[gmx-developers] 64bit integers

[Erik Lindahl]

Hi,

Gromacs 4.1 won't require 64 bit support, but Gromacs 5 will (we will  
have gmx_int64_t, etc.).


On Jul 10, 2009, at 6:42 PM, Roland Schulz wrote:

> Hi,
>
> which integer type should be used for integers that should be 64bit  
> if available.
>
> My current problem: ndim*ndim*4 in gmx_covar overflows for more than  
> 7723 atoms.
>
> One could use:
> - long (is only 32bit on windows)
> - long long (is always 64bit, not defined in C89)
> - size_t (is the size of pointer)
> - same typedef
>
> - One shouldn't use long, since it wouldn't solve it on windows.
> - Using "long long" is slow (in this case unimportant) and will give  
> warning when passed to snew or memcpy.
> - size_t doesn't seem very clean and will give warnings when passed  
> to printf (unless first upcasting to "unsigned long long" and then  
> using %llu).
>
> Is C89 support required?
> Is it OK to use size_t for those integers?
>
> What is the best option?

I would use size_t since that is ISO C at least. Check include/types/ 
simple.h - Berk has added some formats for printing steps, that we  
should also augment to include windows, and change so they aren't so  
step-specific.


>
> BTW: Is it OK to change save_calloc and save_realloc to size_t  
> (currently "unsigned")?

Yes, that would agree better with ISO C.

Cheers,

Erik