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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.

* @type int

protected $outputPrecision;

/**

* Bcmath precision for internal calculations.

* @type int

protected $internalPrecision;

/**

* Whether or not BCMath is available.

* @type bool

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.

* @return HTMLPurifier_Length|bool

* @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.

* @param string $s1

* @param string $s2

* @param int $scale

* @return string

private function add($s1, $s2, $scale)

{

if ($this->bcmath) {

return bcadd($s1, $s2, $scale);

} else {

return $this->scale((float)$s1 + (float)$s2, $scale);

}

/**

* Multiples two numbers, using arbitrary precision when available.

* @param string $s1

* @param string $s2

* @param int $scale

* @return string

private function mul($s1, $s2, $scale)

{

if ($this->bcmath) {

return bcmul($s1, $s2, $scale);

} else {

return $this->scale((float)$s1 * (float)$s2, $scale);

}

/**

* Divides two numbers, using arbitrary precision when available.

* @param string $s1

* @param string $s2

* @param int $scale

* @return string

private function div($s1, $s2, $scale)

{

if ($this->bcmath) {

return bcdiv($s1, $s2, $scale);

} else {

return $this->scale((float)$s1 / (float)$s2, $scale);

}

/**

* Rounds a number according to the number of sigfigs it should have,

* using arbitrary precision when available.

* @param float $n

* @param int $sigfigs

* @return string

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.

* @param float $r

* @param int $scale

* @return string

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

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