def _writedata_internal(self, fileobj):
size = 0
if self.data is not None:
# Based on the system type, determine the byteorders that
# would need to be swapped to get to big-endian output
if sys.byteorder == 'little':
swap_types = ('<', '=')
else:
swap_types = ('<',)
# deal with unsigned integer 16, 32 and 64 data
if _is_pseudo_unsigned(self.data.dtype):
# Convert the unsigned array to signed
output = np.array(
self.data - _unsigned_zero(self.data.dtype),
dtype='>i%d' % self.data.dtype.itemsize)
should_swap = False
else:
output = self.data
byteorder = output.dtype.str[0]
should_swap = (byteorder in swap_types)
if not fileobj.simulateonly:
if should_swap:
output.byteswap(True)
try:
fileobj.writearray(output)
finally:
output.byteswap(True)
else:
fileobj.writearray(output)
size += output.size * output.itemsize
return size
def _calculate_datasum(self, blocking):
"""
Calculate the value for the ``DATASUM`` card in the HDU.
"""
if self._data_loaded and self.data is not None:
# We have the data to be used.
d = self.data
# First handle the special case where the data is unsigned integer
# 16, 32 or 64
if _is_pseudo_unsigned(self.data.dtype):
d = np.array(self.data - _unsigned_zero(self.data.dtype),
dtype='i%d' % self.data.dtype.itemsize)
# Check the byte order of the data. If it is little endian we
# must swap it before calculating the datasum.
if d.dtype.str[0] != '>':
byteswapped = True
d = d.byteswap(True)
d.dtype = d.dtype.newbyteorder('>')
else:
byteswapped = False
cs = self._compute_checksum(np.fromstring(d, dtype='ubyte'),
blocking=blocking)
# If the data was byteswapped in this method then return it to
# its original little-endian order.
if byteswapped and not _is_pseudo_unsigned(self.data.dtype):
d.byteswap(True)
d.dtype = d.dtype.newbyteorder('<')
return cs
else:
# This is the case where the data has not been read from the file
# yet. We can handle that in a generic manner so we do it in the
# base class. The other possibility is that there is no data at
# all. This can also be handled in a gereric manner.
return super(_ImageBaseHDU, self)._calculate_datasum(
blocking=blocking)
