用汇编语言实现递归 - 爱吱声

LEN_OF_OUTPUT equ 101 p1 v" ]* C' I2 h1 a0 j
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section .data ;
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userMsg db 'Please enter a single-digit number: ' ;
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lenUserMsg equ $-userMsg ;' A2 }: M, [8 F' \
disp1Msg db 'The factorial of '
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lenDisp1Msg equ $-disp1Msg " Q5 t9 {+ o, y; J: s
disp2Msg db ' is ': a. y- K& J. h }6 V, @& l+ \7 ]7 W, L
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 $-errMsg
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section .bss ;
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num resb 1- }0 J$ @3 b4 o" `
result resd 1
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buffer resb LEN_OF_OUTPUT+1
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section .text ;6 ~) C# z; P: [/ x0 j
global _start
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_start: ; x/ ]# d. W1 A+ M6 }2 j( H! r
mov eax, 4/ V% H& d( m2 Q. U
mov ebx, 1
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mov ecx, userMsg
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mov edx, lenUserMsg, N; a+ O$ O" Y) f
int 80h9 p$ V) o9 U) q* o- \: O
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; read user's input9 T' m- ]* ?7 ]
mov eax, 3
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mov ebx, 0
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mov ecx, num : N- b5 m( m1 c9 \' @) ?. V
mov edx, 1 ; length of input buffer
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int 80h" K( X* _# Y" j
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mov eax, [num]
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and eax, 0xFF
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sub eax, 0x30; N4 B7 Z! ]5 f* a$ ^! m
jl ERROR( S% i2 e; n$ Z2 }1 U/ B7 }
cmp eax, 10
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jl DO_CALC2 |4 A2 U n+ l) c7 D
ERROR: \) Y- e% [: E w
mov eax, 4
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mov ebx, 1
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mov ecx, errMsg
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mov edx, lenErrMsg d6 t% s9 F9 D
int 80h
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jmp EXIT
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DO_CALC:
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call factorial
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; The parameter is in eax. After calling, the result will be stored in eax.' `/ ]8 t( b( z- \
mov [result], eax ; Save the result- S; h& H5 x8 d2 l
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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, lenDisp1Msg
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int 80h 3 K3 i# E; x/ R3 J8 K
mov eax, 4
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mov ebx, 13 \8 m5 |/ \9 y) i! q) r1 Y. k
mov ecx, num0 }8 c% } p6 \1 N
mov edx, 1
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int 80h
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mov eax, 47 D) y! k' f2 T9 v8 ~7 ]. N. n& S! a
mov ebx, 1
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mov ecx, disp2Msg( {( m5 p u+ a- Z, i
mov edx, lenDisp2Msg9 @9 h; A. d" y5 {8 `. o
int 80h + N) k5 l# T- ~% ^
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; output number
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mov eax, [result] ; VALUE THAT I WANT TO CONVERT AND DISPLAY
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mov byte [buffer+LEN_OF_OUTPUT],0x0a* e/ }4 ^8 h4 x: t q
lea esi,[buffer+LEN_OF_OUTPUT]
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mov ebx,10 1 W5 X5 }% Z! P% g6 a9 ?
ASC_LOOP:
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mov edx,0 ; clear dx prior to dividing edx:eax by bx8 v) d$ B+ Y' ^
div ebx ;DIV EAX/103 v# g) k. f$ F; Q: t6 W$ _' V c: J& ]
add edx,0x30 ;ADD 48 TO REMAINDER TO GET ASCII CHARACTER OF NUMBER 6 \+ N" `* k: [: N; X n8 N
dec esi ; store characters in reverse order
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mov [esi],dl2 L$ G- I n+ {! h0 }% Y
cmp eax,0 + i% R# a2 H* X& p, l) v
jz END_ASC ;IF AX=0, END THE PROCEDURE OF NUMBER TO ASCII- V# _* A: {2 q6 f. t
jmp ASC_LOOP ;ELSE REPEAT5 W m6 B$ r! p3 t b, ~6 d
END_ASC:1 p, o) ?+ t) |+ [
mov eax, 4
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mov ebx, 1
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mov ecx, esi
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lea edx,[buffer+LEN_OF_OUTPUT+1]/ X8 W1 C& ^$ x4 X
sub edx, ecx
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int 80h
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; Exit code3 G4 `& v: y( a% \! A
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mov eax, 1
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mov ebx, 0
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int 80h- b4 L6 y, {8 S' x4 W# Z5 O: t
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; Factorial function using recursion
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factorial:
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; Check if eax is 0 (base condition)+ n. k- d/ n; f& E
cmp eax, 0; y S& D" y7 e2 Z$ H0 {" C$ o2 F
jz end_recursion
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; Save the current value of eax
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push eax
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; Decrement eax and call factorial function recursively
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dec eax
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call factorial; R8 c3 l. z: {- n6 o
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; Multiply the result returned in eax with the saved value of eax" x# S0 F) X" E5 Y6 Y
pop ebx& s' F: }+ Z" \2 A- S4 d% S
imul eax, ebx
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ret; V& l9 e2 k7 V/ h
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end_recursion:
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; Return 1 when eax is 0 (base condition)
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mov eax, 13 S# \, {" `3 n
ret

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nasm -f elf factorial.asm1 m, h0 f3 w+ J" U" H! |( R
ld -m elf_i386 -s -o factorial factorial.o3 ^, G# m5 k* `. v1 F6 D
./factorial
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; Factorial function using recursion
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factorial:
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; Check if eax is 0 (base condition)
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cmp eax, 0& `7 G) f" ~/ N/ i
jz end_recursion8 L+ U( O& ?& T
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; Save the current value of eax) ^+ g h8 {3 Z8 r1 I+ O/ H
push eax! q7 C4 v4 T% W6 s# f* Z: x
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; Decrement eax and call factorial function recursively
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dec eax7 o3 G/ e+ _# q% C) t3 F5 }+ A3 H4 ]
call factorial$ C2 G6 E& f5 j, h$ W* d4 v
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; Multiply the result returned in eax with the saved value of eax8 J' e) f& v7 Y9 V. c
pop ebx
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imul eax, ebx
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ret
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end_recursion:$ o4 O+ e2 c! R- q) W9 K
; Return 1 when eax is 0 (base condition)
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mov eax, 1+ G. f. |% ^$ w, {( j! _
ret

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