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<?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