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...

I've always recommended that programmers make it a point to read this classic by Kernighan and Plauger. I'm now in the process of reading it again. I had to request an interlibrary load to get it.

Upon re-reading it (I'm now up to chapter 3) I find it terribly dated. The examples are all in Fortran and PL/1 (PL/I?). One of the "rules" set forth is "avoid the Fortran arithmetic IF," a good piece of advise if you happen to be programming in Fortran but of little use if you are using C++ or Pascal.

The first chapters of the book seem to deal almost exclusively with when and when not to use GOTO and how to use it when you do. Again advise aimed at Fortran programmers who, lacking WHILE and IF..THEN..ELSE, had no choice but to use GOTO, and at PL/1 programs who could avoid the GOTO but often didn't, producing "Fortran with semicolons."...

Software Tools in Pascal is a rewrite of Software Tools by Brian W. Kernighan and P. J. Plauger. In the first book Kernighan and Plauger wrote their programs in RatFor, a dialog of Fortran implemented via a preprocessor, which gave Fortran a C-like syntax. In attempting to repeat this effort using Pascal, Kernighan apparently developed a dislike for the language and in the same year Software Tools in Pascal was published he also published his famous rant Why Pascal is Not My Favorite Programming Language. I will address this rant in a later post.

My intention here is to re-write the programs in Software Tools in Pascal using Turbo Pascal, an implementation of the language that became a de-facto standard. I will admit up front that this effort is entirely academic. I'm doing it for fun. Still, some people might find it useful. The tools K&P presented were, even at that time, pretty much available pre-packaged in DOS and Unix, so even the original books were something of an academic effort...