23 lines
2.2 KiB
Rexx
23 lines
2.2 KiB
Rexx
/*REXX program supports the Caesar cypher for the Latin alphabet only, no punctuation */
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/*──────────── or blanks allowed, all lowercase Latin letters are treated as uppercase.*/
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parse arg key .; arg . p /*get key & uppercased text to be used.*/
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p=space(p,0) /*elide any and all spaces (blanks). */
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say 'Caesar cypher key:' key /*echo the Caesar cypher key to console*/
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say ' plain text:' p /* " " plain text " " */
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y=Caesar(p, key); say ' cyphered:' y /* " " cyphered text " " */
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z=Caesar(y,-key); say ' uncyphered:' z /* " " uncyphered text " " */
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if z\==p then say "plain text doesn't match uncyphered cyphered text."
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exit /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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Caesar: procedure; arg s,k; @='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
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ak=abs(k) /*obtain the absolute value of the key.*/
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L=length(@) /*obtain the length of the @ string. */
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if ak>length(@)-1 | k==0 then call err k 'key is invalid.'
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_=verify(s,@) /*any illegal characters specified ? */
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if _\==0 then call err 'unsupported character:' substr(s, _, 1)
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if k>0 then ky=k+1 /*either cypher it, or ··· */
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else ky=L+1-ak /* decypher it. */
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return translate(s, substr(@||@,ky,L),@) /*return the processed text. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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err: say; say '***error***'; say; say arg(1); say; exit 13
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