Initial data commit

Task/LZW-compression/BBC-BASIC/lzw-compression.basic

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+      plaintext$ = "TOBEORNOTTOBEORTOBEORNOT"
+      encodeLZW$ = FNencodeLZW(plaintext$)
+      FOR i% = 1 TO LEN(encodeLZW$) STEP 2
+        PRINT ; ASCMID$(encodeLZW$,i%) + 256*ASCMID$(encodeLZW$,i%+1) " " ;
+      NEXT
+      PRINT ' FNdecodeLZW(encodeLZW$)
+      END
+
+      DEF FNencodeLZW(i$)
+      LOCAL c%, d%, i%, l%, o$, w$, dict$()
+      DIM dict$(4095)
+      FOR i% = 0 TO 255 : dict$(i%) = CHR$(i%) : NEXT
+      l% = i%
+      i% = 1
+      w$ = LEFT$(i$,1)
+      REPEAT
+        d% = 0
+        REPEAT
+          c% = d%
+          IF i% > LEN(i$) EXIT REPEAT
+          FOR d% = 1 TO l%-1
+            IF w$ = dict$(d%) EXIT FOR
+          NEXT d%
+          IF d% < l% i% += 1 : w$ += MID$(i$, i%, 1)
+        UNTIL d% >= l%
+        dict$(l%) = w$ : l% += 1 : w$ = RIGHT$(w$)
+        o$ += CHR$(c% MOD 256) + CHR$(c% DIV 256)
+      UNTIL i% >= LEN(i$)
+      = o$
+
+      DEF FNdecodeLZW(i$)
+      LOCAL c%, i%, l%, o$, t$, w$, dict$()
+      DIM dict$(4095)
+      FOR i% = 0 TO 255 : dict$(i%) = CHR$(i%) : NEXT
+      l% = i%
+      c% = ASC(i$) + 256*ASCMID$(i$,2)
+      w$ = dict$(c%)
+      o$ = w$
+      IF LEN(i$) < 4 THEN = o$
+      FOR i% = 3 TO LEN(i$) STEP 2
+        c% = ASCMID$(i$,i%) + 256*ASCMID$(i$,i%+1)
+        IF c% < l% t$ = dict$(c%) ELSE t$ = w$ + LEFT$(w$,1)
+        o$ += t$
+        dict$(l%) = w$ + LEFT$(t$,1)
+        l% += 1
+        w$ = t$
+      NEXT
+      = o$