ioccc/2001/westley/README.md

## To build:

``` <!---sh-->
    make
```

There are two additional programs based on the author's remarks and the original
version, provided as alternate code as it might be less portable. See [sorted
code](#sorted-code), [punch card code](#punch-card-code) and [alternate
code](#alternate-code) below.


### Bugs and (Mis)features:

The current status of this entry is:

> **STATUS: uses gets() - change to fgets() if possible**<br>
> **STATUS: main() has only one arg - try and make it have 2 or 3**

For more detailed information see [2001/westley in bugs.html](../../bugs.html#2001_westley).


## To use:

``` <!---sh-->
    ./westley 2>/dev/null
    # enter some input, terminate with EOF

    echo foo | ./westley 2>/dev/null

    ./westley < westley.c 2>/dev/null
```


## Try:

``` <!---sh-->
    ./try.sh
```


## Sorted code:

The author stated that one can sort (ignoring leading blanks i.e. `sort -b`) the
code by line and it will always sort the order of the input.

This is generated and compiled by default; use `westley.sort` as you would
`westley` above.


## Punch card code:

The author also stated that if you just sort the code (`sort westley.c`) you'll
get a version that just prints out the punch card. The `westley.punch.c`
(generated by `make` via `sort westley.c`) code is specifically so that Westley
can punch everyone in the face! :-) This is also compiled by default.


### Punch card try:

``` <!---sh-->
    echo 'Brian Westley does it again!' | ./westley.punch 2>/dev/null
```


## Alternate code:

An alternate version of this entry, [westley.alt.c](%%REPO_URL%%/2001/westley/westley.alt.c), is provided.
This alternate code might be less portable.


### Alternate build:

``` <!---sh-->
    make alt
```


### Alternate use:

Use `westley.alt` as you would `westley` above.


## Judges' remarks:

Try copying the source to a new file and changing around the
order of the lines.  Does it produce the exact same output?

By changing the order of the source, figure out in how many different
ways this program can transform input to output.

This assortment of obfuscated lines takes [position-independent
code](https://en.wikipedia.org/wiki/Position-independent_code) to a new level! :-)

We find it amazing that with just 28 lines of code (not counting comments and
blank lines) there are `28!` or `304,888,344,611,713,860,501,504,000,000`
versions of the program, all valid C!


## Author's remarks:

[Punch cards](https://en.wikipedia.org/wiki/Punched_card), or Hollerith cards,
were becoming obsolete just as C was becoming more popular[^1]; this is rather
unfortunate, because C has an advantage over many other languages when it comes
to punch cards - C programs can be written to be "drop proof".

Consider the following C program:

``` <!---c-->
    main(){a();b();c();}
    a(){printf("A");}
    b(){printf("B");}
    c(){printf("C");}
```

This program will compile and run no matter what order the
lines are in.  If you punch it on cards (one line of code per
card, naturally) and drop them, you don't need to put them in
any particular order[^2]; it will always produce `ABC` as output.

You can also use global variables:

``` <!---c-->
    char *greet = "Hello, world!";
    char *greet; main(){puts(greet);}
```

It would be trivial to write an entire C program that is
"drop proof" using the above techniques; surprisingly, it's
possible to write a program that will always compile but
behave differently depending on the line order:

``` <!---c-->
    test(a,b){return a;}
    #define test(a,b) test(b,a)
    main(){if (test(0,1)) printf("T"); else printf("F");}
```

This program will print out `T` if the `#define` statement
falls between the declaration of `test()` and its use in
`main()`, otherwise it will print out `F`.  Furthermore,
you can use the same call to `test()` repeatedly in
different lines to return different values:

``` <!---c-->
    #define test(x,y) test(y,x)
    main(){int i=0;a(&i);b(&i);c(&i);d(&i);printf("%d\n",i);}
    a(i)int*i;{if (test(0,1)) *i += 1;}
    b(i)int*i;{if (test(0,1)) *i += 2;}
    c(i)int*i;{if (test(0,1)) *i += 4;}
    d(i)int*i;{if (test(0,1)) *i += 8;}
    test(x,y){return x;}
```

If you enter the above program on punch cards, throw them
up in the air, gather them up, and run it, you will get
a number from 0 to 15 printed out.  Now *that's* a random
number generator...

Of course, there are drawbacks to C programming on punch
cards; an 80-character line limit can be restricting, and
(to be maximally portable) you need to use trigraphs for
the characters `^[]{}\` (these aren't found on every
keypunch, and have various encodings).

My C program entry does the following:

1. Reads in lines.

2. Rearranges the lines, or not.
    - if it rearranges the lines, they are sorted or scrambled.

3. Reverses the order of the lines, or not.

4. Prints out the lines as either text or
[EBCDIC](https://en.wikipedia.org/wiki/EBCDIC) punch cards.

The code, as written, scrambles the input and prints it out
as normal text, so you can simulate 'dropping' the cards.
You can repeatedly scramble the code to get all 12 variants
(but the scrambling isn't very random; it's just a bubble
sort with a random number, so some variants are more common
than others).  You can also just swap the arguments in the
calls to `t()` in all combinations to get all the variations.

If you sort the lines, you will get the version that just
prints out the input as punch cards (you will need to display
at least 82 columns of text, or clip the last few chars by
piping it through `sed s/...$//`).  If you use this on the
original code, you will see that it spells out `HOLLERITH`
when punched on cards (you can see the tall, thin letters
spelling out `HOLLERITH` if you turn the C code sideways).
You will also see why `/KC 0000 K` is a `Hollerith emoticon`.
Unrecognized characters are punched as a lace column.
(You can see an ASCII simulation of the code as punch cards
by looking at `card.gif`.)

For a nice test pattern, try

```
    &-0123456789ABCDEFGHIJKLMNOPQR/STUVWXYZ:#@'=".<(+|!$*);,%_>?abcmnoxyz^[]{}\
```

If you want to analyze the program, sorting the lines while
ignoring leading blanks works best (`sort -b`).  This will
produce the version that just reverses the line order, and
the routines in the code are in a sensible order.

This program should work on EBCDIC computers.  It assumes
that the `time_t` ptr param to `time(3)` will work with an `int`
ptr, and that "passing through" a `char[][]` array as a simple
`char *` is OK.  Your compiler MUST understand trigraphs, or it
will miss the trigraph backslash before the double quote in
the `K` string and complain about a malformed string; for GNU
C, use `-ansi` or `-trigraphs`.  Entering a line of more than 80
characters, or more than 81 lines, will jam the card reader.

I've used the `a[b]` ==> `*(a+b)` trick, because this is
actually shorter than the trigraph version of `a??(b??)`.

With 28 lines of code (not counting the blank lines or the
comment), there are technically `28!` different programs, or
`304,888,344,611,713,860,501,504,000,000` different versions,
all legal C.

[^1]: except in Florida voting machines

[^2]: all cards must be face down, nine-edge first, of course.


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