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      * @type int
  41      */
  42     protected $outputPrecision;
  43
  44     /**
  45      * Bcmath precision for internal calculations.
  46      * @type int
  47      */
  48     protected $internalPrecision;
  49
  50     /**
  51      * Whether or not BCMath is available.
  52      * @type bool
  53      */
  54     private $bcmath;
  55
  56     public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false)
  57     {
  58         $this->outputPrecision = $output_precision;
  59         $this->internalPrecision = $internal_precision;
  60         $this->bcmath = !$force_no_bcmath && function_exists('bcmul');
  61     }
  62
  63     /**
  64      * Converts a length object of one unit into another unit.
  65      * @param HTMLPurifier_Length $length
  66      *      Instance of HTMLPurifier_Length to convert. You must validate()
  67      *      it before passing it here!
  68      * @param string $to_unit
  69      *      Unit to convert to.
  70      * @return HTMLPurifier_Length|bool
  71      * @note
  72      *      About precision: This conversion function pays very special
  73      *      attention to the incoming precision of values and attempts
  74      *      to maintain a number of significant figure. Results are
  75      *      fairly accurate up to nine digits. Some caveats:
  76      *          - If a number is zero-padded as a result of this significant
  77      *            figure tracking, the zeroes will be eliminated.
  78      *          - If a number contains less than four sigfigs ($outputPrecision)
  79      *            and this causes some decimals to be excluded, those
  80      *            decimals will be added on.
  81      */
  82     public function convert($length, $to_unit)
  83     {
  84         if (!$length->isValid()) {
  85             return false;
  86         }
  87
  88         $n = $length->getN();
  89         $unit = $length->getUnit();
  90
  91         if ($n === '0' || $unit === false) {
  92             return new HTMLPurifier_Length('0', false);
  93         }
  94
  95         $state = $dest_state = false;
  96         foreach (self::$units as $k => $x) {
  97             if (isset($x[$unit])) {
  98                 $state = $k;
  99             }
 100             if (isset($x[$to_unit])) {
 101                 $dest_state = $k;
 102             }
 103         }
 104         if (!$state || !$dest_state) {
 105             return false;
 106         }
 107
 108         // Some calculations about the initial precision of the number;
 109         // this will be useful when we need to do final rounding.
 110         $sigfigs = $this->getSigFigs($n);
 111         if ($sigfigs < $this->outputPrecision) {
 112             $sigfigs = $this->outputPrecision;
 113         }
 114
 115         // BCMath's internal precision deals only with decimals. Use
 116         // our default if the initial number has no decimals, or increase
 117         // it by how ever many decimals, thus, the number of guard digits
 118         // will always be greater than or equal to internalPrecision.
 119         $log = (int)floor(log(abs($n), 10));
 120         $cp = ($log < 0) ? $this->internalPrecision - $log : $this->internalPrecision; // internal precision
 121
 122         for ($i = 0; $i < 2; $i++) {
 123
 124             // Determine what unit IN THIS SYSTEM we need to convert to
 125             if ($dest_state === $state) {
 126                 // Simple conversion
 127                 $dest_unit = $to_unit;
 128             } else {
 129                 // Convert to the smallest unit, pending a system shift
 130                 $dest_unit = self::$units[$state][$dest_state][0];
 131             }
 132
 133             // Do the conversion if necessary
 134             if ($dest_unit !== $unit) {
 135                 $factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
 136                 $n = $this->mul($n, $factor, $cp);
 137                 $unit = $dest_unit;
 138             }
 139
 140             // Output was zero, so bail out early. Shouldn't ever happen.
 141             if ($n === '') {
 142                 $n = '0';
 143                 $unit = $to_unit;
 144                 break;
 145             }
 146
 147             // It was a simple conversion, so bail out
 148             if ($dest_state === $state) {
 149                 break;
 150             }
 151
 152             if ($i !== 0) {
 153                 // Conversion failed! Apparently, the system we forwarded
 154                 // to didn't have this unit. This should never happen!
 155                 return false;
 156             }
 157
 158             // Pre-condition: $i == 0
 159
 160             // Perform conversion to next system of units
 161             $n = $this->mul($n, self::$units[$state][$dest_state][1], $cp);
 162             $unit = self::$units[$state][$dest_state][2];
 163             $state = $dest_state;
 164
 165             // One more loop around to convert the unit in the new system.
 166
 167         }
 168
 169         // Post-condition: $unit == $to_unit
 170         if ($unit !== $to_unit) {
 171             return false;
 172         }
 173
 174         // Useful for debugging:
 175         //echo "<pre>n";
 176         //echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n";
 177
 178         $n = $this->round($n, $sigfigs);
 179         if (strpos($n, '.') !== false) {
 180             $n = rtrim($n, '0');
 181         }
 182         $n = rtrim($n, '.');
 183
 184         return new HTMLPurifier_Length($n, $unit);
 185     }
 186
 187     /**
 188      * Returns the number of significant figures in a string number.
 189      * @param string $n Decimal number
 190      * @return int number of sigfigs
 191      */
 192     public function getSigFigs($n)
 193     {
 194         $n = ltrim($n, '0+-');
 195         $dp = strpos($n, '.'); // decimal position
 196         if ($dp === false) {
 197             $sigfigs = strlen(rtrim($n, '0'));
 198         } else {
 199             $sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character
 200             if ($dp !== 0) {
 201                 $sigfigs--;
 202             }
 203         }
 204         return $sigfigs;
 205     }
 206
 207     /**
 208      * Adds two numbers, using arbitrary precision when available.
 209      * @param string $s1
 210      * @param string $s2
 211      * @param int $scale
 212      * @return string
 213      */
 214     private function add($s1, $s2, $scale)
 215     {
 216         if ($this->bcmath) {
 217             return bcadd($s1, $s2, $scale);
 218         } else {
 219             return $this->scale((float)$s1 + (float)$s2, $scale);
 220         }
 221     }
 222
 223     /**
 224      * Multiples two numbers, using arbitrary precision when available.
 225      * @param string $s1
 226      * @param string $s2
 227      * @param int $scale
 228      * @return string
 229      */
 230     private function mul($s1, $s2, $scale)
 231     {
 232         if ($this->bcmath) {
 233             return bcmul($s1, $s2, $scale);
 234         } else {
 235             return $this->scale((float)$s1 * (float)$s2, $scale);
 236         }
 237     }
 238
 239     /**
 240      * Divides two numbers, using arbitrary precision when available.
 241      * @param string $s1
 242      * @param string $s2
 243      * @param int $scale
 244      * @return string
 245      */
 246     private function div($s1, $s2, $scale)
 247     {
 248         if ($this->bcmath) {
 249             return bcdiv($s1, $s2, $scale);
 250         } else {
 251             return $this->scale((float)$s1 / (float)$s2, $scale);
 252         }
 253     }
 254
 255     /**
 256      * Rounds a number according to the number of sigfigs it should have,
 257      * using arbitrary precision when available.
 258      * @param float $n
 259      * @param int $sigfigs
 260      * @return string
 261      */
 262     private function round($n, $sigfigs)
 263     {
 264         $new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1
 265         $rp = $sigfigs - $new_log - 1; // Number of decimal places needed
 266         $neg = $n < 0 ? '-' : ''; // Negative sign
 267         if ($this->bcmath) {
 268             if ($rp >= 0) {
 269                 $n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1);
 270                 $n = bcdiv($n, '1', $rp);
 271             } else {
 272                 // This algorithm partially depends on the standardized
 273                 // form of numbers that comes out of bcmath.
 274                 $n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0);
 275                 $n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1);
 276             }
 277             return $n;
 278         } else {
 279             return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1);
 280         }
 281     }
 282
 283     /**
 284      * Scales a float to $scale digits right of decimal point, like BCMath.
 285      * @param float $r
 286      * @param int $scale
 287      * @return string
 288      */
 289     private function scale($r, $scale)
 290     {
 291         if ($scale < 0) {
 292             // The f sprintf type doesn't support negative numbers, so we
 293             // need to cludge things manually. First get the string.
 294             $r = sprintf('%.0f', (float)$r);
 295             // Due to floating point precision loss, $r will more than likely
 296             // look something like 4652999999999.9234. We grab one more digit
 297             // than we need to precise from $r and then use that to round
 298             // appropriately.
 299             $precise = (string)round(substr($r, 0, strlen($r) + $scale), -1);
 300             // Now we return it, truncating the zero that was rounded off.
 301             return substr($precise, 0, -1) . str_repeat('0', -$scale + 1);
 302         }
 303         return sprintf('%.' . $scale . 'f', (float)$r);
 304     }
 305 }
 306
 307 // vim: et sw=4 sts=4