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# Source code for fabio.readbytestream

    """
    Reads a bytestream

    Authors: Jon Wright    Henning O. Sorensen & Erik Knudsen
             ESRF          Risoe National Laboratory
    """

    import numpy, logging
    logger = logging.getLogger("readbytestream")
    DATATYPES = {
        # type  sign bytes
        ("int", 'n', 1) : numpy.uint8,
        ("int", 'n', 2) : numpy.uint16,
        ("int", 'n', 4) : numpy.uint32,
        ("int", 'y', 1) : numpy.int8,
        ("int", 'y', 2) : numpy.int16,
        ("int", 'y', 4) : numpy.int32,
        ('float', 'y', 4) : numpy.float32, # does this occur in bruker?
        ('double', 'y', 4): numpy.float64
        }

    def readbytestream(fil,
                       offset,
                       x,
                       y,
                       nbytespp,
                       datatype='int',
                       signed='n',
                       swap='n',
                       typeout=numpy.uint16):
        """
        Reads in a bytestream from a file (which may be a string indicating
        a filename, or an already opened file (should be "rb"))
        offset is the position (in bytes) where the pixel data start
        nbytespp = number of bytes per pixel
        type can be int or float (4 bytes pp) or double (8 bytes pp)
        signed: normally signed data 'y', but 'n' to try to get back the
        right numbers when unsigned data are converted to signed
        (python once had no unsigned numeric types.)
        swap, normally do not bother, but 'y' to swap bytes
        typeout is the numpy type to output, normally uint16,
        but more if overflows occurred
        x and y are the pixel dimensions

        TODO : Read in regions of interest

        PLEASE LEAVE THE STRANGE INTERFACE ALONE -
        IT IS USEFUL FOR THE BRUKER FORMAT
        """
        tin = "dunno"
        length = nbytespp * x * y # bytes per pixel times number of pixels
        if datatype in ['float', 'double']:
            signed = 'y'

        key = (datatype, signed, nbytespp)
        try:
            tin = DATATYPES[key]
        except:
            logging.warning("datatype,signed,nbytespp " + str(key))
            raise Exception("Unknown combination of types to readbytestream")

        # Did we get a string (filename) or a readable stream object?
        if hasattr(fil, "read") and hasattr(fil, "seek"):
            infile = fil
            opened = False
        else:
            infile = open(fil, 'rb')
            opened = True

        infile.seek(offset)

        arr = numpy.array(numpy.reshape(
                numpy.fromstring(
                    infile.read(length), tin) , (x, y)), typeout)

        if swap == 'y':
            arr = arr.byteswap()

        if opened:
            infile.close()

        return arr

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