[fitsbits] FITS 'P' descriptors: signed or unsigned?

[Mark Calabretta]

On Wed 2005/06/15 18:21:27 -0400, William Pence wrote
in a message to: FITSBITS <fitsbits at nrao.edu>

>How do others feel about this issue?  Is there a clear consensus one way or 
>the other?  Should the FITS committees be explicitly asked to vote on a 
>preference?

Currently P-descriptors are effectively only 31-bit, so it should be
possible to extend them to 32-bits and beyond in whatever way seems
best.  I favour using unsigned ints since it matches the data type to
the intended usage and provides a clean progression from 32- to 64-bit
descriptors.  

Existing software that can only handle 31-bit descriptors won't
automatically understand the extended syntax.  However, the requirement
for backwards compatibility, "once FITS always FITS", refers to the
data, not the software.

Mark Calabretta
ATNF