Data commit

Task/Vigen-re-cipher/XPL0/vigen-re-cipher.xpl0

@@ -0,0 +1,21 @@
+code ChIn=7, ChOut=8;
+int  Neg, C, Len, I, Key;
+char KeyWord(80);
+[Neg:= false;                                   \skip to KEYWORD
+repeat C:= ChIn(8);  if C=^- then Neg:= true;  until C>=^A & C<=^Z;
+Len:= 0;                                        \read in KEYWORD
+repeat KeyWord(Len):= C-^A;  Len:= Len+1;  C:= ChIn(8);  until C<^A ! C>^Z;
+I:= 0;                                          \initialize cycling index
+repeat  C:= ChIn(1);
+        if C>=^a & C<=^z then C:= C-$20;        \capitalize
+        if C>=^A & C<=^Z then                   \discard non-alphas
+            [Key:= KeyWord(I);  I:= I+1;  if I>=Len then I:= 0;
+            if Neg then Key:= -Key;             \decrypting?
+            C:= C+Key;
+            if C>^Z then C:= C-26
+            else if C<^A then C:= C+26;
+            ChOut(0, C);
+            ];
+until   C=$1A;  \EOF
+ChOut(0, $1A);  \encrypted file must end with EOF otherwise the decode will hang
+]