PHPで漢字を数字に変換する方法

function checkNatInt($str) {
  $map = array(
    '一' => '1','二' => '2','三' => '3','四' => '4','五' => '5','六' => '6','七' => '7','八' => '8','九' => '9',
    '壹' => '1','贰' => '2','叁' => '3','肆' => '4','伍' => '5','陆' => '6','柒' => '7','捌' => '8','玖' => '9',
    '零' => '0','两' => '2',
    '仟' => '千','佰' => '百','拾' => '十',
    '万万' => '亿',
  ); 
  
  $str = str_replace(array_keys($map), array_values($map), $str);
  $str = checkString($str, '/([\d亿万千百十]+)/u');
  
  $func_c2i = function ($str, $plus = false) use(&$func_c2i) {
    if(false === $plus) {
      $plus = array('亿' => 100000000,'万' => 10000,'千' => 1000,'百' => 100,'十' => 10,);
    }  
  
    $i = 0;
    if($plus)
    foreach($plus as $k => $v) {
      $i++;
      if(strpos($str, $k) !== false) {
        $ex = explode($k, $str, 2); 
        $new_plus = array_slice($plus, $i, null, true);
        $l = $func_c2i($ex[0], $new_plus);
        $r = $func_c2i($ex[1], $new_plus);
        if($l == 0) $l = 1;
        return $l * $v + $r;
      }
    }
  
    return (int)$str;
  }
  return $func_c2i($str);
 }
  
 //来自uct php微信开发框架，其中的checkString函数如下
 function checkString($var, $check = '', $default = '') {
  if (!is_string($var)) {
    if(is_numeric($var)) {
      $var = (string)$var;
    }
    else {
      return $default;
    }
  }
  if ($check) {
     return (preg_match($check, $var, $ret) ? $ret[1] : $default);
  }
  
  return $var;
}