xtensor-bug.cpp

#include <iostream>
#include <xtensor/xfixed.hpp>
#include <xtensor/xview.hpp>

static struct UnpackBitsLookupTable {
    xt::xtensor_fixed<uint8_t, xt::xshape<256, 8>> table;
    UnpackBitsLookupTable() {
        for (uint32_t i = 0; i < 256; i++) {
            for (uint32_t j = 0; j < 8; j++) {
                if (i & (1U << (7 - j))) {
                    table(i, j) = 1;
                    std::cout << i << "," << j << "=1\n";
                } else {
                    table(i, j) = 0;
                    std::cout << i << "," << j << "=0\n";
                }
            }
        }
    }
} BitsLookup;

int main(void) {
    xt::xarray<uint8_t> voxels = {20, 15, 33, 218, 5, 9};
    size_t num_bits = voxels.size() * 8 - 1;

    auto iv = xt::view(BitsLookup.table, xt::keep(voxels), xt::all());
    for (int i = 0; i < iv.shape(0); i++) {
        for (int j = 0; j < iv.shape(1); j++) {
            std::cout << "iv (" << i << "," << j << ") = " << (int)iv(i, j)
                      << "\n" << std::flush;
        }
    }

    auto rv = xt::reshape_view(iv, {iv.size()});
    auto fv = xt::view(rv, xt::range(0, num_bits));
    xt::xarray<uint8_t> unpacked = xt::xarray<uint8_t>::from_shape({num_bits});
    unpacked = fv;
    for (int i = 0; i < unpacked.size(); i++) {
        std::cout << "up (" << i << ") = " << (int)unpacked(i) << "\n" << std::flush;
        if (unpacked(i) != fv(i)) {
            std::cout << "mismatch at " << i << ": " << (int)unpacked(i)
                      << " != " << (int)fv(i) << "\n";
        }
    }
}