protected function decodeGeneric(string $input, int $bits) : string
{
if ($this->symbol === NULL) {
list($this->symbol, $this->codes, $this->codeLengths, $this->first, $this->steps) = $this->code->getDecoderData();
$this->stepCount = count($this->steps);
}
$len = strlen($input);
$decoded = '';
$buffer = NULL;
$byteOffset = 0;
$bitOffset = 7;
while (true) {
$code = 0;
$codeLen = 0;
// Increment in steps to avoid checking codes with a length that is not used by Huffman codes.
for ($step = 0; $step < $this->stepCount; $step++) {
for ($i = 0; $i < $this->steps[$step]; $i++) {
if ($bits-- == 0) {
break;
}
if ($buffer === NULL) {
if ($byteOffset == $len) {
if ($code === 0 || $this->isHuffmanPaddingCode($code)) {
return $decoded;
}
throw new \RuntimeException('Cannot read beyond end of Huffman-encoded string');
}
$buffer = ord($input[$byteOffset]);
}
// Read next bit and and append it as LSB (least significant bit) to the code.
$code = $code << 1 | $buffer >> $bitOffset-- & 1;
$codeLen++;
if ($bitOffset == -1) {
$byteOffset++;
$bitOffset = 7;
$buffer = NULL;
}
}
// Match code against all codes with the same length.
for ($i = 0; $i < $this->codeLengths[$codeLen]; $i++) {
if ($this->codes[$this->first[$codeLen] + $i] == $code) {
$decoded .= $this->symbol[sprintf('%0' . $codeLen . 'b', $code)];
if ($bits == 0) {
return $decoded;
}
continue 3;
}
}
if ($bits == 0) {
if ($codeLen == 0) {
return $decoded;
}
break;
}
}
if ($this->isHuffmanPaddingCode($code)) {
return $decoded;
}
break;
}
throw new \RuntimeException('Invalid Huffman code detected');
}
