public function UTF8CharBoundary($encodedText, $maxLength)
{
$foundSplitPos = false;
$lookBack = 3;
while (!$foundSplitPos) {
$lastChunk = substr($encodedText, $maxLength - $lookBack, $lookBack);
$encodedCharPos = strpos($lastChunk, "=");
if ($encodedCharPos !== false) {
// Found start of encoded character byte within $lookBack block.
// Check the encoded byte value (the 2 chars after the '=')
$hex = substr($encodedText, $maxLength - $lookBack + $encodedCharPos + 1, 2);
$dec = hexdec($hex);
if ($dec < 128) {
// Single byte character.
// If the encoded char was found at pos 0, it will fit
// otherwise reduce maxLength to start of the encoded char
$maxLength = $encodedCharPos == 0 ? $maxLength : $maxLength - ($lookBack - $encodedCharPos);
$foundSplitPos = true;
} elseif ($dec >= 192) {
// First byte of a multi byte character
// Reduce maxLength to split at start of character
$maxLength = $maxLength - ($lookBack - $encodedCharPos);
$foundSplitPos = true;
} elseif ($dec < 192) {
// Middle byte of a multi byte character, look further back
$lookBack += 3;
}
} else {
// No encoded character found
$foundSplitPos = true;
}
}
return $maxLength;
}