vs_faiss.cpp

#include <cstdio>
#include <random>

#include <faiss/IndexHNSW.h>

using idx_t = faiss::idx_t;

// https://github.com/facebookresearch/faiss/blob/main/tutorial/cpp/6-HNSW.cpp
void run_faiss() {
    int d = 64;      // dimension
    int nb = 100000; // database size
    int nq = 10000;  // nb of queries
    std::mt19937 rng;
    std::uniform_real_distribution<> distrib;
    float* xb = new float[d * nb];
    float* xq = new float[d * nq];
    for (int i = 0; i < nb; i++) {
        for (int j = 0; j < d; j++)
            xb[d * i + j] = distrib(rng);
        xb[d * i] += i / 1000.;
    }
    for (int i = 0; i < nq; i++) {
        for (int j = 0; j < d; j++)
            xq[d * i + j] = distrib(rng);
        xq[d * i] += i / 1000.;
    }
    int k = 4;
    faiss::IndexHNSWFlat index(d, 32);
    index.add(nb, xb);

    { // search xq
        idx_t* I = new idx_t[k * nq];
        float* D = new float[k * nq];
        index.search(nq, xq, k, D, I);
        printf("I=\n");
        for (int i = nq - 5; i < nq; i++) {
            for (int j = 0; j < k; j++)
                printf("%5lld ", I[i * k + j]);
            printf("\n");
        }
        printf("D=\n");
        for (int i = nq - 5; i < nq; i++) {
            for (int j = 0; j < k; j++)
                printf("%5f ", D[i * k + j]);
            printf("\n");
        }
        delete[] I;
        delete[] D;
    }
    delete[] xb;
    delete[] xq;
}

int main(int argc, char **argv) {
  run_faiss();
  return 0;
}