/* random3.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 N 25

#define MAX 100

/* this GPU kernel function is used to initialize the random states */
__global__ void init(unsigned int seed, curandState_t* states) {

    /* we have to initialize the state */
    curand_init(seed, /* the seed can be the same for each core, here we pass the time in from the CPU */
                blockIdx.x, /* the sequence number should be different for each core (unless you want all
                               cores to get the same sequence of numbers for some reason - use thread id! */
                0, /* the offset is how much extra we advance in the sequence for each call, can be 0 */
                &states[blockIdx.x]);
}

/* this GPU kernel takes an array of states, and an array of ints, and puts a random int into each */
__global__ void randoms(curandState_t* states, unsigned int* numbers) {
    /* curand works like rand - except that it takes a state as a parameter */
    numbers[blockIdx.x] = curand(&states[blockIdx.x]) % 100;
}

int main() {
    /* 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* states;

    /* allocate space on the GPU for the random states */
    cudaMalloc((void**) &states, N * sizeof(curandState_t));

    /* invoke the GPU to initialize all of the random states */
    init<<<N, 1>>>(time(0), states);

    /* allocate an array of unsigned ints on the CPU and GPU */
    unsigned int cpu_nums[N];
    unsigned int* gpu_nums;
    cudaMalloc((void**) &gpu_nums, N * sizeof(unsigned int));

    /* invoke the kernel to get some random numbers */
    randoms<<<N, 1>>>(states, gpu_nums);

    /* copy the random numbers back */
    cudaMemcpy(cpu_nums, gpu_nums, N * sizeof(unsigned int), cudaMemcpyDeviceToHost);

    /* print them out */
    for (int i = 0; i < N; i++) {
        printf("%u\n", cpu_nums[i]);
    }

    /* free the memory we allocated for the states and numbers */
    cudaFree(states);
    cudaFree(gpu_nums);

    return 0;
}