx, 1 ; length of input buffer
- t, b* u) Q) Q( @
int 80h7 a r: a: s0 n
% P: C" g- j& `8 `: t, e
mov eax, [num]
8 u* ?0 A9 P$ s: q) k! I
and eax, 0xFF9 d _) S5 ^5 }5 b! ~
sub eax, 0x30) Z) W; [" _2 _# L; o: z
jl ERROR
$ [3 q! M/ x1 O r0 t
cmp eax, 10& v3 s. O8 X$ n6 l! }3 ]$ a
jl DO_CALC
' U3 S/ r0 F9 [. u* e9 k$ }
ERROR:
' M- ]" `: x' h1 u8 w, ~# k
mov eax, 4' A' E( v' `" Z; Q5 x
mov ebx, 1
! x" ~) z2 R& v- b. R7 k
mov ecx, errMsg
! K: r% z. a4 v* q5 {3 D( O
mov edx, lenErrMsg
. |1 p' h; ?# h" e" D6 i
int 80h 4 [8 o' X8 w0 H, T4 C9 V- r7 j {
jmp EXIT0 G, y8 b) s- A
6 x7 D( a7 M7 Q0 a/ b
7 A" {) }& b$ ]- @$ j% x/ K
DO_CALC:% Q! m% Z+ [) ~( _5 j, X
call factorial
5 L6 c+ C% v1 O ]
; The parameter is in eax. After calling, the result will be stored in eax.
* N; V+ e& A5 \( U
mov [result], eax ; Save the result6 g3 b7 n% L& c4 |# h! S
. u, N% j) n6 v0 D
; print result
+ F5 E# s) d v) |' U* ]. `
mov eax, 4
6 k7 R8 a9 p: x& k& g& V5 x
mov ebx, 1# G4 E6 Y% R' i$ }8 Y. L
mov ecx, disp1Msg
6 ~) ?% g$ K( s3 n1 D9 I/ C
mov edx, lenDisp1Msg
" I" Q- C, g4 Y' j* t$ J0 Q
int 80h
/ I9 [; a9 x* {; I% d4 g! A- ~
mov eax, 4
. N! D$ ~6 r( H8 K
mov ebx, 1' R$ N# {7 L6 S9 w
mov ecx, num
+ s4 @! p: D$ x7 v
mov edx, 1/ m" X; g/ v- ^! E! A; z2 U# W. [
int 80h
; u6 O* i, j2 ~% {. ` v
mov eax, 4
5 s: C' u* A1 A& H
mov ebx, 18 e3 N/ P/ X1 [9 b3 D
mov ecx, disp2Msg+ D) F. O' D% C% G: T! l7 w
mov edx, lenDisp2Msg
5 Q1 h, w% k4 g4 E' X
int 80h 5 E, h O' t3 ^# `( Y
0 F+ g! f2 E$ W9 _2 I" [
; output number
; ?9 p7 H# W/ P1 f, H+ s
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
, f! E7 m* L. m. k' E
mov byte [buffer+LEN_OF_OUTPUT],0x0a
1 T- ]; r6 a* U! i4 j. z8 U2 ^
lea esi,[buffer+LEN_OF_OUTPUT]) q1 g, b& Z G3 X4 S: |$ }/ ?
mov ebx,10 & U; h: [: \2 z: m5 ~
ASC_LOOP:- t" W, Z. s w' {
mov edx,0 ; clear dx prior to dividing edx:eax by bx; |8 z. o) o6 u2 E6 ~/ i
div ebx ;DIV EAX/106 g: {% M+ p! y6 d
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
# O5 a! r7 M# F9 M e+ Q* F9 u
dec esi ; store characters in reverse order
9 q2 N) h- [& I
mov [esi],dl) W" o2 a& A( J! c" ]0 e- A
cmp eax,0
5 m ~8 u4 k! G* |& k% t
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
6 r ?) i0 V7 `$ n+ f
jmp ASC_LOOP ;ELSE REPEAT
3 t* y+ X6 [1 h$ L/ b% o C
END_ASC:
$ A5 j; b6 `6 |& b/ A
mov eax, 4
, C$ P& j% C: h) t
mov ebx, 1
; i; Z& S; o: \, F6 Z$ B
mov ecx, esi
+ G: g# H6 g' p" f; Y, y
lea edx,[buffer+LEN_OF_OUTPUT+1]" q% [$ C3 ]& V
sub edx, ecx3 b/ Y, H: ^8 N8 N3 e5 _$ N
int 80h ) } k, A# H9 H; m Y& f
" S9 P) P/ L. z4 }0 e
; Exit code
* U6 Q" ?( t: o+ y: ^; r. t
EXIT:, t0 `/ f; _& }$ Z0 F3 I
mov eax, 1, n6 F8 h7 J" ~
mov ebx, 0
8 h: }* I+ o! s) N# C1 o3 v
int 80h
% v |( y) G4 t
* d% g$ }9 k/ M( O$ D9 M! v+ {
) t9 O" z" a: t- Z
: x) U l! o/ b R
; Factorial function using recursion/ Q) a; t( J: X/ p
factorial:# \9 k" l& z; W/ e# W
; Check if eax is 0 (base condition)
+ t% y0 k( P, I( l( S
cmp eax, 0' @" P1 K( l0 |( I
jz end_recursion7 s, ^: q# i3 I0 x
# V" D6 K* X B& q' S3 u
; Save the current value of eax
6 A0 `9 {3 B( M* q) \3 r
push eax
4 e- z- Y9 Q3 w' }
& E# @9 r' E& v0 t0 x& [6 _3 r. l
; Decrement eax and call factorial function recursively) C& p' t1 \4 J. x8 T0 F
dec eax
7 X( c" k* Q+ U& H7 M
call factorial" f R" o' b- ?, ~
# x+ j- u* S. t& B; N
; Multiply the result returned in eax with the saved value of eax
: O3 c, p; k* ~
pop ebx5 U. S) u% [% W. a+ d7 S7 H
imul eax, ebx" z8 K: z$ i" f
5 R$ w$ B e) U# T
ret* g/ M" h0 o$ f3 i
% s, D* ~$ T Q/ l l4 {. }2 y7 q
end_recursion:/ O8 y4 i0 o5 L/ U* Z
; Return 1 when eax is 0 (base condition)
v# g% A# C' \9 P7 q5 ]
mov eax, 13 o3 |, Z9 D6 l& m4 B" k
ret

复制代码

nasm -f elf factorial.asm
% ], c9 q- E$ y
ld -m elf_i386 -s -o factorial factorial.o
0 R7 v1 |3 d8 ] c" N1 S' U
./factorial7 Z5 |% r9 Q& X; Z9 a+ e! \

复制代码

; Factorial function using recursion
2 i) p( A @+ f1 Y) ]- ~
factorial:& K/ }. G4 Q7 v
; Check if eax is 0 (base condition)! R" ~' d2 s" i9 s M0 |9 o( e
cmp eax, 01 k5 B2 z( L0 g( ~/ e6 i. h
jz end_recursion
8 c( N2 A4 R3 p9 Z- s' L
+ H' _! m' q' l5 U
; Save the current value of eax P. l! l3 |! `) I0 ]. A4 m
push eax( M& @! O3 A- W* E A
' W0 ~' Y$ x7 x$ ]" ?" f* {2 ~% u; @' G
; Decrement eax and call factorial function recursively/ W3 |2 P4 r0 W& x
dec eax
5 Z# u6 ?/ g$ w
call factorial
3 `1 a$ ]' _5 Y, F4 m# o
. t3 l/ I' z+ O2 g
; Multiply the result returned in eax with the saved value of eax
' |9 O! k8 L1 ] a3 Q- d9 q+ w# V
pop ebx* `, }( O: O7 p9 h% k: X9 ]" c4 ?
imul eax, ebx
4 e7 j9 y' d3 O+ b- M, }0 S- t3 @' }" ]
; o5 q J8 J% s! p1 y0 Z* G1 l
ret
1 [# `' v: S$ Z# f6 R
- D+ g; v4 ~" s8 b0 @ r
end_recursion:
: Z6 A$ D e7 ]- C" w3 a! K
; Return 1 when eax is 0 (base condition)( @" v& ~+ @( @
mov eax, 1/ A$ h# E' ~# s ?8 ~( C
ret

复制代码