"unknown error" on simple RNG Probably simple, but I can't see what it is.

I’ve tried to make a random number generator (just a simple linear congruential ported from rand()), but it reports “unknown error” when initializing. It is probably a bad pointer or overflow error, and I’ve tried to fix that, but it still doesn’t work. Can anyone see what it is? Here’s the entire relevant code. I use values of _x, _y and _z as 256, 64 and 256. Thanks in advance.

__device__ unsigned long int* d_rand;

__global__ void _initRand(size_t _x, size_t _y, size_t _z,size_t slice)


	int x = blockIdx.x*blockDim.x + threadIdx.x;

	int y = blockIdx.y*blockDim.y + threadIdx.y;

	if(x>=_x || y>=_y) return;

	int sliceLoc = x+_x*y;

	for(int z = 0; z < _z; z++)


		unsigned long int i = sliceLoc+slice*z;

		d_rand[i] = (i+1)*i*i;



void initRand(size_t _x, size_t _y, size_t _z)


	cudaMalloc((void**)&d_rand, _x * _y * _z * sizeof(unsigned long int));

	int size = 16;

	dim3 blockSize(size,size);

	dim3 gridSize((_x+size-1)/size,(_y+size-1)/size);




__device__ float frand(int x, int y, int z, size_t _x, size_t _y, size_t _z)


	int i = x+_x*y+_x*_y*z;

	d_rand[i] = d_rand[i] * 1103515245 + 12345;

	float rand = (float)((d_rand[i]/65536) % 32768)/32768.0f;

	return rand;


Hi, just move device function “frand” higher than global function “_initRand”. It should work ;-)