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-   -   Code Snippet: a86 Palindrome (http://www.daniweb.com/forums/thread238181.html)

awuja Nov 12th, 2009 9:44 pm
a86 Palindrome
 
Hey guys.. need some help with this; I'm pulling my hair out.. i've trawled these boards but can't find anything that answers my question.

I, like many others before me (so it seems!) am trying to create a program to check for a palindrome.. this is what I have so far.

In the compare part.. it's just not working. I know I'm doing something wrong with SI and DI.. I just don't know what.

Any explanations would be greatly appreciate! :)

Thanks,

awuja
 

  1. JMP START
  2.  
  3. CR equ 13 ; RETURN is 13D ASCII
  4. LF equ 10 ; LINE FEED is 10D ASCII
  5.  
  6. letterUnitCount DB 0
  7. letterTensCount DB 0
  8. vowelCount DB 0
  9.  
  10. getWord: DB "Please enter a word",CR, LF,"$"
  11. letterCountMessage: DB CR, LF, "Number of Characters: ", "$"
  12.  
  13. msg1: DB CR, LF, "  this is palindrome!", "$"
  14. msg2: DB CR, LF, "  this is not a palindrome!", "$"
  15.  
  16. inWord: DB 128 DUP (0)
  17.  
  18. START: 
  19. 	LEA DX,getWord ;Output string asking user for word
  20. 	MOV AH,09h ;DOS call to output string
  21. 	INT 21H ;Execute interrupt 21H
  22.  
  23. KEYBUF: 
  24. 	LEA DI,inWord ;Load inWord start address into DI
  25.  
  26. NEXTCHAR: 
  27. 	MOV AH,01h
  28. 	INT 21H ;Read key pressed and echo to screen
  29.  
  30. 	CMP letterUnitCount, 10
  31. 	JE ROLLOVER
  32.  
  33. UNIT:	
  34. 	INC letterUnitCount
  35.  
  36.  
  37. 	;CMP AL, 65
  38. 	;JE INCRVOWEL
  39. 	;CMP AL, 97
  40. 	;JE INCRVOWEL
  41.  
  42. STORE:	
  43. 	MOV [DI],AL ;store in inWord at position [DI]
  44. 	INC DI ;Make DI point to next byte in inWord
  45. 	CMP AL,0Dh ;Was it the carriage return key?
  46. 	JNZ NEXTCHAR ;NO, get some more characters
  47. 	MOV [byte ptr DI],"$" ;YES, add end of string marker
  48.  
  49. 	MOV SI, DI
  50.  
  51. COMPARE:
  52.  
  53. 	ADD SI, DI
  54. 	DEC SI
  55.  
  56. 	MOV AL, [DI]
  57.  
  58. 	MOV DL, AL
  59. 	MOV AH, 2
  60. 	INT 21h
  61.  
  62. 	MOV BL, [SI]
  63.  
  64. 	MOV DL, BL
  65. 	MOV AH, 2
  66. 	INT 21h
  67.  
  68. 	CMP AL,BL
  69. 	JNE NOTPAL
  70.  
  71. 	INC DI
  72. 	DEC SI
  73. LOOP COMPARE
  74.  
  75. ISPAL:	
  76. 	MOV DX, msg1
  77. 	MOV AH, 09h
  78. 	INT 21h
  79.  
  80. NOTPAL:
  81. 	MOV DX, msg2
  82. 	MOV AH, 09h
  83. 	INT 21h

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