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https://github.com/ezyang/htmlpurifier.git
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16fa73afa0
- Fixed another de-underscoring in the SimpleTest library git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1746 48356398-32a2-884e-a903-53898d9a118a
165 lines
6.0 KiB
PHP
165 lines
6.0 KiB
PHP
<?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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/**
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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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'pt' => 1,
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'pc' => 12,
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'in' => 72,
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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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*/
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protected $outputPrecision;
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/**
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* Bcmath precision for internal calculations.
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*/
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protected $internalPrecision;
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public function __construct($output_precision = 4, $internal_precision = 10) {
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$this->outputPrecision = $output_precision;
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$this->internalPrecision = $internal_precision;
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}
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/**
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* Converts a length object of one unit into another unit.
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* @note
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* About precision: This conversion function pays very special
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* attention to the incoming precision of values and attempts
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* to maintain a number of significant figure. Results are
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* fairly accurate up to nine digits. Some caveats:
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* - If a number is zero-padded as a result of this significant
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* figure tracking, the zeroes will be eliminated.
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* - If a number contains less than four sigfigs ($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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* - Significant digits will be ignored for quantities greater
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* than one. This is a limitation of BCMath and I don't
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* feel like coding around it.
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*/
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public function convert($length, $to_unit) {
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if ($length->n === '0' || $length->unit === false) {
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return new HTMLPurifier_Length('0', $unit);
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}
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$state = $dest = false;
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foreach (self::$units as $k => $x) {
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if (isset($x[$length->unit])) $state = $k;
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if (isset($x[$to_unit])) $dest_state = $k;
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}
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if (!$state || !$dest_state) return false;
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$n = $length->n;
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$unit = $length->unit;
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// Some calculations about the initial precision of the number;
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// this will be useful when we need to do final rounding.
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$log = (int) floor(log($n, 10));
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if (strpos($n, '.') === false) {
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$sigfigs = strlen(trim($n, '0+-'));
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} else {
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$sigfigs = strlen(ltrim($n, '0+-')) - 1; // eliminate extra decimal character
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}
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if ($sigfigs < $this->outputPrecision) $sigfigs = $this->outputPrecision;
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// BCMath's internal precision deals only with decimals. Use
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// our default if the initial number has no decimals, or increase
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// it by how ever many decimals, thus, the number of guard digits
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// will always be greater than or equal to internalPrecision.
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$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 = bcdiv(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
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$n = bcmul($n, $factor, $cp);
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$unit = $dest_unit;
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}
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// Output was zero, so bail out early
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if ($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 = bcmul($n, self::$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 !== $to_unit) return false;
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// Calculate how many decimals we need ($rp)
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// Calculations will always be carried to the decimal; this is
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// a limitation with BC (we can't set the scale to be negative)
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$new_log = (int) floor(log($n, 10));
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$rp = $sigfigs - $new_log - $log - 1;
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if ($rp < 0) $rp = 0;
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$n = bcadd($n, '0.' . str_repeat('0', $rp) . '5', $rp + 1);
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$n = bcdiv($n, '1', $rp);
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if (strpos($n, '.') !== false) $n = rtrim($n, '0');
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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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