*-----------------------------------------------------------
* Program    :
* Written by :
* Date       :
* Description:
*-----------------------------------------------------------
    ORG $1000
START:              ; first instruction of program
    move.l  #$7FFE,SP   ; initialise stack pointer
    move.b  #0,d1       ; Turn off the auto echo
    move.b  #12,d0
    trap    #15

    move.l  #$2000,a1   ; move address $2000 into a1

    move.l  #string1,a0 ;Print user promt1
prompt1:
    move.b  (a0)+,d1
    beq input
    move.b  #6,d0
    trap    #15
    bra prompt1

input:
    move.b  #5,d0       ; take character input
    trap    #15
    move.b  #6,d0       ; print the charactrer input
    trap    #15

    cmp.b   #cr,d1      ; escape loop if a cr entered
    beq length

    move.b  d1,(a1)+    ; increment array
    add.b   #1,d2       ; add to length counter
    bra input       ; branch to start of loop

length:
    move.b  #cr,d1      ; Print a carriage return
    move.b  #6,d0
    trap    #15
    move.b  #lf,d1      ; Print a line feed
    move.b  #6,d0
    trap    #15

    move.b  d2,d1       ; Print the sting length
    move.b  #3,d0
    trap    #15

    move.l  #string2,a0 ; Print user promt2
prompt2:
    move.b  (a0)+,d1
    beq output
    move.b  #6,d0
    trap    #15
    bra prompt2

output:             ; Print the users input
    move.l  #$2000,a0
next:
    cmp.b   d3,d2
    beq palcheck
    move.b  (a0)+,d1
    move.b  #6,d0
    trap    #15
    add.b   #$1,d3
    bra next

palcheck:           ; Check for palindrome
    move.l  #$2000,a2   ; Set up two arrays
    move.l  #$2000,a3
    sub.b   #$1,d3      ; minus one for second array reference
    add.l   d3,a3
palloop:
    cmp.b   d6,d2       ; compare loop iteration to array size
    beq ispal
    move.b  (a2),d4
    move.b  (a3),d5
    add.l   #$1,a2      ; increment a2
    sub.l   #$1,a3      ; decrement a3
    cmp.b   d4,d5
    bne notpal
    add.b   #$1,d6      ; increment loop interation
    bra palloop

ispal:              ; Print string3
    move.b  #cr,d1      ; Print a carriage return
    move.b  #6,d0
    trap    #15
    move.b  #lf,d1      ; Print a line feed
    move.b  #6,d0
    trap    #15
    move.l  #string3,a0
ispaloutput:
    move.b  (a0)+,d1
    beq reinit
    move.b  #6,d0
    trap    #15
    bra ispaloutput

notpal:             ; Print string4
    move.b  #cr,d1      ; Print a carriage return
    move.b  #6,d0
    trap    #15
    move.b  #lf,d1      ; Print a line feed
    move.b  #6,d0
    trap    #15
    move.l  #string4,a0
notpaloutput:
    move.b  (a0)+,d1
    beq reinit
    move.b  #6,d0
    trap    #15
    bra notpaloutput

reinit:             ; reinitilise the registers
    move.b  #$0,d0
    move.b  #$0,d1
    move.b  #$0,d2
    move.b  #$0,d3
    move.b  #$0,d4
    move.b  #$0,d5
    move.b  #$0,d6

    move.l  #$0,a0
    move.l  #$0,a1
    move.l  #$0,a2
    move.l  #$0,a3

    move.b  #cr,d1      ; Print a carriage return
    move.b  #6,d0
    trap    #15
    move.b  #lf,d1      ; Print a line feed
    move.b  #6,d0
    trap    #15
    move.b  #6,d0
    trap    #15

    bra start       ; Loop back to start

    MOVE.B  #9,D0
    TRAP    #15     ; halt simulator



* Variables and Strings

    ORG $2500
string1 dc.b    'Please enter a string and press return: ',null
string2 dc.b    ' characters entered: ',null
string3 dc.b    'It was a palindrome',null
string4 dc.b    'It was not a palindrome',null
null    equ $00
cr  equ $0D
lf  equ $0A

    END START       ; last line of source

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