"Nice numbers" implementation for pretty range of numerical labels on graph

nice-labels.php

<?php
// @link http://books.google.com/books?id=fvA7zLEFWZgC&pg=PA61&lpg=PA61#v=onepage&q&f=false

function nice_labels( $min, $max, $ticks = 5 ) {

	$range    = nice_number( $max, false );
	$d        = nice_number( $range / ( $ticks - 1 ) );
	$graphmin = floor( $min / $d ) * $d;
	$graphmax = ceil( $max / $d ) * $d;
	$nfrac    = max( array( - floor( log( $d, 10 ) ), 0 ) );

	$output = array();

	foreach ( range( $graphmin, $graphmax + 0.5 * $d, $d ) as $label ) {
		$output[] = round( $label, $nfrac );
	}

	return $output;
}

function nice_number( $num, $round = true ) {

	$exp = floor( log( $num, 10 ) );
	$f   = $num / pow( 10, $exp );

	if ( $round ) {
		if ( $f < 1.5 ) {
			$nf = 1;
		} elseif ( $f < 3 ) {
			$nf = 2;
		} elseif ( $f < 7 ) {
			$nf = 5;
		} else {
			$nf = 10;
		}
	} else {
		if ( $f <= 1 ) {
			$nf = 1;
		} elseif ( $f <= 2 ) {
			$nf = 2;
		} elseif ( $f <= 5 ) {
			$nf = 5;
		} else {
			$nf = 10;
		}
	}

	return $nf * pow( 10, $exp );
}