[GRASS-dev] vector large file support

[Glynn Clements]

Markus Metz wrote:

> >> I got confused by this endian-ness and confused low/high word with 
> >> first/second word. With the current code, the low word would be the 
> >> second word when doing 2 32bit reads on a 64bit sized buffer, 
> >> independent on a endian-ness mismatch. In this case, the libs would have 
> >> to check if the high word is != 0 and then exit with an ERROR message, 
> >> right?
> >>     
> >
> > Right. The files are always written big-endian, so the high word will
> > always be first in the file.
> 
> I'm not so sure about that, why is byte order stored in the topo header? 
> Byte order for writing out is determined just before writing topo/cidx.

Okay; maybe that's just the internal default. I'm looking at
dig_init_portable(), which copies the *_cnvrt arrays for big-endian
and reverses them for little-endian.

I don't know why that code needs to be so obtuse.

> > As well as checking that the high word is zero, you also need to check
> > that the low word is <= 0x7fffffff (off_t is signed, hence the limit
> > being 2GiB not 4GiB).
> 
> OK. Additionally the whole thing should not be negative, that would be 
> an invalid offset.

I'm assuming that the individual words are treated as unsigned.

-- 
Glynn Clements <glynn at gclements.plus.com>