/**
* Encode the given string using Huffman-encoding.
*
* @param string $input Input string containing only symbols that are mapped to codes.
* @param int $bits Passed by reference, will be populated with the number of bits used to encode the input string.
* @return string Huffman-encoded string.
*/
public function encode(string $input, int &$bits = NULL) : string
{
if ($this->symbols === NULL) {
$this->symbols = $this->code->getEncoderData();
}
$encoded = '';
$offset = 7;
$byte = 0;
for ($inputLen = strlen($input), $i = 0; $i < $inputLen; $i++) {
list($code, $len) = $this->symbols[$input[$i]];
for ($j = $len - 1; $j >= 0; $j--) {
// Get next code bit and shift it into the encoded byte at the next bit offset.
$byte |= ($code >> $j & 1) << $offset--;
$bits++;
if ($offset == -1) {
$offset = 7;
$encoded .= chr($byte);
$byte = 0;
}
}
}
// Pad encoded string with "1" bits.
if ($offset < 7) {
do {
$byte |= 1 << $offset--;
} while ($offset >= 0);
$encoded .= chr($byte);
}
return $encoded;
}
