#version 450

// This variable is set by the pipeline
layout (constant_id = 0) const uint BUF_SIZE = 32;

layout(binding = 0) buffer Pos {
   uint values[ ];
};

layout (local_size_x = 4, local_size_y = 1, local_size_z = 1) in;

shared uint sharedTotal[1];

uint mod(uint x, uint N) {
    return (x % N + N) % N;
}

void main() 
{
	uint index = gl_GlobalInvocationID.x;
	if (index >= BUF_SIZE) 
		return;	

    sharedTotal[0] = 0;

    barrier();
    memoryBarrierShared();

    atomicAdd(sharedTotal[0], values[index]);

    barrier();
    memoryBarrierShared();

    uint adjacentSum = values[mod(index+1, BUF_SIZE)] + values[mod(index-1, BUF_SIZE)];

    values[index] = sharedTotal[0] + adjacentSum;
}