php获取汉字拼音首字母 实现的原理是什么？

Question

function getfirstchar($s0)
{

$fchar = ord($s0{0});
if ($fchar >= ord("A") and $fchar <= ord("z"))
    return strtoupper($s0{0});
$s = iconv("UTF-8", "gb2312", $s0);
$asc = ord($s{0}) * 256 + ord($s{1}) - 65536;
if ($asc >= -20319 and $asc <= -20284)
    return "A";
if ($asc >= -20283 and $asc <= -19776)
    return "B";
if ($asc >= -19775 and $asc <= -19219)
    return "C";
if ($asc >= -19218 and $asc <= -18711)
    return "D";
if ($asc >= -18710 and $asc <= -18527)
    return "E";
if ($asc >= -18526 and $asc <= -18240)
    return "F";
if ($asc >= -18239 and $asc <= -17923)
    return "G";
if ($asc >= -17922 and $asc <= -17418)
    return "H";
if ($asc >= -17417 and $asc <= -16475)
    return "J";
if ($asc >= -16474 and $asc <= -16213)
    return "K";
if ($asc >= -16212 and $asc <= -15641)
    return "L";
if ($asc >= -15640 and $asc <= -15166)
    return "M";
if ($asc >= -15165 and $asc <= -14923)
    return "N";
if ($asc >= -14922 and $asc <= -14915)
    return "O";
if ($asc >= -14914 and $asc <= -14631)
    return "P";
if ($asc >= -14630 and $asc <= -14150)
    return "Q";
if ($asc >= -14149 and $asc <= -14091)
    return "R";
if ($asc >= -14090 and $asc <= -13319)
    return "S";
if ($asc >= -13318 and $asc <= -12839)
    return "T";
if ($asc >= -12838 and $asc <= -12557)
    return "W";
if ($asc >= -12556 and $asc <= -11848)
    return "X";
if ($asc >= -11847 and $asc <= -11056)
    return "Y";
if ($asc >= -11055 and $asc <= -10247)
    return "Z";
return null;

}

Answer 1

先转换为GB2312。GB2312共收录6763个汉字，其中按使用频度分两部分一级汉字3755个，按拼音排序，二级汉字3008个，按部首排序。
这个就是按区间分隔的，这个方法并不是很好，因为只能识别3700多个汉字。最好是用一个从全拼输入法的码表得到的转换表，反查拼音。还能处理多音字的问题。

Answer 2

原理就是查字典