php 十六进制和字符串互相转换

function SingleDecToHex($dec)
{
    $tmp="";
    $dec=$dec%16;
    if($dec<10)
        return $tmp.$dec;
    $arr=array("a","b","c","d","e","f");
    return $tmp.$arr[$dec-10];
}
function SingleHexToDec($hex)
{
    $v=ord($hex);
    if(47<$v&&$v<58)
        return $v-48;
    if(96<$v&&$v<103)
        return $v-87;
}
function SetToHexString($str)
{
    if(!$str)return false;
    $tmp="";
    for($i=0;$i<strlen($str);$i++)
    {
        $ord=ord($str[$i]);
        $tmp.=SingleDecToHex(($ord-$ord%16)/16);
        $tmp.=SingleDecToHex($ord%16);
    }
    return $tmp;
}
function UnsetFromHexString($str)
{
    if(!$str)return false;
    $tmp="";
    for($i=0;$i<strlen($str);$i+=2)
    {
        $tmp.=chr(SingleHexToDec(substr($str,$i,1))*16+SingleHexToDec(substr($str,$i+1,1)));
    }
    return $tmp;
}

echo SetToHexString("hello,大家好123");
echo "";

echo UnsetFromHexString(SetToHexString("hello,大家好123"));