C++17 function to extract v2 from v1. Sizes of v1 is always 256. Output function is std::vector<std::vector<int>> v(16, std::vector<int>(16)). Assert output of v1 is v2.
std::vector<int>v1{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255};stdstd::vector<std::vector<int>>v2{{1,2,3,4,5,6,7},{8,9,10,11,12,13,14},{17,18,19,20,21,22,23},{24,25,26,27,28,29,30},{33,34,35,36,37,38,39},{40,41,42,43,44,45,46},{49,50,51,52,53,54,55},{56,57,58,59,60,61,62},{65,66,67,68,69,70,71},{72,73,74,75,76,77,78},{81,82,83,84,85,86,87},{88,89,90,91,92,93,94},{97,98,99,100,101,102,103},{104,105,106,107,108,109,110},{113,114,115,116,117,118,119},{120,121,122,123,124,125,126},{129,130,131,