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   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