Lab3. 2

#include "cuda_runtime.h"
#include "device_launch_parameters.h"
#include <cuda.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctime>
#include <clocale>
#include <cmath>

#define NUM_BLOCK 256
#define NUM_THREAD 256

const double PI = 3.14159265358979323846;

__global__ void calc(double *res, double step, int blocks, int threads, int size)
{
    for(int idx = blockIdx.x * blockDim.x + threadIdx.x;
        idx <= size;
        idx += blocks * threads)
    {
        double x = step * idx;
        res[idx] += sqrt(1 - x * x);
    }
}

int main()
{
    const int N = NUM_BLOCK * NUM_THREAD;
    double pi = 0;
    double *res, *dev_res;
    double step = 1.0 / N;
    size_t size = N * sizeof(double);
    res = (double*)malloc(size);
    cudaMalloc((void**)&dev_res, size);

    calc <<<NUM_BLOCK, NUM_THREAD>>> (dev_res, step, NUM_BLOCK, NUM_THREAD, N);
    cudaMemcpy(res, dev_res, size, cudaMemcpyDeviceToHost);

    for (int i = 0; i < N; i++)
        pi += res[i];
    pi *= 4 * step;
    pi /= N;

    printf("%d blocks, %d threads\n", NUM_BLOCK, NUM_THREAD);
    printf("Defined PI    = %.20f\n", PI);
    printf("Calculated PI = %.20f\n", pi);
    printf("Error         = %.20f\n", abs(pi - PI));

    cudaFree(dev_res);
    return 0;
}