ioccc/2001/ollinger

Best primal ASCII graphics:

Nicolas Ollinger
Ecole Normale Superieure de Lyon
LIP, ENS Lyon
46, allée d'Italie
69364 Lyon Cedex 07
France

http://www.ens-lyon.fr/~nollinge/

Judges' Comments:

To build:

	make ollinger

 Try:

In a large window, say 200 chars wide and 100 high (200x100)
with a tiny font, try:

    ./ollinger 1000 | cut -c -200


 Do get lost in the programs line of thought!  :-)

Selected Author's Comments:

What's this?
------------

What do you see? On the left, you will see an enumeration of all successive
primes from 2 to the parameter you gave to the program. On the right part,
you can see the sieve used to find these primes. The big diagonals from
right to left are used to erase composed numbers. When no diagonal crosses
a number, then the left cell take value 1 and the number is prime.

The parallel version of this algorithm works in real time n. This C
sequential version is slower as it works in O(n*log n). But you have some
nice picture instead... the cost is a constant number of operation for each
character printed on the screen.


Why do you wrote it?
--------------------

Let's just quote the FAQ :

Q: Are there types of entries that are submitted so frequently that the
   judges get tired of them?

A: Yes, there are types of entries that show up over and over again.
   The guidelines say:

            We tend to dislike programs that:
            are similar to previous winners

      We like variety. However too often we see (please look at the winning
      examples given to be aware of the level of the competition):

(snip)

            generating small primes (below is the list of all
                                     prime related winners)
                  1985/august
                  1988/applin
                  1994/weisberg
                  1995/makarios
                  1996/dalbec
                  2000/bellard

            As you can see, just a list of primes (let alone small primes)
             does not cut it anymore.

(snip)

            entries that use some complex state machine/table to print
            something

                  1988/isaak
                  1988/phillipps

            Unbeaten for 12 years and counting...

I think this is enough motivation for trying to submit a program which uses
some complex state machine/table to generate small primes and print them.


The way it works
----------------

This program simply prints the space-time diagram of some particular
cellular automaton. The automaton is a 9-state automaton by Korec in 1998.
It is an optimization of an old automaton for recognizing primes designed
by Fischer in 1965.

The table of the automaton is encoded into the string e and consists of
345 transitions of the kind f(left,middle,right). This encoding into e
is obfuscated to reduce its size, restrict it to characters 32 to 127 and
guarantee a constant time.

The main loop simply iterates this transition function on each cell.

"The rest is silence" (Hamlet, V.2)

Enjoy!