bench_6bit_codec.cpp

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#include <omp.h>
#include <cstdio>

#include <faiss/impl/ScalarQuantizer.h>
#include <faiss/utils/distances.h>
#include <faiss/utils/random.h>
#include <faiss/utils/utils.h>

using namespace faiss;

int main() {
    int d = 128;
    int n = 2000;

    std::vector<float> x(d * n);

    float_rand(x.data(), d * n, 12345);

    // make sure it's idempotent
    ScalarQuantizer sq(d, ScalarQuantizer::QT_6bit);

    omp_set_num_threads(1);

    sq.train(n, x.data());

    size_t code_size = sq.code_size;
    printf("code size: %ld\n", sq.code_size);

    // encode
    std::vector<uint8_t> codes(code_size * n);
    sq.compute_codes(x.data(), codes.data(), n);

    // decode
    std::vector<float> x2(d * n);
    sq.decode(codes.data(), x2.data(), n);

    printf("sqL2 recons error: %g\n",
           fvec_L2sqr(x.data(), x2.data(), n * d) / n);

    // encode again
    std::vector<uint8_t> codes2(code_size * n);
    sq.compute_codes(x2.data(), codes2.data(), n);

    size_t ndiff = 0;
    for (size_t i = 0; i < codes.size(); i++) {
        if (codes[i] != codes2[i])
            ndiff++;
    }

    printf("ndiff for idempotence: %ld / %ld\n", ndiff, codes.size());

    std::unique_ptr<ScalarQuantizer::SQDistanceComputer> dc(
            sq.get_distance_computer());
    dc->codes = codes.data();
    dc->code_size = sq.code_size;
    printf("code size: %ld\n", dc->code_size);

    double sum_dis = 0;
    double t0 = getmillisecs();
    for (int i = 0; i < n; i++) {
        dc->set_query(&x[i * d]);
        for (int j = 0; j < n; j++) {
            sum_dis += (*dc)(j);
        }
    }
    printf("distances computed in %.3f ms, checksum=%g\n",
           getmillisecs() - t0,
           sum_dis);

    return 0;
}