library/HTMLPurifier/UnitConverter.php

   1 <?php
   2
   3 /**
   4  * Class for converting between different unit-lengths as specified by
   5  * CSS.
   6  */
   7 class HTMLPurifier_UnitConverter
   8 {
   9
  10     const ENGLISH = 1;
  11     const METRIC = 2;
  12     const DIGITAL = 3;
  13
  14     /**
  15      * Units information array. Units are grouped into measuring systems
  16      * (English, Metric), and are assigned an integer representing
  17      * the conversion factor between that unit and the smallest unit in
  18      * the system. Numeric indexes are actually magical constants that
  19      * encode conversion data from one system to the next, with a O(n^2)
  20      * constraint on memory (this is generally not a problem, since
  21      * the number of measuring systems is small.)
  22      */
  23     protected static $units = array(
  24         self::ENGLISH => array(
  25             'px' => 3, // This is as per CSS 2.1 and Firefox. Your mileage may vary
  26             'pt' => 4,
  27             'pc' => 48,
  28             'in' => 288,
  29             self::METRIC => array('pt', '0.352777778', 'mm'),
  30         ),
  31         self::METRIC => array(
  32             'mm' => 1,
  33             'cm' => 10,
  34             self::ENGLISH => array('mm', '2.83464567', 'pt'),
  35         ),
  36     );
  37
  38     /**
  39      * Minimum bcmath precision for output.
  40      */
  41     protected $outputPrecision;
  42
  43     /**
  44      * Bcmath precision for internal calculations.
  45      */
  46     protected $internalPrecision;
  47
  48     /**
  49      * Whether or not BCMath is available
  50      */
  51     private $bcmath;
  52
  53     public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) {
  54         $this->outputPrecision = $output_precision;
  55         $this->internalPrecision = $internal_precision;
  56         $this->bcmath = !$force_no_bcmath && function_exists('bcmul');
  57     }
  58
  59     /**
  60      * Converts a length object of one unit into another unit.
  61      * @param HTMLPurifier_Length $length
  62      *      Instance of HTMLPurifier_Length to convert. You must validate()
  63      *      it before passing it here!
  64      * @param string $to_unit
  65      *      Unit to convert to.
  66      * @note
  67      *      About precision: This conversion function pays very special
  68      *      attention to the incoming precision of values and attempts
  69      *      to maintain a number of significant figure. Results are
  70      *      fairly accurate up to nine digits. Some caveats:
  71      *          - If a number is zero-padded as a result of this significant
  72      *            figure tracking, the zeroes will be eliminated.
  73      *          - If a number contains less than four sigfigs ($outputPrecision)
  74      *            and this causes some decimals to be excluded, those
  75      *            decimals will be added on.
  76      */
  77     public function convert($length, $to_unit) {
  78
  79         if (!$length->isValid()) return false;
  80
  81         $n    = $length->getN();
  82         $unit = $length->getUnit();
  83
  84         if ($n === '0' || $unit === false) {
  85             return new HTMLPurifier_Length('0', false);
  86         }
  87
  88         $state = $dest_state = false;
  89         foreach (self::$units as $k => $x) {
  90             if (isset($x[$unit])) $state = $k;
  91             if (isset($x[$to_unit])) $dest_state = $k;
  92         }
  93         if (!$state || !$dest_state) return false;
  94
  95         // Some calculations about the initial precision of the number;
  96         // this will be useful when we need to do final rounding.
  97         $sigfigs = $this->getSigFigs($n);
  98         if ($sigfigs < $this->outputPrecision) $sigfigs = $this->outputPrecision;
  99
 100         // BCMath's internal precision deals only with decimals. Use
 101         // our default if the initial number has no decimals, or increase
 102         // it by how ever many decimals, thus, the number of guard digits
 103         // will always be greater than or equal to internalPrecision.
 104         $log = (int) floor(log(abs($n), 10));
 105         $cp = ($log < 0) ? $this->internalPrecision - $log : $this->internalPrecision; // internal precision
 106
 107         for ($i = 0; $i < 2; $i++) {
 108
 109             // Determine what unit IN THIS SYSTEM we need to convert to
 110             if ($dest_state === $state) {
 111                 // Simple conversion
 112                 $dest_unit = $to_unit;
 113             } else {
 114                 // Convert to the smallest unit, pending a system shift
 115                 $dest_unit = self::$units[$state][$dest_state][0];
 116             }
 117
 118             // Do the conversion if necessary
 119             if ($dest_unit !== $unit) {
 120                 $factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
 121                 $n = $this->mul($n, $factor, $cp);
 122                 $unit = $dest_unit;
 123             }
 124
 125             // Output was zero, so bail out early. Shouldn't ever happen.
 126             if ($n === '') {
 127                 $n = '0';
 128                 $unit = $to_unit;
 129                 break;
 130             }
 131
 132             // It was a simple conversion, so bail out
 133             if ($dest_state === $state) {
 134                 break;
 135             }
 136
 137             if ($i !== 0) {
 138                 // Conversion failed! Apparently, the system we forwarded
 139                 // to didn't have this unit. This should never happen!
 140                 return false;
 141             }
 142
 143             // Pre-condition: $i == 0
 144
 145             // Perform conversion to next system of units
 146             $n = $this->mul($n, self::$units[$state][$dest_state][1], $cp);
 147             $unit = self::$units[$state][$dest_state][2];
 148             $state = $dest_state;
 149
 150             // One more loop around to convert the unit in the new system.
 151
 152         }
 153
 154         // Post-condition: $unit == $to_unit
 155         if ($unit !== $to_unit) return false;
 156
 157         // Useful for debugging:
 158         //echo "<pre>n";
 159         //echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n";
 160
 161         $n = $this->round($n, $sigfigs);
 162         if (strpos($n, '.') !== false) $n = rtrim($n, '0');
 163         $n = rtrim($n, '.');
 164
 165         return new HTMLPurifier_Length($n, $unit);
 166     }
 167
 168     /**
 169      * Returns the number of significant figures in a string number.
 170      * @param string $n Decimal number
 171      * @return int number of sigfigs
 172      */
 173     public function getSigFigs($n) {
 174         $n = ltrim($n, '0+-');
 175         $dp = strpos($n, '.'); // decimal position
 176         if ($dp === false) {
 177             $sigfigs = strlen(rtrim($n, '0'));
 178         } else {
 179             $sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character
 180             if ($dp !== 0) $sigfigs--;
 181         }
 182         return $sigfigs;
 183     }
 184
 185     /**
 186      * Adds two numbers, using arbitrary precision when available.
 187      */
 188     private function add($s1, $s2, $scale) {
 189         if ($this->bcmath) return bcadd($s1, $s2, $scale);
 190         else return $this->scale($s1 + $s2, $scale);
 191     }
 192
 193     /**
 194      * Multiples two numbers, using arbitrary precision when available.
 195      */
 196     private function mul($s1, $s2, $scale) {
 197         if ($this->bcmath) return bcmul($s1, $s2, $scale);
 198         else return $this->scale($s1 * $s2, $scale);
 199     }
 200
 201     /**
 202      * Divides two numbers, using arbitrary precision when available.
 203      */
 204     private function div($s1, $s2, $scale) {
 205         if ($this->bcmath) return bcdiv($s1, $s2, $scale);
 206         else return $this->scale($s1 / $s2, $scale);
 207     }
 208
 209     /**
 210      * Rounds a number according to the number of sigfigs it should have,
 211      * using arbitrary precision when available.
 212      */
 213     private function round($n, $sigfigs) {
 214         $new_log = (int) floor(log(abs($n), 10)); // Number of digits left of decimal - 1
 215         $rp = $sigfigs - $new_log - 1; // Number of decimal places needed
 216         $neg = $n < 0 ? '-' : ''; // Negative sign
 217         if ($this->bcmath) {
 218             if ($rp >= 0) {
 219                 $n = bcadd($n, $neg . '0.' .  str_repeat('0', $rp) . '5', $rp + 1);
 220                 $n = bcdiv($n, '1', $rp);
 221             } else {
 222                 // This algorithm partially depends on the standardized
 223                 // form of numbers that comes out of bcmath.
 224                 $n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0);
 225                 $n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1);
 226             }
 227             return $n;
 228         } else {
 229             return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1);
 230         }
 231     }
 232
 233     /**
 234      * Scales a float to $scale digits right of decimal point, like BCMath.
 235      */
 236     private function scale($r, $scale) {
 237         if ($scale < 0) {
 238             // The f sprintf type doesn't support negative numbers, so we
 239             // need to cludge things manually. First get the string.
 240             $r = sprintf('%.0f', (float) $r);
 241             // Due to floating point precision loss, $r will more than likely
 242             // look something like 4652999999999.9234. We grab one more digit
 243             // than we need to precise from $r and then use that to round
 244             // appropriately.
 245             $precise = (string) round(substr($r, 0, strlen($r) + $scale), -1);
 246             // Now we return it, truncating the zero that was rounded off.
 247             return substr($precise, 0, -1) . str_repeat('0', -$scale + 1);
 248         }
 249         return sprintf('%.' . $scale . 'f', (float) $r);
 250     }
 251
 252 }
 253
 254 // vim: et sw=4 sts=4