Try these. fc() is just an Inline C version of f().

I'm pretty sure that they are now correct, but you should verify them yourself.

#! perl -slw
use strict;
use Inline C => << '__C__', NAME => "_627288"; # => CLEAN_AFTER_BUILD 
+=> 0;
#include <stdio.h>

int fc( double x, double y, int d ) {
    double bsize = pow( 4, ( d-1 ) );

    if( x == y )
        return d;
    else if( (int)( x / 4 ) == (int)( y / 4 ) )
        return d-1;
    else if( (int)( x / bsize ) == (int)( y / bsize ) )
        return 1 + fc( fmod( x, bsize ), fmod( y, bsize ), d-1 );
    else
        return     fc( fmod( x, bsize ), fmod( y, bsize ), d-1 );
}

__C__

sub f{
    my( $x, $y, $d ) = @_;
    my $bsize = 4**($d-1);

    if( $x == $y ) {
        return $d
    }
    elsif( int( $x / 4 ) == int( $y / 4 ) ) {
        return $d-1;
    }
    elsif( int( $x / $bsize ) == int( $y / $bsize ) ) {
        return 1 + f( $x % $bsize, $y % $bsize, $d-1 );
    }
    else{
        return     f( $x % $bsize, $y % $bsize, $d-1 );
    }
}
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Using this I have produced plots of 1000x1000 chunks upto level 31 successfully. At that point the coordinates get so large that they blow the limits of doubles. I'm also fairly sure that you are loosing precision long before level 31. At level 16 everything appears to check out.

I don't think any single set of 20 lines of code has ever (in the best part of 30 years), given me as much trouble to wrap my brain around as this!

Hi BrowserUK,

This code is fanstastic! I am impressed.

I hope to be able to fit it to my needs (indices), which I've been dealing with so far by nesting structures, and not completely satisfied with the runtime, maybe this code will be faster, or something inspired by it...

Frank :-)

I went back to your original post to remind myself of what you are doing with the indices...and there it was NOT :)

It was something to do with ordering the indices for a row, stabley, descending by level value in the cell?

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

I verified level 4 after your update and it does not yet match - although close !

Gah. I See where this is headed. I add another ifelse clause to get level 4 right, and then another for level 5...

This has to be possible recursively! It's amazing how something so complex evolves out of such a simple process. It's also amazing how something with so many symmetries and essentially only one dissymmetry could be so hard to generate.

Part of the problem is the shear size the things grow to so rapidly. I wrote a simple png plotter that produces a png of a 1000x1000 chunk and allows you to 'move' around and zoom in--very slowly. But as the level increases, it becomes impossible to keep track of where you are, so it doesn't help much.