用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 10
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section .data ;% c0 ~% o- C: r0 j4 f6 U
userMsg db 'Please enter a single-digit number: ' ;; L; j- _& m M
lenUserMsg equ $-userMsg ;$ }2 e- }( @7 n
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg 2 r7 ]" D6 j8 t' F2 }* Q
disp2Msg db ' is '$ B5 V& [+ C2 o/ B( {, d
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 $-errMsg * S/ N, \" A9 y! a% ?4 u- O3 g
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section .bss ; d. w! P( ?$ m6 w: U
num resb 1
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result resd 1# q- D* }! N5 g5 w. e7 O
buffer resb LEN_OF_OUTPUT+1
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section .text ;
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global _start
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_start: ;
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mov eax, 48 a+ C7 n* M1 C2 j; B4 y
mov ebx, 19 e2 s' x. i+ f1 z+ M
mov ecx, userMsg
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mov edx, lenUserMsg* Z' x0 Q F1 n2 S3 \9 t
int 80h
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; read user's input% n! B5 @+ M x6 j$ R7 `3 ?4 p0 P
mov eax, 3
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mov ebx, 05 t5 ^ M4 c* n9 M5 }
mov ecx, num * F2 T' W. V0 |/ u1 C* k
mov edx, 1 ; length of input buffer
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int 80h. u) C: I( t: T7 t+ c
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mov eax, [num]8 |' {5 s$ U8 |. ~
and eax, 0xFF& Y C9 j- i) y# Y! F, S
sub eax, 0x300 I0 n7 u$ k6 m3 W0 s
jl ERROR
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cmp eax, 107 z- `* n; c+ G7 j
jl DO_CALC
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ERROR:6 V% Y' \: r9 Q0 l4 Y6 Q. b( n
mov eax, 4 I4 \& r6 v, R$ c
mov ebx, 1; C: l4 s. e4 l8 `) y/ G" y9 s
mov ecx, errMsg
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mov edx, lenErrMsg, R" V p& L+ H+ V6 J7 F
int 80h
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jmp EXIT0 f* ]6 c3 A8 X: c1 U! h
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DO_CALC:1 G A; x: p% t0 }5 H4 U! C
call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.9 M) D+ d1 x# u* }: s+ C
mov [result], eax ; Save the result
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; print result
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mov eax, 4
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mov ebx, 1
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mov ecx, disp1Msg
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mov edx, lenDisp1Msg8 P7 |7 C3 h2 ~1 |
int 80h
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mov eax, 4% ~7 v. U0 b6 Y" B
mov ebx, 1* W( Q+ y! L' L7 Y
mov ecx, num5 j8 b. r- V/ \. M M
mov edx, 1( G1 |* B* s5 D( J1 b* `
int 80h % S z' y& U1 ^
mov eax, 48 Z. `* }9 ^6 j
mov ebx, 1/ Z& T1 A9 B& ~
mov ecx, disp2Msg9 L6 \5 |. F$ S
mov edx, lenDisp2Msg
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int 80h
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; output number9 U: J( m5 ?$ y$ a
mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
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mov byte [buffer+LEN_OF_OUTPUT],0x0a
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lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 $ `* x1 }1 t, G: A* o
ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx: F4 x* @! e4 k; w
div ebx ;DIV EAX/10
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add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER
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dec esi ; store characters in reverse order
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mov [esi],dl; y R7 k& Q* _& Z' `
cmp eax,0 ! Q4 S/ ~! o+ l/ A4 S% o
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII/ @; N B) Z; y m6 e1 v
jmp ASC_LOOP ;ELSE REPEAT
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END_ASC:8 W- s- B ?3 b/ H3 ?. L- m
mov eax, 4
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mov ebx, 1- r6 {1 p7 v) N
mov ecx, esi9 q8 \) c! w: D
lea edx,[buffer+LEN_OF_OUTPUT+1]9 J- K1 w/ }, d) J1 f
sub edx, ecx+ U, _7 s% C D9 s% E
int 80h 5 z0 l0 n, _7 W& N( T
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; Exit code* o, w" ]4 k/ P- ^1 t
EXIT:
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mov eax, 1
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mov ebx, 0" L1 C( U0 @, N4 }
int 80h+ X7 F$ U" [/ R! L
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; Factorial function using recursion# ]$ S* r7 `& Q5 ]! U! J' J' J0 ^
factorial:5 `1 r! L) U3 D1 `1 r. n9 f2 y
; Check if eax is 0 (base condition)( c) L5 s: K7 Z* p
cmp eax, 0
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jz end_recursion
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; Save the current value of eax
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push eax1 @ T" b9 X1 T
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; Decrement eax and call factorial function recursively
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dec eax3 f7 f/ \+ `" A, e3 d+ E: n" T
call factorial4 |6 q( b3 s6 @' }# e1 H& u( t+ [
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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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ret5 G+ e5 ?/ ]" c3 D
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end_recursion:
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; Return 1 when eax is 0 (base condition); p* U- Z/ G" O0 `" @) _4 q2 V; C
mov eax, 13 P8 y4 p4 r S# `2 X% D& F9 d7 f
ret

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nasm -f elf factorial.asm+ Q4 m1 _) N @! y( K% r+ x
ld -m elf_i386 -s -o factorial factorial.o
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./factorial
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; Factorial function using recursion6 e K- Q: J3 a' v1 L! g. \5 D
factorial:
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; Check if eax is 0 (base condition): K( J+ M9 L5 d$ [) U# x' T" i! g, c2 A6 R
cmp eax, 0& @1 A1 q4 M9 @
jz end_recursion. {- w$ g. Z1 x5 [
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; Save the current value of eax4 j1 f" }" p! \3 X. F
push eax% C$ \; K8 s- O, M
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; Decrement eax and call factorial function recursively/ H- L* R3 s8 k# `
dec eax$ `, ?# q7 d) m5 V+ S7 N
call factorial
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; Multiply the result returned in eax with the saved value of eax8 J! ^6 s7 `: {, G
pop ebx' g* W( J, \2 f$ M7 q2 d" F O1 Y
imul eax, ebx
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ret8 S' U' W! G/ S/ o3 ^4 Q) A
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end_recursion:2 F+ _/ s% P' n3 ~% b4 T6 q
; Return 1 when eax is 0 (base condition)
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mov eax, 1/ x G8 {2 K1 u
ret

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