Markov chain generators source code, and their effectiveness

function markov($content, $gran = 5, $num = 200, $letters_line = 65) {
  $combo = $content;
  $output = "";
  $combo = preg_replace('/\s\s+/', ' ', $combo);
  $combo = preg_replace('/\n|\r/', '', $combo);
  $combo = strip_tags($combo);
  $combo = htmlspecialchars($combo);
  $combo = explode(".",$combo);
  shuffle($combo);
  $combo = implode(".", $combo);
  $textwords = explode(" ", $combo);
  $loopmax = count($textwords) - ($gran - 2) - 1;
  $frequency_table = array();
  for ($j = 0; $j < $loopmax; $j++) {
    $key_string = " ";
    $end = $j + $gran;
    for ($k = $j; $k < $end; $k++) {
      $key_string .= $textwords[$k].' ';
    }
    $frequency_table[$key_string] = ' ';
    $frequency_table[$key_string] .= $textwords[$j + $gran]." ";
    if (($j+$gran) > $loopmax ) {
      break;
    }
  }
  $buffer = "";
  $lastwords = array();
  for ($i = 0; $i < $gran; $i++) {
    $lastwords[] = $textwords[$i];
    $buffer .= " ".$textwords[$i];
  }
  for ($i = 0; $i < $num; $i++) {
    $key_string = " ";
    for ($j = 0; $j < $gran; $j++) {
      $key_string .= $lastwords[$j]." ";
    }
    if (isset($frequency_table[$key_string])) {
      $possible = explode(" ", trim($frequency_table[$key_string]));
      mt_srand();
      $c = count($possible);
      $r = mt_rand(1, $c) - 1;
      $nextword = $possible[$r];
      $buffer .= " $nextword";
      if (strlen($buffer) >= $letters_line) {
        $output .= $buffer;
        $buffer = " ";
      }
      for ($l = 0; $l < $gran - 1; $l++) {
        $lastwords[$l] = $lastwords[$l + 1];
      }
      $lastwords[$gran - 1] = $nextword;
    } 
    else {
      $lastwords = array_splice($lastwords, 0, count($lastwords));
      for ($l = 0; $l < $gran; $l++) {
        $lastwords[] = $textwords[$l];
        $buffer .= ' '.$textwords[$l];
      }
    }
  }
  $output = trim($output);
  return $output;
}

function generate_markov_table($text, $look_forward) {
    $table = array();
    
    // now walk through the text and make the index table
    for ($i = 0; $i < strlen($text); $i++) {
        $char = substr($text, $i, $look_forward);
        if (!isset($table[$char])) $table[$char] = array();
    }              
    
    // walk the array again and count the numbers
    for ($i = 0; $i < (strlen($text) - $look_forward); $i++) {
        $char_index = substr($text, $i, $look_forward);
        $char_count = substr($text, $i+$look_forward, $look_forward);
        
        if (isset($table[$char_index][$char_count])) {
            $table[$char_index][$char_count]++;
        } else {
            $table[$char_index][$char_count] = 1;
        }                
    } 

    return $table;
}

function generate_markov_text($length, $table, $look_forward) {
    // get first character
    $char = array_rand($table);
    $o = $char;

    for ($i = 0; $i < ($length / $look_forward); $i++) {
        $newchar = return_weighted_char($table[$char]);            
        
        if ($newchar) {
            $char = $newchar;
            $o .= $newchar;
        } else {       
            $char = array_rand($table);
        }
    }
    
    return $o;
}
    

function return_weighted_char($array) {
    if (!$array) return false;
    
    $total = array_sum($array);
    $rand  = mt_rand(1, $total);
    foreach ($array as $item => $weight) {
        if ($rand <= $weight) return $item;
        $rand -= $weight;
    }
}

echo markov($text, 5, 200);

$order = 5;
echo generate_markov_text(1000, generate_markov_table($text, $order), $order);