In his infamous rant Why Pascal Is Not My Favorite Programming Language Brian Kernighan says "There is a paucity of operators ... In particular, there are no bit-manipulation operators (AND, OR, XOR, etc.). I simply gave up trying to write the following trivial encryption program in Pascal:

     i := 1;
     while getc(c) <> ENDFILE do begin
             putc(xor(c, key[i]));
             i := i mod keylen + 1
     end

because I couldn't write a sensible 'xor' function."

The amazing part of this statement is that I cannot fathom why he found it so hard to write an xor function. It's simply not that hard. In this post we take up the challenge.

We will assume that Kernighan's compiler did not have the type Byte and this may one source of his problem. However, Byte is simply a subrange of the integers (0 .. 255) so this is easily surmounted. We can also safely assume that he had access to the Boolean operators NOT, OR and AND...