#include <cassert>#include <cstddef>#include <iomanip>#include <iostream>#include <numeric>#include <valarray> int main(){std::valarray<int> data(32);std::iota(std::begin(data),std::end(data),0); conststd::size_t offset=1, z=2, y=3, x=4;conststd::valarray<std::size_t> sizes{z, y, x};conststd::valarray<std::size_t> strides{15,5,1};conststd::gslice gslice=std::gslice(offset, sizes, strides);// Indices are generated according to the formula:// index[k] = offset + [0,1,2)*15 + [0,1,2,3)*5 + [0,1,2,3,4)*1// = offset + inner_product(sizes[k], strides);// where sizes[k] = {[0,z), [0,y), [0,x)}, while the rightmost index (x)// runs fastest. As a result we have following set of indices:// index[0] = 1 + 0*15 + 0*5 + 0*1 = 1// index[1] = 1 + 0*15 + 0*5 + 1*1 = 2// index[2] = 1 + 0*15 + 0*5 + 2*1 = 3// index[3] = 1 + 0*15 + 0*5 + 3*1 = 4// index[4] = 1 + 0*15 + 1*5 + 0*1 = 6// index[5] = 1 + 0*15 + 1*5 + 1*1 = 7// index[6] = 1 + 0*15 + 1*5 + 2*1 = 8// index[7] = 1 + 0*15 + 1*5 + 3*1 = 9// ...// index[22] = 1 + 1*15 + 2*5 + 2*1 = 28// index[23] = 1 + 1*15 + 2*5 + 3*1 = 29 conststd::valarray<int> indices= data[gslice];for(unsigned i=0; i!= indices.size();++i)std::cout<<std::setfill('0')<<std::setw(2)<< indices[i]<<' ';std::cout<<"\nTotal indices: "<< indices.size()<<'\n';assert(indices.size()== x* y* z); data=0; std::gslice_array<int> gslice_array= data[gslice]; gslice_array=1;// Cells that correspond to generated indices = '1', skipped cells = '0'.for(auto i: data)std::cout<< i<<' ';std::cout<<"\nSum of ones = "<< data.sum()<<'\n';}
