用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
" p, R. O! M, c3 P! ]
/ j/ m" a% i- N# G3 ^
section .data ;
% S5 i* J. k8 T1 L
userMsg db 'Please enter a single-digit number: ' ;! c' k6 B1 ^# J, o# m" i& Y
lenUserMsg equ $-userMsg ;
1 D6 d6 i3 O7 m; U
disp1Msg db 'The factorial of '
! F {& y& @* l: s
lenDisp1Msg equ $-disp1Msg
c5 D0 s* k2 b/ W
disp2Msg db ' is '; ?6 _8 ~5 @ A+ U( [# m
lenDisp2Msg equ $-disp2Msg
2 N# i4 S/ G) f5 @& v( [
errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a, p: q4 v6 {/ X1 j# {$ C( N6 Q6 \# i
lenErrMsg equ $-errMsg , j5 Z) r& H1 i$ I" t8 |9 D$ r
2 Z# |4 q/ t/ b& {
section .bss ;
, E' _. A, Y8 _/ } z
num resb 1' i4 X% y) d8 [$ I @) \8 j
result resd 1
1 d. { F4 n. G3 I: E& X, \! D
buffer resb LEN_OF_OUTPUT+1* p" b* f# ?5 j# x7 \9 y
' W1 E* ~ ` u# R, Q |7 ]! u# j
section .text ;( v/ e1 G1 A6 ~0 `! Q5 Z
global _start
( e. p/ |/ @; g: x- P& {- W2 W
' M9 w; Z+ l! P8 C9 {$ G% O" q
_start: ;
, `# o5 O4 h p6 B2 Q/ S
mov eax, 4
/ l; H: K7 f" f( \; u+ w
mov ebx, 1
8 ^2 e6 G. c/ F& I: n+ B& [: i, s
mov ecx, userMsg
7 @* ]- H4 F5 g, J, z3 F
mov edx, lenUserMsg
( D- k- Y, R+ E. Y
int 80h# y/ v$ z' A0 p" g. q4 |
7 s! K! _" }; `3 R& }; ]) L
; read user's input( d4 |7 p( ]+ M3 l8 T7 u- j
mov eax, 34 A6 |% |4 \ Y- N# y; Q# h
mov ebx, 06 q( V! o$ X2 l* ^" C3 I! m
mov ecx, num d8 T) k- M% u5 G
mov edx, 1 ; length of input buffer
/ ]8 d, {4 B# V& Z. |
int 80h. p6 v3 @) [. v9 Q1 Y& i, w% \$ N* l2 `
5 N2 ?0 I; y l* A* A: T
mov eax, [num]
- ] p. O4 m4 G' P" B7 I
and eax, 0xFF
, O% W J. Y9 s$ I6 A
sub eax, 0x30
1 ]( ]+ ~' V( I" a3 D
jl ERROR- Z: _4 |' d% H% ^
cmp eax, 10* `. ^3 D1 Y4 B5 ]: O
jl DO_CALC
( K! u$ p% N, ^ S4 Y
ERROR:
# x7 C1 e q( f/ W/ X/ w9 q
mov eax, 4
/ i( l8 F9 D8 i W( r) f
mov ebx, 1
6 v M7 c$ t% K
mov ecx, errMsg
. [/ q2 ~1 b$ r M; q f- g N
mov edx, lenErrMsg S0 o; @& f, r2 v
int 80h
$ {) f/ I8 }9 [
jmp EXIT
+ I( r. |' y5 M
: d+ y- {' k2 g0 K o+ }
4 }8 P6 [. W5 z/ z' Z5 M3 ] l+ I
DO_CALC:! J% d) f* g5 w+ R' A( Z
call factorial
! j0 [5 z$ |* h
; The parameter is in eax. After calling, the result will be stored in eax.& e4 z% S7 n6 v# x' P+ e& F
mov [result], eax ; Save the result
- S9 F: [4 i& x. U5 c1 R) s, {
0 y4 T* X/ ~# M; [( U) B3 ? |
; print result
* B Z5 f" k) C; a i
mov eax, 4
0 i8 U4 Z+ N1 m3 ]' \! B
mov ebx, 1) r4 J- b- v. ]' B* R* ]8 c
mov ecx, disp1Msg
) D+ f, d7 I! b7 A+ d& i
mov edx, lenDisp1Msg
7 O8 v" d4 X& U! i/ ], g
int 80h
1 j- e, g* R$ Y6 |$ h
mov eax, 4
/ b, i5 F/ Y I1 }1 V+ V
mov ebx, 10 Y% A# k! H7 c1 ^' ~7 \. p) j- S
mov ecx, num
( \" O% {) B* B6 |( E. c
mov edx, 1
! o0 d# V8 k/ {! W
int 80h " H% H* ?/ n, m; m4 R( \* Z
mov eax, 42 [# |* ~. R9 G
mov ebx, 1" {4 w; f) B+ i
mov ecx, disp2Msg; f" R3 I8 P2 A# K5 D8 T
mov edx, lenDisp2Msg
# ?, l3 [4 j. i( F/ E, g& O% Y
int 80h
( q; {& m/ d% e8 V: G
, J- |: s9 X2 o6 p$ s' I- S% _
; output number
, E8 M' ]0 c, h. p& n
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY- [! l6 i0 v. F/ v: L8 ]+ X
mov byte [buffer+LEN_OF_OUTPUT],0x0a5 a) I& |" q9 d, }$ f
lea esi,[buffer+LEN_OF_OUTPUT]
( b/ Y; E$ t- V; T6 A8 W
mov ebx,10 3 [% a5 B: n6 X* a& o4 o
ASC_LOOP:2 W) T7 p4 T1 L) k0 u
mov edx,0 ; clear dx prior to dividing edx:eax by bx0 F7 x( U! c, K5 {
div ebx ;DIV EAX/10
* p' @0 j2 b+ R) ?
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
$ q* E7 `# R0 M6 [: f( \/ N, y
dec esi ; store characters in reverse order7 J' W8 o* h9 n- c7 b8 G/ V: f+ l/ C
mov [esi],dl% z$ L) [9 }8 q# U6 p
cmp eax,0
- o2 i/ `" V4 y- M; B1 c
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
- l. K1 M, ?. o
jmp ASC_LOOP ;ELSE REPEAT7 B% ~; u$ \/ l" M3 p
END_ASC:: y) d# J7 x4 H+ \5 |
mov eax, 4
2 r: O; I" Q5 B/ p( P& S
mov ebx, 1
4 s% {9 _3 ]! `9 o! d: c
mov ecx, esi
4 e H1 ? }6 b3 E
lea edx,[buffer+LEN_OF_OUTPUT+1]
w! v/ y, H- a2 R: {" q
sub edx, ecx
# U6 y1 y- O, b0 Z; a
int 80h 6 r: g8 _ w7 c- z' I6 S
( L' X5 i4 b: b! E1 W9 { p8 |
; Exit code, ]8 Q7 G" f& K2 ] z1 ?
EXIT:* ^& x% u* k3 z
mov eax, 1: o5 i: v% o3 b) F# o5 q
mov ebx, 08 q! ~" A o6 ^) x
int 80h
( y' Y7 V4 ~+ \2 x) ?% m
7 F* z! ~" B9 H0 H& e
) v6 Y9 M! T7 o) `% @* k4 x$ _9 q
1 K; e, [6 L1 [4 ~
; Factorial function using recursion
, |8 \ L7 O$ w: H* L
factorial:
. Y( [. I' i$ q7 K! s0 v, \
; Check if eax is 0 (base condition)3 \# [) ]! K5 h! E
cmp eax, 0* R4 b/ p0 c- @( m/ }- X
jz end_recursion
4 R; G: D5 D) t* f" I
- n; ~" D$ K+ m
; Save the current value of eax4 k1 F2 B% ], Q d' W& b3 u7 x
push eax
# {& v. d, h' b i
( Q2 j5 K3 J. o9 o4 m- [
; Decrement eax and call factorial function recursively
; G) I2 \1 |5 _
dec eax$ c6 [; h W5 x8 d
call factorial, b# ~3 [4 n) X
- R/ x; X1 `8 `( q7 K2 k) ]9 W5 f! U
; Multiply the result returned in eax with the saved value of eax5 M+ |0 D- e# c6 v' u' [( l9 Q$ j% Y
pop ebx
, L' u3 ^4 a3 f& X/ x/ F# E
imul eax, ebx
& Z) I5 T# o: u" ~" B ?8 A! D6 f
7 A2 i+ b0 n/ E5 I8 Z$ l
ret9 I; z0 I8 g& ?8 A( Z% n x
& s* N) f- G& P4 h
end_recursion:9 S9 z! P* e! Q/ A2 f6 k! d; {
; Return 1 when eax is 0 (base condition)9 M* L% p1 e& s8 K$ |8 S& m$ F3 b
mov eax, 1
7 U. c8 s9 C9 ]0 i
ret

复制代码