61 lines
2.2 KiB
Plaintext
61 lines
2.2 KiB
Plaintext
UpperCase:
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;input: A0 = pointer to the string's base address.
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;alters the string in-place.
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MOVE.B (A0),D0 ;load a letter
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BEQ .Terminated ;we've reached the null terminator.
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CMP.B #'a',D0 ;compare to ascii code for a
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BCS .overhead ;if less than a, keep looping.
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CMP.B #'z',D0 ;compare to ascii code for z
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BHI .overhead ;if greater than z, keep looping
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AND.B #%1101111,D0 ;this "magic constant" turns lower case to upper case, since they're always 32 apart.
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.overhead:
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MOVE.B D0,(A0)+ ;store the letter back and increment the pointer.
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;If this isn't an alphabetical character, D0 won't change and this store won't affect the string at all.
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;If it was a letter, it will have been changed to upper case before storing back.
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BRA UpperCase ;next letter
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.Terminated:
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RTS
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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LowerCase:
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MOVE.B (A0),D0 ;load a letter
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BEQ .Terminated ;we've reached the null terminator.
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CMP.B #'A',D0 ;compare to ascii code for A
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BCS .overhead ;if less than A, keep looping.
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CMP.B #'Z',D0 ;compare to ascii code for Z
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BHI .overhead ;if greater than Z, keep looping
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OR.B #%00100000,D0 ;this "magic constant" turns upper case to lower case, since they're always 32 apart.
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.overhead:
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MOVE.B D0,(A0)+ ;store the result and get ready to read the next letter.
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BRA LowerCase ;next letter
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.Terminated:
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RTS
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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ToggleCase:
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MOVE.B (A0),D0 ;load a letter and inc the pointer to the next letter
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BEQ .Terminated ;we've reached the null terminator.
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MOVE.B D0,D1 ;copy the letter
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AND.B #%11011111 ;convert the copy to upper case so we can check it.
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CMP.B #'A',D1 ;compare to ascii code for A
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BCS overhead ;if less than A, keep looping.
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CMP.B #'Z',D1 ;compare to ascii code for Z
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BHI overhead ;if greater than Z, keep looping
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EOR.B #%00100000,D0 ;swaps the case of the letter
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overhead:
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MOVE.B D0,(A0)+ ;store the result
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BRA ToggleCase ;next letter
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.Terminated:
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RTS
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