<?php /** * Class for converting between different unit-lengths as specified by * CSS. */ class HTMLPurifier_UnitConverter { const ENGLISH = 1; const METRIC = 2; const DIGITAL = 3; /** * 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.) */ protected static $units = array( self::ENGLISH => array( 'px' => 3, // This is as per CSS 2.1 and Firefox. Your mileage may vary 'pt' => 4, 'pc' => 48, 'in' => 288, self::METRIC => array('pt', '0.352777778', 'mm'), ), self::METRIC => array( 'mm' => 1, 'cm' => 10, self::ENGLISH => array('mm', '2.83464567', 'pt'), ), ); /** * Minimum bcmath precision for output. * @type int */ protected $outputPrecision; /** * Bcmath precision for internal calculations. * @type int */ protected $internalPrecision; /** * Whether or not BCMath is available. * @type bool */ private $bcmath; public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) { $this->outputPrecision = $output_precision; $this->internalPrecision = $internal_precision; $this->bcmath = !$force_no_bcmath && function_exists('bcmul'); } /** * 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 $to_unit * Unit to convert to. * @return HTMLPurifier_Length|bool * @note * About precision: This conversion function pays very special * attention to the incoming precision of values and attempts * to maintain a number of significant figure. Results are * fairly accurate up to nine digits. Some caveats: * - If a number is zero-padded as a result of this significant * figure tracking, the zeroes will be eliminated. * - If a number contains less than four sigfigs ($outputPrecision) * and this causes some decimals to be excluded, those * decimals will be added on. */ 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); } /** * Returns the number of significant figures in a string number. * @param string $n Decimal number * @return int number of sigfigs */ public function getSigFigs($n) { $n = ltrim($n, '0+-'); $dp = strpos($n, '.'); // decimal position if ($dp === false) { $sigfigs = strlen(rtrim($n, '0')); } else { $sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character if ($dp !== 0) { $sigfigs--; } } return $sigfigs; } /** * Adds two numbers, using arbitrary precision when available. * @param string $s1 * @param string $s2 * @param int $scale * @return string */ private function add($s1, $s2, $scale) { if ($this->bcmath) { return bcadd($s1, $s2, $scale); } else { return $this->scale((float)$s1 + (float)$s2, $scale); } } /** * Multiples two numbers, using arbitrary precision when available. * @param string $s1 * @param string $s2 * @param int $scale * @return string */ private function mul($s1, $s2, $scale) { if ($this->bcmath) { return bcmul($s1, $s2, $scale); } else { return $this->scale((float)$s1 * (float)$s2, $scale); } } /** * Divides two numbers, using arbitrary precision when available. * @param string $s1 * @param string $s2 * @param int $scale * @return string */ private function div($s1, $s2, $scale) { if ($this->bcmath) { return bcdiv($s1, $s2, $scale); } else { return $this->scale((float)$s1 / (float)$s2, $scale); } } /** * Rounds a number according to the number of sigfigs it should have, * using arbitrary precision when available. * @param float $n * @param int $sigfigs * @return string */ private function round($n, $sigfigs) { $new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1 $rp = $sigfigs - $new_log - 1; // Number of decimal places needed $neg = $n < 0 ? '-' : ''; // Negative sign if ($this->bcmath) { if ($rp >= 0) { $n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1); $n = bcdiv($n, '1', $rp); } else { // This algorithm partially depends on the standardized // form of numbers that comes out of bcmath. $n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0); $n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1); } return $n; } else { return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1); } } /** * Scales a float to $scale digits right of decimal point, like BCMath. * @param float $r * @param int $scale * @return string */ private function scale($r, $scale) { if ($scale < 0) { // The f sprintf type doesn't support negative numbers, so we // need to cludge things manually. First get the string. $r = sprintf('%.0f', (float)$r); // Due to floating point precision loss, $r will more than likely // look something like 4652999999999.9234. We grab one more digit // than we need to precise from $r and then use that to round // appropriately. $precise = (string)round(substr($r, 0, strlen($r) + $scale), -1); // Now we return it, truncating the zero that was rounded off. return substr($precise, 0, -1) . str_repeat('0', -$scale + 1); } return sprintf('%.' . $scale . 'f', (float)$r); } } // vim: et sw=4 sts=4