/**
* Converts a length object of one unit into another unit.
* @param HTMLPurifier_Length $length
* Instance of HTMLPurifier_Length to convert. You must validate()
* it before passing it here!
* @param string $to_unit
* Unit to convert to.
* @note
* About precision: This conversion function pays very special
* attention to the incoming precision of values and attempts
* to maintain a number of significant figure. Results are
* fairly accurate up to nine digits. Some caveats:
* - If a number is zero-padded as a result of this significant
* figure tracking, the zeroes will be eliminated.
* - If a number contains less than four sigfigs ($outputPrecision)
* and this causes some decimals to be excluded, those
* decimals will be added on.
*/
function convert($length, $to_unit)
{
/**
* Units information array. Units are grouped into measuring systems
* (English, Metric), and are assigned an integer representing
* the conversion factor between that unit and the smallest unit in
* the system. Numeric indexes are actually magical constants that
* encode conversion data from one system to the next, with a O(n^2)
* constraint on memory (this is generally not a problem, since
* the number of measuring systems is small.)
*/
static $units = array(1 => array('px' => 3, 'pt' => 4, 'pc' => 48, 'in' => 288, 2 => array('pt', '0.352777778', 'mm')), 2 => array('mm' => 1, 'cm' => 10, 1 => array('mm', '2.83464567', 'pt')));
if (!$length->isValid()) {
return false;
}
$n = $length->getN();
$unit = $length->getUnit();
if ($n === '0' || $unit === false) {
return new HTMLPurifier_Length('0', false);
}
$state = $dest_state = false;
foreach ($units as $k => $x) {
if (isset($x[$unit])) {
$state = $k;
}
if (isset($x[$to_unit])) {
$dest_state = $k;
}
}
if (!$state || !$dest_state) {
return false;
}
// Some calculations about the initial precision of the number;
// this will be useful when we need to do final rounding.
$sigfigs = $this->getSigFigs($n);
if ($sigfigs < $this->outputPrecision) {
$sigfigs = $this->outputPrecision;
}
// Cleanup $n for PHP 4.3.9 and 4.3.10. See http://bugs.php.net/bug.php?id=30726
if (strncmp($n, '-.', 2) === 0) {
$n = '-0.' . substr($n, 2);
}
// BCMath's internal precision deals only with decimals. Use
// our default if the initial number has no decimals, or increase
// it by how ever many decimals, thus, the number of guard digits
// will always be greater than or equal to internalPrecision.
$log = (int) floor(log(abs($n), 10));
$cp = $log < 0 ? $this->internalPrecision - $log : $this->internalPrecision;
// internal precision
for ($i = 0; $i < 2; $i++) {
// Determine what unit IN THIS SYSTEM we need to convert to
if ($dest_state === $state) {
// Simple conversion
$dest_unit = $to_unit;
} else {
// Convert to the smallest unit, pending a system shift
$dest_unit = $units[$state][$dest_state][0];
}
// Do the conversion if necessary
if ($dest_unit !== $unit) {
$factor = $this->div($units[$state][$unit], $units[$state][$dest_unit], $cp);
$n = $this->mul($n, $factor, $cp);
$unit = $dest_unit;
}
// Output was zero, so bail out early. Shouldn't ever happen.
if ($n === '') {
$n = '0';
$unit = $to_unit;
break;
}
// It was a simple conversion, so bail out
if ($dest_state === $state) {
break;
}
if ($i !== 0) {
// Conversion failed! Apparently, the system we forwarded
// to didn't have this unit. This should never happen!
return false;
}
// Pre-condition: $i == 0
// Perform conversion to next system of units
$n = $this->mul($n, $units[$state][$dest_state][1], $cp);
$unit = $units[$state][$dest_state][2];
$state = $dest_state;
// One more loop around to convert the unit in the new system.
}
// Post-condition: $unit == $to_unit
if ($unit !== $to_unit) {
return false;
}
// Useful for debugging:
//echo "<pre>n";
//echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n";
$n = $this->round($n, $sigfigs);
if (strpos($n, '.') !== false) {
$n = rtrim($n, '0');
}
$n = rtrim($n, '.');
return new HTMLPurifier_Length($n, $unit);
}