Decompress byte string to array of integers of any bit size <= 32.

    Parameters
    ----------
    data : byte str
        Data to decompress.
    dtype : numpy.dtype or str
        A numpy boolean or integer type.
    itemsize : int
        Number of bits per integer.
    runlen : int
        Number of consecutive integers, after which to start at next byte.

def unpackints(data, dtype, itemsize, runlen=0):
    """Decompress byte string to array of integers of any bit size <= 32.

    Parameters
    ----------
    data : byte str
        Data to decompress.
    dtype : numpy.dtype or str
        A numpy boolean or integer type.
    itemsize : int
        Number of bits per integer.
    runlen : int
        Number of consecutive integers, after which to start at next byte.

    """
    if itemsize == 1:  # bitarray
        data = numpy.fromstring(data, '|B')
        data = numpy.unpackbits(data)
        if runlen % 8:
            data = data.reshape(-1, runlen+(8-runlen%8))
            data = data[:, :runlen].reshape(-1)
        return data.astype(dtype)

    dtype = numpy.dtype(dtype)
    if itemsize in (8, 16, 32, 64):
        return numpy.fromstring(data, dtype)
    if itemsize < 1 or itemsize > 32:
        raise ValueError("itemsize out of range: %i" % itemsize)
    if dtype.kind not in "biu":
        raise ValueError("invalid dtype")

    itembytes = next(i for i in (1, 2, 4, 8) if 8 * i >= itemsize)
    if itembytes != dtype.itemsize:
        raise ValueError("dtype.itemsize too small")
    if runlen == 0:
        runlen = len(data) // itembytes
    skipbits = runlen*itemsize % 8
    if skipbits:
        skipbits = 8 - skipbits
    shrbits = itembytes*8 - itemsize
    bitmask = int(itemsize*'1'+'0'*shrbits, 2)
    dtypestr = '>' + dtype.char  # dtype always big endian?

    unpack = struct.unpack
    l = runlen * (len(data)*8 // (runlen*itemsize + skipbits))
    result = numpy.empty((l, ), dtype)
    bitcount = 0
    for i in range(len(result)):
        start = bitcount // 8
        s = data[start:start+itembytes]
        try:
            code = unpack(dtypestr, s)[0]
        except Exception:
            code = unpack(dtypestr, s + b'\x00'*(itembytes-len(s)))[0]
        code = code << (bitcount % 8)
        code = code & bitmask
        result[i] = code >> shrbits
        bitcount += itemsize
        if (i+1) % runlen == 0:
            bitcount += skipbits
    return result