用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;+ H3 m# I2 X5 j1 X& L
userMsg db 'Please enter a single-digit number: ' ;& J- D4 ^# E, a0 I
lenUserMsg equ $-userMsg ;
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disp1Msg db 'The factorial of '% d6 |& e/ _$ b8 o B5 S
lenDisp1Msg equ $-disp1Msg H8 O. z1 q, {: w' b# H8 X; F
disp2Msg db ' is ', t7 ]' a: l6 B$ R1 M. a! k- T
lenDisp2Msg equ $-disp2Msg
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errMsg db 'Wrong input. Only one-digit number can be accepted.',0x0a
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lenErrMsg equ $-errMsg Z4 K4 { _% `6 d: Q
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section .bss ;- N9 w2 q, N) F9 Y( h
num resb 16 D+ i6 v* [- e) H. I' v8 ] c* g4 [6 q
result resd 1* h% w2 P3 A$ [( X1 m2 b
buffer resb LEN_OF_OUTPUT+1' K4 l) H! _5 u! E& s: U2 o
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section .text ;* s1 @( ?8 V( d0 G, O, Z: }
global _start8 ^3 i& c( k! L- m
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_start: ;' a+ b) {% d7 c5 c4 j& U. Z3 K
mov eax, 4
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mov ebx, 1
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mov ecx, userMsg# a$ P0 k# _$ V, j2 o; \
mov edx, lenUserMsg$ _1 f( I) z, Q
int 80h7 X) d/ B$ z' P. S) w
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; read user's input
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mov eax, 36 _/ v; W3 I: k, h; ~; \9 O
mov ebx, 0$ N# r( M' c1 _% p2 ?4 b
mov ecx, num
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mov edx, 1 ; length of input buffer7 X3 d: P S3 Z8 X. b6 G6 ~
int 80h
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mov eax, [num]
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and eax, 0xFF9 c6 X3 {$ o7 k0 z! z& Q, |. x2 f6 |3 [
sub eax, 0x30
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jl ERROR
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cmp eax, 10* d; P/ R8 O/ ?5 ?
jl DO_CALC2 v9 P) m+ @! i4 D5 {: d+ }: s: |
ERROR:; ]5 ]. h' ~6 N o4 E7 g( V" @- }: G$ ]
mov eax, 43 ^3 k* t1 _7 r4 W
mov ebx, 11 h7 J( a, I7 v' c
mov ecx, errMsg4 c a7 i; c+ E/ R% N9 d0 b
mov edx, lenErrMsg( V! a8 k" Z7 h: Q" ~4 z
int 80h
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jmp EXIT
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DO_CALC:$ }1 r0 ^; y4 Q4 G# c: e
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.: y9 ?' Z% [. E
mov [result], eax ; Save the result! K( I" J% `: U$ m1 o9 m, I
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; print result# Q2 i2 ~3 O3 H0 ~
mov eax, 4
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mov ebx, 1
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mov ecx, disp1Msg& B9 j! |$ s; Y9 c
mov edx, lenDisp1Msg% n4 |! ` S. r6 Z1 ]: n
int 80h % i0 ]: r1 s, I# @$ U
mov eax, 4; r. H$ F& U4 J2 u7 ?$ C% |
mov ebx, 1
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mov ecx, num
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mov edx, 1- y# z9 R4 Y1 K1 \; c# L
int 80h
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mov eax, 4
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mov ebx, 1
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mov ecx, disp2Msg% z3 ?- x4 J* f9 Q
mov edx, lenDisp2Msg
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int 80h 1 R! n8 o& r) G d1 U
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY' _: s! T( P; M
mov byte [buffer+LEN_OF_OUTPUT],0x0a4 ?! `! ~" n; G, r4 b ~2 m4 q8 \
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 7 b" S8 e# A: P6 I% ^9 E
ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx& L; G4 w4 ~! ]/ d) e! n+ V
div ebx ;DIV EAX/10& X9 F7 h; G3 a7 D. U- R9 A* j1 D
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER ]" `/ \, R7 i
dec esi ; store characters in reverse order9 M; @1 x0 N" V+ a3 R E; \
mov [esi],dl
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cmp eax,0
; \' i+ u1 r* B/ g
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII
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jmp ASC_LOOP ;ELSE REPEAT1 `2 \, G8 [5 y) `* U8 ?
END_ASC:5 A# I* M5 {. i* C
mov eax, 4/ f {+ T; S0 z% J$ P
mov ebx, 1: v6 |" f1 a- h# u* R" ]: R
mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]
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sub edx, ecx9 |2 ]7 {! `/ I4 U; {# }: _
int 80h
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; Exit code
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EXIT:
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mov eax, 1. d& V$ g* E" ]1 G- l2 H2 r
mov ebx, 0
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int 80h7 l& Y( l) h3 [2 K0 U% c
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; Factorial function using recursion$ `/ v/ x8 \' @* ]
factorial:3 D3 E3 \# U4 C* L7 i! m' u! Z/ D
; Check if eax is 0 (base condition)# R* F8 b" D6 J6 e" m" O/ y/ V
cmp eax, 0
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jz end_recursion( b& p% v; e& F( {4 [. r
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; Save the current value of eax. m- k1 w+ s& J( e9 A
push eax1 h$ u7 Q; Q8 U
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; Decrement eax and call factorial function recursively: i% Z- r9 Z5 X1 F9 H% X u) p2 k
dec eax
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call factorial
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; Multiply the result returned in eax with the saved value of eax
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pop ebx
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imul eax, ebx
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ret
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end_recursion:
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; Return 1 when eax is 0 (base condition). L* ~" n: D$ I& R+ s( Z
mov eax, 17 r- p* |# @3 m# o& y
ret

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