/* random2.cu */

#include <unistd.h>
#include <stdio.h>

/* we need these includes for CUDA's random number stuff */
#include <curand.h>
#include <curand_kernel.h>

#define MAX 100

/* this GPU kernel function calculates a random number and stores it in the parameter */
__global__ void random(unsigned int seed, int* result) {
    /* CUDA's random number library uses curandState_t to keep track of the seed value
       we will store a random state for every thread  */
    curandState_t state;

    /* we have to initialize the state */
    curand_init(seed, /* the seed controls the sequence of random values that are produced */
            0, /* the sequence number is only important with multiple cores */
            0, /* the offset is how much extra we advance in the sequence for each call, can be 0 */
            &state);

    /* curand works like rand - except that it takes a state as a parameter */
    *result = curand(&state) % MAX;
}

int main() {
    /* allocate an int on the GPU */
    int* gpu_x;
    cudaMalloc((void**) &gpu_x, sizeof(int));

    /* invoke the GPU to initialize all of the random states */
    random<<<1, 1>>>(time(NULL), gpu_x);

    /* copy the random number back */
    int x;
    cudaMemcpy(&x, gpu_x, sizeof(int), cudaMemcpyDeviceToHost);

    printf("Random number = %d.\n", x);

    /* free the memory we allocated */
    cudaFree(gpu_x);

    return 0;
}