146 lines
2.2 KiB
NASM
146 lines
2.2 KiB
NASM
;;rotletencrypt
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;;Encrypts a string in rot-n (uses $41 to $5B)
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;;Inputs:
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;; HL: string pointer
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;; A: rot-n
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;;Notes:
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;; Changes string in place.
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rotletencrypt:
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push hl
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push bc
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rotletencryptMod:
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push hl
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ld h, a
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ld l, 'Z' + 1 - 'A' - 1
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call modHL
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ld b, h
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pop hl
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rotletencryptLoop:
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ld a, (hl)
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cp a, $00
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jr z, rotletencryptEnd
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cp a, ' '
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jr z, rotletencryptLD
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add a, b
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cp a, 'Z' + 2
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jr c , rotletencryptLD
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sub a, 'Z' + 2 - 'A'
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rotletencryptLD:
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ld (hl), a
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inc hl
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jr rotletencryptLoop
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rotletencryptEnd:
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ld (hl), $00
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pop bc
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pop hl
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ret
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;;rotletdecrypt
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;;Decrypts a string in rot-n (uses $41 to $5B)
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;;Inputs:
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;; HL: string pointer
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;; A: rot-n
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;;Notes:
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;; Changes string in place.
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rotletdecrypt:
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push hl
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push bc
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rotletdecryptMod:
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push hl
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ld h, a
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ld l, 'Z' + 1 - 'A' - 1
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call modHL
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ld b, h
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pop hl
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rotletdecryptLoop:
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ld a, (hl)
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cp a, $00
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jr z, rotletdecryptEnd
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cp a, ' '
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jr z, rotletdecryptLD
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sub a, b
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cp a, 'A'
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jr nc , rotletdecryptLD
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add a, 'Z' + 2 - 'A'
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rotletdecryptLD:
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ld (hl), a
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inc hl
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jr rotletdecryptLoop
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rotletdecryptEnd:
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ld (hl), $00
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pop bc
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pop hl
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ret
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;;rotasciiencrypt
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;;Encrypts a string in rot-x (uses $00 to $EF)
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;;Inputs:
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;; HL: string pointer
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;; A: x
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;;Notes:
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;; Changes string in place.
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rotasciiencrypt:
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push hl
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push bc
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ld c, 0
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ld c, a
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rotasciiencryptLoop:
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ld a, (hl)
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cp 0
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jr z, rotasciiencryptEnd
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add a, c
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cp 0
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jr nz, rotasciiencryptLd
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inc a
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rotasciiencryptLd:
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ld (hl), a
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inc hl
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cp a, $EF
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jr c, rotasciiencryptLoop
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dec hl
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sub a, $0F
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ld (hl), a
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inc hl
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jr rotasciiencryptLoop
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rotasciiencryptEnd:
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ld (hl), $00
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pop bc
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pop hl
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ret
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;;rotasciidecrypt
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;;Encrypts a string in rot-x (uses $00 to $EF)
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;;Inputs:
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;; HL: string pointer
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;; A: x
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;;Notes:
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;; Changes string in place.
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rotasciidecrypt:
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push hl
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push bc
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ld c, 0
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ld c, a
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rotasciidecryptLoop:
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ld a, (hl)
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cp 0
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jr z, rotasciidecryptEnd
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sub a, c
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cp 0
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jr nz, rotasciidecryptLd
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dec a
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rotasciidecryptLd:
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ld (hl), a
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inc hl
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cp a, $EF
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jr c, rotasciidecryptLoop
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dec hl
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add a, $0F
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ld (hl), a
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inc hl
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jr rotasciidecryptLoop
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rotasciidecryptEnd:
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ld (hl), $00
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pop bc
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pop hl
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ret
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