81ea0f8117
HTMLPurifier defangs arbitrary submitted HTML. We're using it in the OStatus plugin, but it may be valuable for other parts of the codebase (I think OEmbed might benefit, for example).
255 lines
9.0 KiB
PHP
255 lines
9.0 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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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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*/
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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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/**
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* Whether or not BCMath is available
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*/
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private $bcmath;
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public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) {
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$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 $to_unit
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* Unit to convert to.
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* @note
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* About precision: This conversion function pays very special
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* attention to the incoming precision of values and attempts
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* to maintain a number of significant figure. Results are
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* fairly accurate up to nine digits. Some caveats:
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* - If a number is zero-padded as a result of this significant
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* figure tracking, the zeroes will be eliminated.
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* - If a number contains less than four sigfigs ($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, $to_unit) {
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if (!$length->isValid()) return false;
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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])) $state = $k;
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if (isset($x[$to_unit])) $dest_state = $k;
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}
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if (!$state || !$dest_state) return false;
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// Some calculations about the initial precision of the number;
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// this will be useful when we need to do final rounding.
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$sigfigs = $this->getSigFigs($n);
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if ($sigfigs < $this->outputPrecision) $sigfigs = $this->outputPrecision;
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// BCMath's internal precision deals only with decimals. Use
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// our default if the initial number has no decimals, or increase
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// it by how ever many decimals, thus, the number of guard digits
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// will always be greater than or equal to internalPrecision.
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$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 !== $to_unit) return false;
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// Useful for debugging:
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//echo "<pre>n";
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//echo "$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) $n = rtrim($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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* 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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$n = ltrim($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) $sigfigs--;
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}
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return $sigfigs;
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}
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/**
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* Adds two numbers, using arbitrary precision when available.
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*/
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private function add($s1, $s2, $scale) {
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if ($this->bcmath) return bcadd($s1, $s2, $scale);
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else return $this->scale($s1 + $s2, $scale);
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}
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/**
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* Multiples two numbers, using arbitrary precision when available.
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*/
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private function mul($s1, $s2, $scale) {
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if ($this->bcmath) return bcmul($s1, $s2, $scale);
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else return $this->scale($s1 * $s2, $scale);
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}
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/**
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* Divides two numbers, using arbitrary precision when available.
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*/
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private function div($s1, $s2, $scale) {
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if ($this->bcmath) return bcdiv($s1, $s2, $scale);
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else return $this->scale($s1 / $s2, $scale);
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}
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/**
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* Rounds a number according to the number of sigfigs it should have,
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* using arbitrary precision when available.
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*/
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private function round($n, $sigfigs) {
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$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 $scale digits right of decimal point, like BCMath.
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*/
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private function scale($r, $scale) {
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if ($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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