HTMLPurifier_UnitConverter Class Reference

Class for converting between different unit-lengths as specified by CSS. More...

Collaboration diagram for HTMLPurifier_UnitConverter:

Public Member Functions
	__construct ($output_precision=4, $internal_precision=10, $force_no_bcmath=false)
	convert ($length, $to_unit)
	Converts a length object of one unit into another unit. More...
	getSigFigs ($n)
	Returns the number of significant figures in a string number. More...

Data Fields
const	ENGLISH = 1
const	METRIC = 2
const	DIGITAL = 3

Protected Attributes
	$outputPrecision
	Minimum bcmath precision for output. More...
	$internalPrecision
	Bcmath precision for internal calculations. More...

Static Protected Attributes
static	$units
	Units information array. More...

Private Member Functions
	add ($s1, $s2, $scale)
	Adds two numbers, using arbitrary precision when available. More...
	mul ($s1, $s2, $scale)
	Multiples two numbers, using arbitrary precision when available. More...
	div ($s1, $s2, $scale)
	Divides two numbers, using arbitrary precision when available. More...
	round ($n, $sigfigs)
	Rounds a number according to the number of sigfigs it should have, using arbitrary precision when available. More...
	scale ($r, $scale)
	Scales a float to $scale digits right of decimal point, like BCMath. More...

Private Attributes
	$bcmath
	Whether or not BCMath is available. More...

Detailed Description

Class for converting between different unit-lengths as specified by CSS.

Definition at line 7 of file UnitConverter.php.

Constructor & Destructor Documentation

__construct()

HTMLPurifier_UnitConverter::__construct	(		$output_precision = 4,
			$internal_precision = 10,
			$force_no_bcmath = false
	)

Definition at line 53 of file UnitConverter.php.

                                                                                                           {
        $this->outputPrecision = $output_precision;
        $this->internalPrecision = $internal_precision;
        $this->bcmath = !$force_no_bcmath && function_exists('bcmul');
    }

Member Function Documentation

add()

HTMLPurifier_UnitConverter::add (   $s1,   $s2,   $scale  )

private

Adds two numbers, using arbitrary precision when available.

Definition at line 188 of file UnitConverter.php.

References scale().

                                           {
        if ($this->bcmath) return bcadd($s1, $s2, $scale);
        else return $this->scale($s1 + $s2, $scale);
    }

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convert()

HTMLPurifier_UnitConverter::convert	(		$length,
			$to_unit
	)

Converts a length object of one unit into another unit.

Parameters

HTMLPurifier_Length	$length	Instance of HTMLPurifier_Length to convert. You must validate() it before passing it here!
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.

Definition at line 77 of file UnitConverter.php.

References $log, $n, $outputPrecision, div(), getSigFigs(), mul(), and round().

                                               {

        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);
    }

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div()

HTMLPurifier_UnitConverter::div (   $s1,   $s2,   $scale  )

private

Divides two numbers, using arbitrary precision when available.

Definition at line 204 of file UnitConverter.php.

References scale().

Referenced by convert().

                                           {
        if ($this->bcmath) return bcdiv($s1, $s2, $scale);
        else return $this->scale($s1 / $s2, $scale);
    }

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getSigFigs()

HTMLPurifier_UnitConverter::getSigFigs

(

$n

)

Returns the number of significant figures in a string number.

Parameters

string

$n

Decimal number

Returns

int number of sigfigs

Definition at line 173 of file UnitConverter.php.

References $n.

Referenced by convert().

                                   {
        $n = ltrim($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;
    }

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mul()

HTMLPurifier_UnitConverter::mul (   $s1,   $s2,   $scale  )

private

Multiples two numbers, using arbitrary precision when available.

Definition at line 196 of file UnitConverter.php.

References scale().

Referenced by convert().

                                           {
        if ($this->bcmath) return bcmul($s1, $s2, $scale);
        else return $this->scale($s1 * $s2, $scale);
    }

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round()

HTMLPurifier_UnitConverter::round (   $n,   $sigfigs  )

private

Rounds a number according to the number of sigfigs it should have, using arbitrary precision when available.

Definition at line 213 of file UnitConverter.php.

References $n, and scale().

Referenced by convert(), and scale().

                                         {
        $new_log = (int) floor(log(abs($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);
        }
    }

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scale()

HTMLPurifier_UnitConverter::scale (   $r,   $scale  )

private

Scales a float to $scale digits right of decimal point, like BCMath.

Definition at line 236 of file UnitConverter.php.

References $r, and round().

Referenced by add(), div(), mul(), and round().

                                       {
        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);
    }

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Field Documentation

$bcmath

HTMLPurifier_UnitConverter::$bcmath

private

Whether or not BCMath is available.

Definition at line 51 of file UnitConverter.php.

$internalPrecision

HTMLPurifier_UnitConverter::$internalPrecision

protected

Bcmath precision for internal calculations.

Definition at line 46 of file UnitConverter.php.

$outputPrecision

HTMLPurifier_UnitConverter::$outputPrecision

protected

Minimum bcmath precision for output.

Definition at line 41 of file UnitConverter.php.

Referenced by convert().

$units

HTMLPurifier_UnitConverter::$units

staticprotected

Initial value:

= array(
        self::ENGLISH => array(
            'px' => 3, 
            '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'),
        ),
    )

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.)

Definition at line 23 of file UnitConverter.php.

DIGITAL

const HTMLPurifier_UnitConverter::DIGITAL = 3

Definition at line 12 of file UnitConverter.php.

ENGLISH

const HTMLPurifier_UnitConverter::ENGLISH = 1

Definition at line 10 of file UnitConverter.php.

METRIC

const HTMLPurifier_UnitConverter::METRIC = 2

Definition at line 11 of file UnitConverter.php.

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The documentation for this class was generated from the following file:

• Services/Html/HtmlPurifier/library/HTMLPurifier/UnitConverter.php