php bit array in integer - php

Question

I have written a wrapper class around a byte stream in order to read bit by bit from that stream (bit arrays) using this method:
public function readBits($len) {
if($len === 0) {
return 0;
}
if($this->nextbyte === null) {
//no byte has been started yet
if($len % 8 == 0) {
//don't start a byte with the cache, even number of bytes
$ret = 0;
//just return byte count not bit count
$len /= 8;
while ($len--) {
if($this->bytestream->eof()) {
//no more bytes
return false;
}
$byte = $this->bytestream->readByte();
$ret = ($ret << 8) | ord($byte);
}
return $ret;
} else {
$this->nextbyte = ord($this->bytestream->readByte());
$this->byteshift = 0;
}
}
if($len <= 8 && $this->byteshift + $len <= 8) {
//get the bitmask e.g. 00000111 for 3
$bitmask = self::$includeBitmask[$len - 1];
//can be satisfied with the remaining bits
$ret = $this->nextbyte & $bitmask;
//shift by len
$this->nextbyte >>= $len;
$this->byteshift += $len;
} else {
//read the remaining bits first
$bitsremaining = 8 - $this->byteshift;
$ret = $this->readBits($bitsremaining);
//decrease len by the amount bits remaining
$len -= $bitsremaining;
//set the internal byte cache to null
$this->nextbyte = null;
if($len > 8) {
//read entire bytes as far as possible
for ($i = intval($len / 8); $i > 0; $i--) {
if($this->bytestream->eof()) {
//no more bytes
return false;
}
$byte = $this->bytestream->readByte();
$ret = ($ret << 8) | ord($byte);
}
//reduce len to the rest of the requested number
$len = $len % 8;
}
//read a new byte to get the rest required
$newbyte = $this->readBits($len);
$ret = ($ret << $len) | $newbyte;
}
if($this->byteshift === 8) {
//delete the cached byte
$this->nextbyte = null;
}
return $ret;
}
This allows me to read bit arrays of arbitrary length off my byte stream which are returned in integers (as php has no signed integers).
The problem appears once I try to read a bit array that is bigger than 64 bits and I am assuming if I were to use the class on a 32 bit system the problem would appear with 32 bit arrays already.
The problem is that the return value is obviously to big to be held within an integer, so it topples over into a negative integer.
My question now is what would be the best way to deal with this. I can think of:
Forcing the number to be saved as a string (I am unsure if that's even possible)
Use the GMP extension (which I kinda don't want to because I think the gmp bitwise methods are probably quite a performance hit compared to the normal bitwise operators)
Is there something I missed on this or is one of the options I mentioned actually the best way to deal with this problem?
Thanks for your help in advance