[GRASS-dev] r38992 Vect_get_num return long

Markus Metz markus.metz.giswork at googlemail.com
Mon Sep 14 14:23:28 EDT 2009

Glynn Clements wrote:
> Markus Metz wrote:
>> AFAIKT, r38992 Vect_get_num return long has no effect because the number 
>> of features (for each type) is stored as plus_t which is int. If you 
>> want to prepare the vector libs to support more than INT_MAX objects, I 
>> would suggest to use
>> plus_t Vect_get_num_primitives(const struct Map_info *, int);
>> etc and then think about what type is appropriate for plus_t.
>> I would suggest *not* to use long because long is the same like int on 
>> 32 bit (4 bytes) and the same like long long int on 64 bit (8 bytes), 
>> i.e. a vector written with 64 bit may not be readable with 32 bit which 
>> is against all the efforts to keep the vector format independent of 
>> platform/architecture/compiler. Some unsigned integer type should work, 
>> else some checks would be needed similar to what Glynn recently 
>> implemented to get an integer type of size 8 in port_init.c. E.g. use 
>> long if possible else use long long if possible else fatal error, no 
>> integer of size 8 available (or is there something else that could have 
>> a size of 8 ?).
> 	typedef long long longest;
> 	#else
> 	typedef long longest;
> 	#endif
> ?
> If you're desperate for more than 32 bits, an IEEE "double" can
> represent integers between -2^53 and 2^53 exactly, but this is likely
> to be more trouble than it's worth (you have to be careful with
> division, you can't use a double as an array index, you can't use
> shifts or bitwise operators, ...).
IMHO, we should first make sure that the vector libs support up to 
INT_MAX (2^31 - 1) features. Vector libs LFS was a first step, and 
unless there is a revolutionary new hardware concept in the near future 
with huge amounts of RAM and much higher processing speed, building 
topology for so many features will take a long long time, particularly 
in case of areas. One solution would be to increase the speed and 
decrease the memory requirements of topology building, and I think more 
brains should be put to that task before increasing the number of 
supported features, i.e. changing plus_t from a 32-bit integer type to a 
64-bit integer type.

Markus M

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