Function lut_dists_8b_vertical

cpp/src/quantize/multi_codebook.hpp:402–430

block size, number of dimensions of each vector

template<int B, int NBytes, class dist_t> // block size, number of dimensions of each vector
inline void lut_dists_8b_vertical(const uint8_t* codes, const dist_t* luts,
   dist_t* dists_out, int64_t N)
{
    static constexpr int lut_sz = 256;
    static constexpr int nstripes = B; // # of rows of per block
    static_assert(B > 0, "Block size B must be > 0");
    const int64_t nblocks = N / B;
    assert(N % B == 0);

    dist_t accumulators[nstripes];

    for (int64_t b = 0; b < nblocks; b++) { // for each block
        for (int i = 0; i < nstripes; i++) {
            accumulators[i] = 0; // zero dists
        }
        for (int j = 0; j < NBytes; j++) { // for each pair of dimensions
            auto lut_ptr = luts + lut_sz * j;
            for (int i = 0; i < nstripes; i++) { // for each stripe
                auto idx = *codes;
                codes++;
                accumulators[i] += lut_ptr[idx];
            }
        }
        for (int i = 0; i < nstripes; i++) { // for each stripe
            dists_out[i] = accumulators[i];
        }
        dists_out += nstripes;
    }
}

template<int NBytes, class dist_t>
inline void lut_dists_12b(const uint8_t* codes, const dist_t* luts,