ioccc/1989/westley/README.md

Most algorithms in one program:

Merlyn LeRoy (Brian Westley)
Starfire Consulting
1026 Blair Ave.
St. Paul, MN  
55104  
USA

http://www.westley.org

To build:

make all

Cody Boone Ferguson was able to get this to partially work with clang; clang requires that the second, third and fourth args to main() be char **. Only westley.c and ver0.c (see below) will compile with clang. It's possible to get ver1.c to compile too but this causes problems with generating the output of the remaining files so we have opted, at least for now, to not do that, as it does not have to output just source code. He notes that the original source code sometimes segfaults with ver2 which also happens with the fix but it'll only compile with a compiler that does not require the second, third and fourth args of main() to be a char **. Thank you Cody for your help!

Try:

	./westley < westley.c > ver0.c
	./westley 1 < westley.c > ver1.c
	./westley 1 2 < westley.c > ver2.c
	./westley 1 2 3 < westley.c > ver3.c

Try compiling and running the 4 resulting programs. To compile try:

	make ver0
	make ver1
	make ver2
	make ver3

Judges notes:

There is a secret way to get ONE of the versions to print out "Hello, world!\n". Can you find how to do it?

Selected notes from the author:

This is a filter. If it is run with no arguments, it copies stdin to stdout. With one argument, it ROT13's stdin to stdout. With two arguments, it reverses stdin to stdout. With three arguments, it does both. It requires the ASCII character set, with all characters being in 0..255, and EOF must be -1. Also requires two's complement (I think).

The source code will run if ROT13'ed and/or reversed, using a different algorithm for each version (hereafter referred to as ver0 (original), ver1 (ROT13), ver2 (reversed), and ver3 (ROT13 and reversed)).

When compiling these versions, one needs to define 'trgpune' in the compile line (which the Makefile now has). Example:

	cc -Dtrgpune=putchar ver3.c -o ver3

"trgpune" is the ROT13 of getchar(), so getchar() and putchar() are exchanged in the ROT13 counterpart. It is easy to see that this is unavoidable. I must have a #define for a library function; otherwise I would have an unidentified extern for the ROT13 version. If I then define this function, it won't link in the library version for the ORIGINAL code, since my definition will supersede the library function. Hence, the compiler option gives me putchar(), and allows me to use getchar(). I pass a dummy argument to getchar() to eliminate "variable number of args" from lint (unless it checks against the library). Otherwise, all versions lint reasonably (main returns random value & constant in conditional context [when I check for ROT13 version] is all it complains about).

ver0 and ver1 use a range check and a calculation to do ROT13, while ver2 and ver3 use table lookup. All versions contain main() and it's ROT13 fn, znva(). ver0/ver1 [ver2/ver3] are (of course) syntactically identical, since the syntax is in the non-alphabetic characters. However, since one program starts at main() while it's ROT13 counterpart starts at znva(), znva() calls main (znva() is also used for output).

All versions use recursion to work. If the program is NOT reversing it's output, it prints out the (possibly ROT13'd) character before recursing, otherwise it prints it out afterward (or doesn't recurse at all when EOF is reached). Since most of this code is identical, it is put into znva() and called with a first parameter of 0 as a flag (as "main()", it's first argument (argc) must be at least one).

I can't use any flow control. If I used if(), I would have a function vs() to define in the ROT13 version. But a function called vs() turns into a function called if() in the original, so it can't be done. Therefore, I do:

	expr1 && expr2 && (expr3=etc);

which is the same as:

	 if (expr1 && expr2) expr3=etc;

A/UX on the Macintosh doesn't get this right; it evaluates ALL expressions if they aren't in an assignment or conditional statement. This might warrant a warning, since other compilers may do this. I found MANY compilers botched:

	expr1 && (expr2,expr3);

expr2 was OFTEN evaluated even if expr1 was false. I removed such statements to make it more portable.

The variable names are worth noting:

	 'irk' and  'vex' are ROT13 pairs and are synonyms.
	'Near' and 'Arne' are ROT13 pairs and are anagrams.
	'NOON' and 'ABBA' are ROT13 pairs and are palindromes.
	'tang' and 'gnat' are both ROT13 and palindrome pairs!

Normally (!), a reversible C program is done thus:

	/**/ forward code /*/ edoc drawkcab /**/

If your compiler nests comments, it will get this wrong. However, I have made some bits of the code palindromic, (or different, but reversible) so it is more like:

	/**/forward/*//**/ palindromic /**//*/drawkcab/**/

The code can therefore be interlaced. There are eight such palindromic bits. You can find them within the /*//**/ /**//*/ pairs.

The body of the code of ver0 and ver1 is a large lumpy 'K' (for Kernighan); the code of ver2 and ver3 is a flat-topped and lumpier 'R' (for Ritchie). Judicious use of spaces and tabs helped here. It barely fits on an 80x24 screen. Squint. Note that the code must start with a blank line, or the reversed version will lack a terminating newline.

Copyright and CC BY-SA 4.0 License:

This file is Copyright (c) 2023 by Landon Curt Noll. All Rights Reserved. You are free to share and adapt this file under the terms of this license:

Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)

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