118 lines
3.2 KiB
NASM
118 lines
3.2 KiB
NASM
GetCurrentLetterPosition: subroutine
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lda #0
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ldx #0
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SelectPassword:
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cpx PasswordInUse
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beq SelectPasswordDone
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adc #24
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inx
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bne SelectPassword
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SelectPasswordDone:
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rts
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DecodePassword: subroutine
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lda #0 ; set up decoding variables
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sta DecodedPasswordOffset
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jsr GetCurrentLetterPosition
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sta CurrentLetterPositionProcess
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ldx #0
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.ReadLetterLoop
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ldy CurrentLetterPositionProcess ; load the next letter of the password
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lda Passwords,y
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sta CurrentLetter ; ...and stick it in a spot in RAM
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ldx #0 ;
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ldy DecodedPasswordOffset
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.FindMatchLoop
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lda Letters,x ; put the next search letter into accumulator
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jsr PushLetterToDecodedPassword ; always push the letter offset onto the decode list
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cmp CurrentLetter ; if it's the same, we're done
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beq .FindMatchExit
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inx
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;cpx #SPACE_LOCATION
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bne .FindMatchLoop
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lda Letters,x ; this is a space
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ldx #SPACE_VALUE
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jsr PushLetterToDecodedPassword
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.FindMatchExit
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inc DecodedPasswordOffset
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iny
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inc CurrentLetterPositionProcess
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cpy #PASSWORD_LENGTH
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bne .ReadLetterLoop
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rts
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ConvertDecodedPasswordToAlternatePassword: subroutine
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ldx #0
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.NextCharacter
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lda DecodedPassword,x
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sta AlternatePassword,x
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cpx #0 ; we can't do anything at position 0
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beq .NotSpaceValue
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cmp #SPACE_VALUE ; not a candidate for modifying the prior value
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beq .SpaceValue
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cmp #SPACE_BECOME_VALUE ; not a candidate for modifying the prior value
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beq .CanBecomeSpaceValue
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bne .NotSpaceValue
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.SpaceValue
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lda #SPACE_BECOME_VALUE
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sta AlternatePassword,x
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jsr galois16
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tay
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and #%00000100
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bne .UseASpace
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dex
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lda DecodedPassword,x
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ora #%00000011
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sta AlternatePassword,x
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inx
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bcs .NotSpaceValue
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.CanBecomeSpaceValue
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; check to make sure both low bits are set on prior
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dex
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lda AlternatePassword,x
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and #%00000011
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bne .DoneBecomingSpace
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inx
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jsr galois16
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tay
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and #%00000100
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bne .NotSpaceValue
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lda #SPACE_VALUE
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sta AlternatePassword,x
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dex
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lda AlternatePassword,x
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cmp #SPACE_VALUE
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.DoneBecomingSpace
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inx
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lda #0
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beq .NotSpaceValue
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.UseASpace
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tya
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and #%00000011
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sta RandomValueForPasswordLetterModification ; y contains the lower bits to use instead
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lda #SPACE_LOCATION
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sta AlternatePassword,x
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dex
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lda DecodedPassword,x
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and #%11111100
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ora RandomValueForPasswordLetterModification
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sta AlternatePassword,x
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inx
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.NotSpaceValue
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inx
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cpx #PASSWORD_LENGTH
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bne .NextCharacter
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.done
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rts
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PushLetterToDecodedPassword: subroutine
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; X contains the letters.indexOf(letter)
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; Y contains the current letter index
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; A will get preserved
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pha
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txa
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sta DecodedPassword,y
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pla
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rts |