dolphin/single-functions/is-utf-8.php

<?php
/**
 *  dolphin. Collection of useful PHP skeletons.
 *  Copyright (C) 2019  Johannes 'Banana' Keßler
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the COMMON DEVELOPMENT AND DISTRIBUTION LICENSE
 *
 * You should have received a copy of the
 * COMMON DEVELOPMENT AND DISTRIBUTION LICENSE (CDDL) Version 1.0
 * along with this program.  If not, see http://www.sun.com/cddl/cddl.html
 */

/**
 * return if the given string is utf8
 * http://php.net/manual/en/function.mb-detect-encoding.php
 *
 * @param string $string
 * @return number
 */
function is_utf8($string) {
   return preg_match('%^(?:
         [\x09\x0A\x0D\x20-\x7E]            # ASCII
       | [\xC2-\xDF][\x80-\xBF]             # non-overlong 2-byte
       |  \xE0[\xA0-\xBF][\x80-\xBF]        # excluding overlongs
       | [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}  # straight 3-byte
       |  \xED[\x80-\x9F][\x80-\xBF]        # excluding surrogates
       |  \xF0[\x90-\xBF][\x80-\xBF]{2}     # planes 1-3
       | [\xF1-\xF3][\x80-\xBF]{3}          # planes 4-15
       |  \xF4[\x80-\x8F][\x80-\xBF]{2}     # plane 16
   )*$%xs', $string);
}

?>