Check if string has any big5 character in PHP

hasBig5.php

<?php
function isBig5Char ($char) {
    if (strlen($char) < 2)
        return false;

    $byte1hex = dechex(ord($char[0]));
    $byte2hex = dechex(ord($char[1]));
    $number = hexdec($byte1hex . $byte2hex);
    return (
        0x8140 <= $number &&
        $number <= 0xFEFE
    );
}

function hasBig5 ($str) {
    if (strlen($str) < 2)
        return false;

    for ($i = 0; $i < (strlen($str) - 1); $i++) {
        if (isBig5Char(substr($str, $i, 2))) {
            return true;
        }
    }

    return false;
}

$text = '寶';
$big5_text = iconv("UTF-8", "BIG5//IGNORE", $text);
if (hasBig5($big5_text)) {
    echo 'yes';
} else {
    echo 'no';
}