[fitsbits] 64-bit integers

[Walter Jaffe]

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> To: Mark Calabretta <mcalabre at atnf.csiro.au>
> Subject: Re: [fitsbits] 64-bit integers
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> Mark Calabretta writes:
>  > I support the proposal, though with one reservation: how will cfitsio
>  > (or your favourite FITS reader) load a BITPIX=64 image onto a 32-bit
>  > computer?  Are we assuming the availability of "long long int" in C
>  > (as is gcc), INTEGER*8 (or whatever it is) in FORTRAN, and similarly
>  > in other languages?  Will coercing these values to double precision be
>  > considered acceptable if 64-bit integers are not available?
I support the proposal if anyone has an application to which 64-bit
integers are relevant.  Whether any particular computer or software
application can handle 64-bit integers (in "native" form) is mostly
irrelvant, since FITS is a transport medium, not a local internal
format.

In the early FITS days a somewhat similar situation occured with floating
point numbers.  Each machine had its own internal representation, but
FITS supports only IEEE floating point, and each local installation
had to decide what to do with it.  In the current case you have
to choose a local representation (e.g. 2 32-bit integers) and
a local arithmetic implementation (e.g. a C-function or C++ overloaded
operator) to add/multiply/compare... the local representation.

Walter