17 lines
1.5 KiB
Rexx
17 lines
1.5 KiB
Rexx
/*REXX program demonstrates the move─to─front algorithm encode/decode symbol table. */
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parse arg xxx; if xxx='' then xxx= 'broood bananaaa hiphophiphop' /*use the default?*/
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one= 1 /*(offset) for this task's requirement.*/
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do j=1 for words(xxx); x= word(xxx, j) /*process a single word at a time. */
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@= 'abcdefghijklmnopqrstuvwxyz'; @@= @ /*symbol table: the lowercase alphabet */
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$= /*set the decode string to a null. */
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do k=1 for length(x); z= substr(x, k, 1) /*encrypt a symbol in the word. */
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_= pos(z, @); if _==0 then iterate /*the symbol position in symbol table. */
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$= $ (_ - one); @= z || delstr(@, _, 1) /*(re─)adjust the symbol table string. */
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end /*k*/ /* [↑] the move─to─front encoding. */
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!= /*set the encode string to a null. */
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do m=1 for words($); n= word($, m) + one /*decode the sequence table string. */
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y= substr(@@, n, 1); != ! || y /*the decode symbol for the N word.*/
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@@= y || delstr(@@, n, 1) /*rebuild the symbol table string. */
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end /*m*/ /* [↑] the move─to─front decoding. */
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say ' word: ' left(x, 20) "encoding:" left($, 35) word('wrong OK', 1 + (!==x) )
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end /*j*/ /*stick a fork in it, we're all done. */
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