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<?php |
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/** |
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* Class for converting between different unit-lengths as specified by |
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* CSS. |
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*/ |
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class HTMLPurifier_UnitConverter |
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{ |
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const ENGLISH = 1; |
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const METRIC = 2; |
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const DIGITAL = 3; |
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/** |
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* Units information array. Units are grouped into measuring systems |
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* (English, Metric), and are assigned an integer representing |
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* the conversion factor between that unit and the smallest unit in |
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* the system. Numeric indexes are actually magical constants that |
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* encode conversion data from one system to the next, with a O(n^2) |
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* constraint on memory (this is generally not a problem, since |
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* the number of measuring systems is small.) |
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*/ |
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protected static $units = array( |
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self::ENGLISH => array( |
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'px' => 3, // This is as per CSS 2.1 and Firefox. Your mileage may vary |
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'pt' => 4, |
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'pc' => 48, |
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'in' => 288, |
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self::METRIC => array('pt', '0.352777778', 'mm'), |
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), |
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self::METRIC => array( |
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'mm' => 1, |
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'cm' => 10, |
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self::ENGLISH => array('mm', '2.83464567', 'pt'), |
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), |
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); |
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/** |
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* Minimum bcmath precision for output. |
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* @type int |
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*/ |
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protected $outputPrecision; |
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/** |
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* Bcmath precision for internal calculations. |
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* @type int |
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*/ |
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protected $internalPrecision; |
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/** |
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* Whether or not BCMath is available. |
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* @type bool |
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*/ |
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private $bcmath; |
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public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) |
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{ |
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$this->outputPrecision = $output_precision; |
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$this->internalPrecision = $internal_precision; |
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$this->bcmath = !$force_no_bcmath && function_exists('bcmul'); |
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} |
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/** |
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* Converts a length object of one unit into another unit. |
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* @param HTMLPurifier_Length $length |
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* Instance of HTMLPurifier_Length to convert. You must validate() |
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* it before passing it here! |
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* @param string $to_unit |
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* Unit to convert to. |
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* @return HTMLPurifier_Length|bool |
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* @note |
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* About precision: This conversion function pays very special |
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* attention to the incoming precision of values and attempts |
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* to maintain a number of significant figure. Results are |
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* fairly accurate up to nine digits. Some caveats: |
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* - If a number is zero-padded as a result of this significant |
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* figure tracking, the zeroes will be eliminated. |
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* - If a number contains less than four sigfigs ($outputPrecision) |
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* and this causes some decimals to be excluded, those |
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* decimals will be added on. |
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*/ |
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public function convert($length, $to_unit) |
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{ |
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if (!$length->isValid()) { |
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return false; |
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} |
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$n = $length->getN(); |
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$unit = $length->getUnit(); |
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if ($n === '0' || $unit === false) { |
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return new HTMLPurifier_Length('0', false); |
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} |
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$state = $dest_state = false; |
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foreach (self::$units as $k => $x) { |
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if (isset($x[$unit])) { |
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$state = $k; |
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} |
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if (isset($x[$to_unit])) { |
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$dest_state = $k; |
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} |
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} |
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if (!$state || !$dest_state) { |
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return false; |
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} |
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// Some calculations about the initial precision of the number; |
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// this will be useful when we need to do final rounding. |
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$sigfigs = $this->getSigFigs($n); |
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if ($sigfigs < $this->outputPrecision) { |
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$sigfigs = $this->outputPrecision; |
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} |
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// BCMath's internal precision deals only with decimals. Use |
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// our default if the initial number has no decimals, or increase |
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// it by how ever many decimals, thus, the number of guard digits |
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// will always be greater than or equal to internalPrecision. |
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$log = (int)floor(log(abs($n), 10)); |
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$cp = ($log < 0) ? $this->internalPrecision - $log : $this->internalPrecision; // internal precision |
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for ($i = 0; $i < 2; $i++) { |
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// Determine what unit IN THIS SYSTEM we need to convert to |
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if ($dest_state === $state) { |
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// Simple conversion |
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$dest_unit = $to_unit; |
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} else { |
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// Convert to the smallest unit, pending a system shift |
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$dest_unit = self::$units[$state][$dest_state][0]; |
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} |
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// Do the conversion if necessary |
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if ($dest_unit !== $unit) { |
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$factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp); |
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$n = $this->mul($n, $factor, $cp); |
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$unit = $dest_unit; |
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} |
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// Output was zero, so bail out early. Shouldn't ever happen. |
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if ($n === '') { |
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$n = '0'; |
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$unit = $to_unit; |
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break; |
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} |
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// It was a simple conversion, so bail out |
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if ($dest_state === $state) { |
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break; |
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} |
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if ($i !== 0) { |
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// Conversion failed! Apparently, the system we forwarded |
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// to didn't have this unit. This should never happen! |
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return false; |
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} |
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// Pre-condition: $i == 0 |
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// Perform conversion to next system of units |
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$n = $this->mul($n, self::$units[$state][$dest_state][1], $cp); |
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$unit = self::$units[$state][$dest_state][2]; |
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$state = $dest_state; |
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// One more loop around to convert the unit in the new system. |
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} |
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// Post-condition: $unit == $to_unit |
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if ($unit !== $to_unit) { |
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return false; |
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} |
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// Useful for debugging: |
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//echo "<pre>n"; |
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//echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n"; |
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$n = $this->round($n, $sigfigs); |
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if (strpos($n, '.') !== false) { |
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$n = rtrim($n, '0'); |
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} |
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$n = rtrim($n, '.'); |
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return new HTMLPurifier_Length($n, $unit); |
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} |
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/** |
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* Returns the number of significant figures in a string number. |
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* @param string $n Decimal number |
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* @return int number of sigfigs |
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*/ |
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public function getSigFigs($n) |
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{ |
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$n = ltrim($n, '0+-'); |
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$dp = strpos($n, '.'); // decimal position |
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if ($dp === false) { |
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$sigfigs = strlen(rtrim($n, '0')); |
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} else { |
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$sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character |
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if ($dp !== 0) { |
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$sigfigs--; |
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} |
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} |
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return $sigfigs; |
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} |
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/** |
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* Adds two numbers, using arbitrary precision when available. |
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* @param string $s1 |
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* @param string $s2 |
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* @param int $scale |
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* @return string |
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*/ |
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private function add($s1, $s2, $scale) |
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{ |
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if ($this->bcmath) { |
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return bcadd($s1, $s2, $scale); |
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} else { |
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return $this->scale((float)$s1 + (float)$s2, $scale); |
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} |
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} |
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/** |
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* Multiples two numbers, using arbitrary precision when available. |
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* @param string $s1 |
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* @param string $s2 |
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* @param int $scale |
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* @return string |
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*/ |
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private function mul($s1, $s2, $scale) |
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{ |
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if ($this->bcmath) { |
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return bcmul($s1, $s2, $scale); |
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} else { |
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return $this->scale((float)$s1 * (float)$s2, $scale); |
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} |
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} |
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/** |
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* Divides two numbers, using arbitrary precision when available. |
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* @param string $s1 |
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* @param string $s2 |
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* @param int $scale |
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* @return string |
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*/ |
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private function div($s1, $s2, $scale) |
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{ |
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if ($this->bcmath) { |
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return bcdiv($s1, $s2, $scale); |
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} else { |
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return $this->scale((float)$s1 / (float)$s2, $scale); |
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} |
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} |
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/** |
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* Rounds a number according to the number of sigfigs it should have, |
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* using arbitrary precision when available. |
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* @param float $n |
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* @param int $sigfigs |
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* @return string |
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*/ |
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private function round($n, $sigfigs) |
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{ |
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$new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1 |
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$rp = $sigfigs - $new_log - 1; // Number of decimal places needed |
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$neg = $n < 0 ? '-' : ''; // Negative sign |
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if ($this->bcmath) { |
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if ($rp >= 0) { |
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$n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1); |
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$n = bcdiv($n, '1', $rp); |
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} else { |
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// This algorithm partially depends on the standardized |
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// form of numbers that comes out of bcmath. |
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$n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0); |
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$n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1); |
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} |
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return $n; |
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} else { |
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return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1); |
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} |
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} |
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/** |
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* Scales a float to $scale digits right of decimal point, like BCMath. |
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* @param float $r |
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* @param int $scale |
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* @return string |
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*/ |
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private function scale($r, $scale) |
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{ |
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if ($scale < 0) { |
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// The f sprintf type doesn't support negative numbers, so we |
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// need to cludge things manually. First get the string. |
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$r = sprintf('%.0f', (float)$r); |
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// Due to floating point precision loss, $r will more than likely |
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// look something like 4652999999999.9234. We grab one more digit |
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// than we need to precise from $r and then use that to round |
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// appropriately. |
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$precise = (string)round(substr($r, 0, strlen($r) + $scale), -1); |
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// Now we return it, truncating the zero that was rounded off. |
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return substr($precise, 0, -1) . str_repeat('0', -$scale + 1); |
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} |
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return sprintf('%.' . $scale . 'f', (float)$r); |
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} |
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} |
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// vim: et sw=4 sts=4 |
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