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【PHP】一个压缩算法可以适当的用来编码

作者:freespider / 发布于2013/12/16/ 618

function encode($string) {
  $dict = array_flip(range("\0", "\xFF"));
  $dict_size = 256;
  $word = $string[0];

  $dict_count = 256;
  $bits = 8;
  $bits_max = 256;
  $return = "";
  $rest = 0;
  $rest_length = 0;

  for ($i = 1, $j = strlen($string); $i < $j; $i++) {
    $x = $string[$i];
    $y = $word . $x;
    if (isset($dict[$y])) {
      $word .= $x;
    } else {
      $rest = ($rest << $bits) + $dict[$word];
      $rest_length += $bits;
      $dict_count++;
      if ($dict_count > $bits_max) {
        $bits_max = 1 << ++$bits;
      }
      while ($rest_length > 7) {
        $rest_length -= 8;
        $return .= chr($rest >> $rest_length);
        $rest &= (1 << $rest_length) - 1;
      }
      $dict[$y] = $dict_size++;
      $word = $x;
    }
  }

  $rest = ($rest << $bits) + $dict[$word];
  $rest_length += $bits;
  $dict_count++;
  if ($dict_count > $bits_max) {
    $bits_max = 1 << ++$bits;
  }
  while ($rest_length > 0) {
    if($rest_length>7){
      $rest_length -= 8;
      $return .= chr($rest >> $rest_length);
      $rest &= (1 << $rest_length) - 1;
    }else{
      $return .= chr($rest << (8 - $rest_length));
      $rest_length = 0;
    }
  }

  return $return;
}


function decode($binary) {
  $rest = 0;
  $rest_length = 0;
  $out_count = 257;
  $bits = 9;
  $bits_max = 512;
  $dict = range("\0", "\xFF");
  $w = $binary[0];
  $return = $w;
 
  for ($i = 1, $j = strlen($binary); $i < $j; $i++) {
    $rest = ($rest << 8) + ord($binary[$i]);
    $rest_length += 8;
    if ($rest_length >= $bits) {
      $rest_length -= $bits;
      $e = $dict[$rest >> $rest_length];
      if (!isset($e)) {
        $e = $w . $w[0];
      }
      $return .= $e;
      $dict[] = $w . $e[0];
      $w = $e;     
      $rest &= (1 << $rest_length) - 1;
      if (++$out_count > $bits_max) {
        $bits_max = 1 << ++$bits;
      }
    }
  }
 
  return $return;
}



echo decode(encode(file_get_contents('http://www.baidu.com')));

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　压缩算法　

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