A noob need help

[Pimbolie1979]

A noob need help

global void square_array(float *a, int N)
{
int idx = blockIdx.x * blockDim.x + threadIdx.x;
if (idx<N) a[idx] = a[idx] * a[idx];
}

square_array <<< 3, 4 >>> (a_d, N);

I need help for this code segment:

int idx = blockIdx.x * blockDim.x + threadIdx.x;
if (idx<N) a[idx] = a[idx] * a[idx];

N = 10

Can you explain the two codelines for me.

[AndyL]

int idx = blockIdx.x * blockDim.x + threadIdx.x;

This line is defining the thread’s position within the grid. It is used to access memory in vector format as shown in the next line:

if (idx<N) a[idx] = a[idx] * a[idx];

As the grid consists of 12 threads, and you only want to consider the first 10, a conditional statement is used based on the thread’s position within the grid.

Hope that makes sense…