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

[Mike Nolan]

On Wed, Jun 15, 2005 at 06:21:27PM -0400, William Pence wrote:
> 
> At issue is whether to reverse the recent decision to define the 'P' 
> variable-length array descriptors in FITS binary tables to be a pair of 
> 'signed 32-bit integers', and make them 'unsigned 32-bit integers' instead. 
>    The first integer gives the number of elements in the array, and the 2nd 
> integer gives the byte offset in the heap to the first element of the 
> array. The practical consequence of this change is that it will double the 
> allowed heap size from about 2.1 GB to about 4.2 GB.
> 

I would recommend *against* this change. It only gains you one bit,
and does have potential implementation issues. It's not worth it. I
routinely run into 2GB limits, and about 2/3 as often I run into 4GB
limits. The solution is the Q descriptors, which almost everybody agrees
are necessary.

> descriptors).  Forcing the descriptors to be signed 32-bit integers 
> artificially cuts in half the potential size of the heap.

I argue that a factor of only two is too small to be of general use.
-- 
Mike Nolan +1 787 878 2612 Fax: +1 787 878 1861 nolan at naic.edu
Arecibo Observatory, HC3 Box 93995, Arecibo, Puerto Rico 00612