CUDA 代码中的恒定内存使用量

**什么是CUDA？**

c++
#include 
#include 
__constant__ float PI = 3.1415926;
__global__ void calculateArea(float* radius, float* area) {
    int tid = blockIdx.x * blockDim.x + threadIdx.x;
    area[tid] = PI * radius[tid] * radius[tid];
}
int main() {
    const int N = 10;
    float host_radius[N] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0};
    float host_area[N];
    float* device_radius;
    float* device_area;
    cudaMalloc((void**)&device_radius, N * sizeof(float));
    cudaMalloc((void**)&device_area, N * sizeof(float));
    cudaMemcpy(device_radius, host_radius, N * sizeof(float), cudaMemcpyHostToDevice);
    dim3 gridSize(1);
    dim3 blockSize(N);
    calculateArea<<>>(device_radius, device_area);
    cudaMemcpy(host_area, device_area, N * sizeof(float), cudaMemcpyDeviceToHost);
    for (int i = 0; i < N; i++) {
        printf("Radius: %.1f, Area: %.2f\n", host_radius[i], host_area[i]);
    }
    cudaFree(device_radius);
    cudaFree(device_area);
    return 0;
}