254 lines
9 KiB
PHP
254 lines
9 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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