Instead of string_match use these two functions below


static public function string_compare($str_a, $str_b)
{
    $length = strlen($str_a);
    $length_b = strlen($str_b);

    $i = 0;
    $segmentcount = 0;
    $segmentsinfo = array();
    $segment = '';
    while ($i < $length)
    {
        $char = substr($str_a, $i, 1);
        if (strpos($str_b, $char) !== FALSE)
        {
            $segment = $segment.$char;
            if (strpos($str_b, $segment) !== FALSE)
            {
                $segmentpos_a = $i - strlen($segment) + 1;
                $segmentpos_b = strpos($str_b, $segment);
                $positiondiff = abs($segmentpos_a - $segmentpos_b);
                $posfactor = ($length - $positiondiff) / $length_b; // <-- ?
                $lengthfactor = strlen($segment)/$length;
                $segmentsinfo[$segmentcount] = array( 'segment' => $segment, 'score' => ($posfactor * $lengthfactor));
            }
            else
            {
                $segment = '';
                $i--;
                $segmentcount++;
            }
        }
        else
        {
            $segment = '';
            $segmentcount++;
        }
        $i++;
    }

    // PHP 5.3 lambda in array_map
    $totalscore = array_sum(array_map(function($v) { return $v['score'];  }, $segmentsinfo));
    return $totalscore;
}








class StringCompareJaroWinkler
{
    public function compare($str1, $str2)
    {
        return $this->JaroWinkler($str1, $str2, $PREFIXSCALE = 0.1 );
    }

    private function getCommonCharacters( $string1, $string2, $allowedDistance ){

      $str1_len = mb_strlen($string1);
      $str2_len = mb_strlen($string2);
      $temp_string2 = $string2;

      $commonCharacters='';
      for( $i=0; $i < $str1_len; $i++){

        $noMatch = True;
        // compare if char does match inside given allowedDistance
        // and if it does add it to commonCharacters
        for( $j= max( 0, $i-$allowedDistance ); $noMatch && $j < min( $i + $allowedDistance + 1, $str2_len ); $j++){
          if( $temp_string2[$j] == $string1[$i] ){
            $noMatch = False;
        $commonCharacters .= $string1[$i];
        $temp_string2[$j] = '';
          }
        }
      }
      return $commonCharacters;
    }

    private function Jaro( $string1, $string2 ){

      $str1_len = mb_strlen( $string1 );
      $str2_len = mb_strlen( $string2 );

      // theoretical distance
      $distance = (int) floor(min( $str1_len, $str2_len ) / 2.0);

      // get common characters
      $commons1 = $this->getCommonCharacters( $string1, $string2, $distance );
      $commons2 = $this->getCommonCharacters( $string2, $string1, $distance );

      if( ($commons1_len = mb_strlen( $commons1 )) == 0) return 0;
      if( ($commons2_len = mb_strlen( $commons2 )) == 0) return 0;
      // calculate transpositions
      $transpositions = 0;
      $upperBound = min( $commons1_len, $commons2_len );
      for( $i = 0; $i < $upperBound; $i++){
        if( $commons1[$i] != $commons2[$i] ) $transpositions++;
      }
      $transpositions /= 2.0;
      // return the Jaro distance
      return ($commons1_len/($str1_len) + $commons2_len/($str2_len) + ($commons1_len - $transpositions)/($commons1_len)) / 3.0;

    }

    private function getPrefixLength( $string1, $string2, $MINPREFIXLENGTH = 4 ){

      $n = min( array( $MINPREFIXLENGTH, mb_strlen($string1), mb_strlen($string2) ) );

      for($i = 0; $i < $n; $i++){
        if( $string1[$i] != $string2[$i] ){
          // return index of first occurrence of different characters
          return $i;
        }
      }
      // first n characters are the same
      return $n;
    }

    private function JaroWinkler($string1, $string2, $PREFIXSCALE = 0.1 ){

      $JaroDistance = $this->Jaro( $string1, $string2 );
      $prefixLength = $this->getPrefixLength( $string1, $string2 );
      return $JaroDistance + $prefixLength * $PREFIXSCALE * (1.0 - $JaroDistance);
    }
}

$jw = new StringCompareJaroWinkler();
echo $jw->compare("jonas","asjon");