한글 초성 추출하기

<?php
function utf8_strlen($str) { return mb_strlen($str, 'UTF-8'); }
function utf8_charAt($str, $num) { return mb_substr($str, $num, 1, 'UTF-8'); }
function utf8_ord($ch) {
  $len = strlen($ch);
  if($len <= 0) return false;
  $h = ord($ch{0});
  if ($h <= 0x7F) return $h;
  if ($h < 0xC2) return false;
  if ($h <= 0xDF && $len>1) return ($h & 0x1F) <<  6 | (ord($ch{1}) & 0x3F);
  if ($h <= 0xEF && $len>2) return ($h & 0x0F) << 12 | (ord($ch{1}) & 0x3F) << 6 | (ord($ch{2}) & 0x3F);          
  if ($h <= 0xF4 && $len>3) return ($h & 0x0F) << 18 | (ord($ch{1}) & 0x3F) << 12 | (ord($ch{2}) & 0x3F) << 6 | (ord($ch{3}) & 0x3F);
  return false;
}

function cho_hangul($str) {
  $cho = array("ㄱ","ㄲ","ㄴ","ㄷ","ㄸ","ㄹ","ㅁ","ㅂ","ㅃ","ㅅ","ㅆ","ㅇ","ㅈ","ㅉ","ㅊ","ㅋ","ㅌ","ㅍ","ㅎ");
  $result = "";
  for ($i=0; $i<utf8_strlen($str); $i++) {
    $code = utf8_ord(utf8_charAt($str, $i)) - 44032;
    if ($code > -1 && $code < 11172) {
      $cho_idx = $code / 588;      
      $result .= $cho[$cho_idx];
    }
  }
  return $result;
}

echo cho_hangul("안녕하세요");