memfrob implementation in cuda

memfrob.cu

#include <cuda_runtime.h>

__global__ void frobnicator(unsigned char *dev, int n) {
    int tid = blockIdx.x * blockDim.x + threadIdx.x;
    if (tid < n)
        dev[tid] ^= 42;
}

void *cuda_memfrob(void *mem, size_t n)
{
    unsigned char *dev;
    cudaMalloc(&dev, n);
    cudaMemcpy(dev, mem, n, cudaMemcpyHostToDevice);

    int threads = 256;
    int blocks  = (n + threads - 1) / threads;
    frobnicator<<<blocks, threads>>>(dev, n);

    cudaDeviceSynchronize();
    cudaMemcpy(mem, dev, n, cudaMemcpyDeviceToHost);
    cudaFree(dev);
    return mem;
}

#include <iostream>
int main() {
    char x[] = "CAPPUCCINO\0";
    char y[] = "CAPPUCCINO\0";
    cuda_memfrob(x, sizeof(x));
    memfrob(y, sizeof(y));

    for (int i = 0; i < sizeof(x); i++) {
        if (x[i] != y[i])
            puts("MISMATCH");
    }

    printf("CUDA: %.*s\n", sizeof(x), x);
    printf("CPU: %.*s\n", sizeof(y), y);
    return 0;
}