public function convert($length, $to_unit)
{
if (!$length->isValid()) {
return false;
}
$n = $length->getN();
$unit = $length->getUnit();
if ($n === '0' || $unit === false) {
return new HTMLPurifier_Length('0', false);
}
$state = $dest_state = false;
foreach (self::$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;
}
// 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
$dest_unit = self::$units[$state][$dest_state][0];
}
// Do the conversion if necessary
if ($dest_unit !== $unit) {
$factor = $this->div(self::$units[$state][$unit], self::$units[$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, self::$units[$state][$dest_state][1], $cp);
$unit = self::$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);
}