Data update

Task/Substitution-cipher/ALGOL-68/substitution-cipher.alg

@@ -0,0 +1,56 @@
+BEGIN # subsitiution cipher #
+                            #  abcdefghijklmnopqrstuvwxyz   #
+    STRING substitute lower = "dthnxkmqrwzseglyoaubjpcfiv";
+    STRING substitute upper = "TKXMGVUPOIRFDEJZNYWCAQSLBH";
+                            #  ABCDEFGHIJKLMNOPQRSTUVWXYZ   #
+
+    PROC encrypt = ( STRING plain text )STRING:
+         BEGIN
+            PROC encode = ( CHAR c, base, STRING code )CHAR:
+                 code[ ( ABS c - ABS base ) + LWB code ];
+            STRING result := plain text;
+            FOR pos FROM LWB result TO UPB result DO
+                CHAR c = result[ pos ];
+                IF   c >= "A" AND c <= "Z" THEN
+                    result[ pos ] := encode( c, "A", substitute upper )
+                ELIF c >= "a" AND c <= "z" THEN
+                    result[ pos ] := encode( c, "a", substitute lower )
+                FI
+            OD;
+            result
+         END # encrypt # ;
+
+    PROC decrypt = ( STRING cipher text )STRING:
+         BEGIN
+            PROC decode = ( CHAR c, base, STRING code )CHAR:
+                 BEGIN
+                    INT c pos := 0;
+                    char in string( c, c pos, code );
+                    REPR ( ABS base + ( c pos - 1 ) )
+                 END # decode # ;
+            STRING result := cipher text;
+            FOR pos FROM LWB result TO UPB result DO
+                CHAR c = result[ pos ];
+                IF c >= "A" AND c <= "Z" THEN
+                    result[ pos ] := decode( c, "A", substitute upper )
+                ELIF c >= "a" AND c <= "z" THEN
+                    result[ pos ] := decode( c, "a", substitute lower )
+                FI
+            OD;
+            result
+         END # decrypt # ;
+
+    PROC test cipher = ( STRING plain text )VOID:
+         IF STRING encoded = encrypt( plain text );
+            STRING decoded = decrypt( encoded );
+            print( ( plain text, " -> ", encoded, newline ) );
+            print( ( encoded,    " -> ", decoded, newline ) );
+            decoded /= plain text
+         THEN
+            print( ( "**** encode/decode problem", newline ) )
+         FI # test cipher # ;
+
+    test cipher( "Sphinx of Black Quartz, judge my vow" );
+    test cipher( "ABCDEFGHIJKLMNOPQRSTUVWXYZzyxwvutsrqponmlkjihgfedcba" )
+
+END