opencl dealing with unsigned long long integers


Please, can someone provides me help, is it possible to define a :

global_item_size = (1ULL << 56)

(in other terms: 2 exponant 56) ?

I need such amount if “work items” to execute an exhaustive attack (cryptography area).

Thank you in advance.


The opencl specification is the place where answers to such questions are best found.

e.g. see section 6.1.1 “Built-in Scalar Data Types”

work sizes are size_t, matches the device address bits - i.e. 64-bits only on64-bit devices. My GTX 480 device is only 32-bits, so 2^56 would not be possible (and i presume it would be the same for all gpu cards).

For such a problem size you probably would just run loops within each workgroup instead of leaving it to the hardware only.

Hi Notzed,

Thank you for your quick reply !

In fact, I queried the device, silimar to yours (NVIDIA GTX 470) and it returned me this :