[GRASS-dev] vector large file support

[Markus Metz]

Glynn Clements wrote:
> I have added G_fseek() and G_ftell() to 7.0 in r35818.
>   
:-)
>   
>> 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.
> 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.
>
> The issue is whether the coor file size is known at the point that you
> start writing the topo/cidx files. If the files are generated
> concurrently, then it isn't feasible. If the coor file is generated
> first, then it is.
>   
You're right, the coor file is generated first. Since we will have a 
flexible off_t size for the topo and cidx file, we can set it just 
before writing out these files.