#! perl -slw
use strict;

sub log10{ log( $_[0] ) / log( 10 ) }

sub ticks {
    my( $start, $end, $n ) = @_;
    $n ||= 10;
    my $range = $end - $start;
    $range += $range / $n;
    my $interval = $range / $n;
    $interval  = 10**int( log10( $interval ) );
    $interval *= 10 while ( $range / $interval ) > ( $n * 2 );
    $interval /=  2 while ( $range / $interval ) < ( $n / 2 );
    $start = int( $start / $interval ) * $interval;

    my @ticks;
    while( $start < ( $end + $interval ) ) {
        push @ticks, $start;
        $start += $interval;
    }
    return @ticks;
}


for my $range (
    [0,9], [0.123,8.673], [0.022, 0.086],
    [1_123_345_456, 1_124_246_357.5], [1_123_345_456, 1_123_346_357.5],
    [ 0.00011, 0.00041],
) {
    for my $n ( 0, 4, 5, 8 , 10, 15, 16, 20, 21 ) {
        my @ticks = ticks( @$range, $n );

        printf "from:%12.12g to %12.12g by:%2u -> [%2u][ %s ]\n",
            @$range, $n, scalar( @ticks ), join ' ', map{
                my $s = sprintf( "%.8g", $_ ); $s =~ s[e([+-])0*([1-9]+)]['e' . ($1 eq '-' ? '-' : '') . $2]e;
                $s;
            } @ticks;

    }
}