[fitsbits] 64-bit integer comments

[Francois Ochsenbein]

About the signed/unsigned dilemna for P/Q items in binary tables,
I tend to prefer the original FITS definitions (published in 
1995A&AS..113..159C) which explicitely says "negative offsets are 
not permitted" -- which defacto limits the value of the P offset 
to 2**31-1 (the actual length of the heap might be however
larger, if the last array is a large matrix). Similarly a limitation
of the Q offset to 2**63-1 (but again the heap might be larger)
looks quite reasonable. There is no real need to introduce the 
unsigned arithmetics -- but I feel important to clearly specify that
"negative offsets are not permitted".

For the BITPIX=64, personally I didn't see any convincing argument for 
refusing it. Why forbid the usage of FITS to represent e.g. the accurate 
tick of an event on an (x,y)  grid ? 

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Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
   11, rue de l'Universite F-67000 STRASBOURG       Phone: +33-(0)390 24 24 29
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