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Diffstat (limited to 'library/HTMLPurifier/UnitConverter.php')
| -rw-r--r-- | library/HTMLPurifier/UnitConverter.php | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/library/HTMLPurifier/UnitConverter.php b/library/HTMLPurifier/UnitConverter.php new file mode 100644 index 000000000..545d42622 --- /dev/null +++ b/library/HTMLPurifier/UnitConverter.php @@ -0,0 +1,254 @@ +<?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. + */ + protected $outputPrecision; + + /** + * Bcmath precision for internal calculations. + */ + protected $internalPrecision; + + /** + * Whether or not BCMath is available + */ + 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 $to_unit + * Unit to convert to. + * @note + * About precision: This conversion function pays very special + * attention to the incoming precision of values and attempts + * to maintain a number of significant figure. Results are + * fairly accurate up to nine digits. Some caveats: + * - If a number is zero-padded as a result of this significant + * figure tracking, the zeroes will be eliminated. + * - If a number contains less than four sigfigs ($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 $sigfigs; + } + + /** + * Adds two numbers, using arbitrary precision when available. + */ + private function add($s1, $s2, $scale) { + if ($this->bcmath) return bcadd($s1, $s2, $scale); + else return $this->scale($s1 + $s2, $scale); + } + + /** + * Multiples two numbers, using arbitrary precision when available. + */ + private function mul($s1, $s2, $scale) { + if ($this->bcmath) return bcmul($s1, $s2, $scale); + else return $this->scale($s1 * $s2, $scale); + } + + /** + * Divides two numbers, using arbitrary precision when available. + */ + private function div($s1, $s2, $scale) { + if ($this->bcmath) return bcdiv($s1, $s2, $scale); + else return $this->scale($s1 / $s2, $scale); + } + + /** + * Rounds a number according to the number of sigfigs it should have, + * using arbitrary precision when available. + */ + private function round($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 $scale digits right of decimal point, like BCMath. + */ + private function scale($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 |