/data/users/hoss/faiss/index_io.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.
 */

// -*- c++ -*-

#include "index_io.h"

#include <cstdio>
#include <cstdlib>

#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include "FaissAssert.h"
#include "AuxIndexStructures.h"

#include "IndexFlat.h"
#include "VectorTransform.h"
#include "IndexLSH.h"
#include "IndexPQ.h"
#include "IndexIVF.h"
#include "IndexIVFPQ.h"
#include "IndexIVFFlat.h"
#include "IndexIVFSpectralHash.h"
#include "MetaIndexes.h"
#include "IndexScalarQuantizer.h"
#include "IndexHNSW.h"
#include "OnDiskInvertedLists.h"
#include "IndexBinaryFlat.h"
#include "IndexBinaryFromFloat.h"
#include "IndexBinaryHNSW.h"
#include "IndexBinaryIVF.h"



/*************************************************************
 * The I/O format is the content of the class. For objects that are
 * inherited, like Index, a 4-character-code (fourcc) indicates which
 * child class this is an instance of.
 *
 * In this case, the fields of the parent class are written first,
 * then the ones for the child classes. Note that this requires
 * classes to be serialized to have a constructor without parameters,
 * so that the fields can be filled in later. The default constructor
 * should set reasonable defaults for all fields.
 *
 * The fourccs are assigned arbitrarily. When the class changed (added
 * or deprecated fields), the fourcc can be replaced. New code should
 * be able to read the old fourcc and fill in new classes.
 *
 * TODO: serialization to strings for use in Python pickle or Torch
 * serialization.
 *
 * TODO: in this file, the read functions that encouter errors may
 * leak memory.
 **************************************************************/



namespace faiss {

static uint32_t fourcc (const char sx[4]) {
    assert(4 == strlen(sx));
    const unsigned char *x = (unsigned char*)sx;
    return x[0] | x[1] << 8 | x[2] << 16 | x[3] << 24;
}

/*************************************************************
 * I/O macros
 *
 * we use macros so that we have a line number to report in abort
 * (). This makes debugging a lot easier. The IOReader or IOWriter is
 * always called f and thus is not passed in as a macro parameter.
 **************************************************************/


#define WRITEANDCHECK(ptr, n) {                                 \
        size_t ret = (*f)(ptr, sizeof(*(ptr)), n);              \
        FAISS_THROW_IF_NOT_FMT(ret == (n),                      \
            "write error in %s: %ld != %ld (%s)",               \
            f->name.c_str(), ret, size_t(n), strerror(errno));  \
    }

#define READANDCHECK(ptr, n) {                                  \
        size_t ret = (*f)(ptr, sizeof(*(ptr)), n);              \
        FAISS_THROW_IF_NOT_FMT(ret == (n),                      \
            "read error in %s: %ld != %ld (%s)",                \
            f->name.c_str(), ret, size_t(n), strerror(errno));  \
    }

#define WRITE1(x) WRITEANDCHECK(&(x), 1)
#define READ1(x)  READANDCHECK(&(x), 1)

#define WRITEVECTOR(vec) {                      \
        size_t size = (vec).size ();            \
        WRITEANDCHECK (&size, 1);               \
        WRITEANDCHECK ((vec).data (), size);    \
    }

// will fail if we write 256G of data at once...
#define READVECTOR(vec) {                       \
        long size;                            \
        READANDCHECK (&size, 1);                \
        FAISS_THROW_IF_NOT (size >= 0 && size < (1L << 40));  \
        (vec).resize (size);                    \
        READANDCHECK ((vec).data (), size);     \
    }

struct ScopeFileCloser {
    FILE *f;
    ScopeFileCloser (FILE *f): f (f) {}
    ~ScopeFileCloser () {fclose (f); }
};


namespace {

struct FileIOReader: IOReader {
    FILE *f = nullptr;
    bool need_close = false;

    FileIOReader(FILE *rf): f(rf) {}

    FileIOReader(const char * fname)
    {
        name = fname;
        f = fopen(fname, "rb");
        FAISS_THROW_IF_NOT_FMT (
             f, "could not open %s for reading: %s",
             fname, strerror(errno));
        need_close = true;
    }

    ~FileIOReader() override {
        if (need_close) {
            int ret = fclose(f);
            if (ret != 0) {// we cannot raise and exception in the destructor
                fprintf(stderr, "file %s close error: %s",
                        name.c_str(), strerror(errno));
            }
        }
    }

    size_t operator()(
            void *ptr, size_t size, size_t nitems) override {
        return fread(ptr, size, nitems, f);
    }

    int fileno() override {
        return ::fileno (f);
    }

};

struct FileIOWriter: IOWriter {
    FILE *f = nullptr;
    bool need_close = false;

    FileIOWriter(FILE *wf): f(wf) {}

    FileIOWriter(const char * fname)
    {
        name = fname;
        f = fopen(fname, "wb");
        FAISS_THROW_IF_NOT_FMT (
             f, "could not open %s for writing: %s",
             fname, strerror(errno));
        need_close = true;
    }

    ~FileIOWriter() override {
        if (need_close) {
            int ret = fclose(f);
            if (ret != 0) {
                // we cannot raise and exception in the destructor
                fprintf(stderr, "file %s close error: %s",
                        name.c_str(), strerror(errno));
            }
        }
    }

    size_t operator()(
            const void *ptr, size_t size, size_t nitems) override {
        return fwrite(ptr, size, nitems, f);
    }
    int fileno() override {
        return ::fileno (f);
    }

};


} // namespace


/*************************************************************
 * Write
 **************************************************************/
static void write_index_header (const Index *idx, IOWriter *f) {
    WRITE1 (idx->d);
    WRITE1 (idx->ntotal);
    Index::idx_t dummy = 1 << 20;
    WRITE1 (dummy);
    WRITE1 (dummy);
    WRITE1 (idx->is_trained);
    WRITE1 (idx->metric_type);
}

void write_VectorTransform (const VectorTransform *vt, IOWriter *f) {
    if (const LinearTransform * lt =
           dynamic_cast < const LinearTransform *> (vt)) {
        if (dynamic_cast<const RandomRotationMatrix *>(lt)) {
            uint32_t h = fourcc ("rrot");
            WRITE1 (h);
        } else if (const PCAMatrix * pca =
                   dynamic_cast<const PCAMatrix *>(lt)) {
            uint32_t h = fourcc ("PcAm");
            WRITE1 (h);
            WRITE1 (pca->eigen_power);
            WRITE1 (pca->random_rotation);
            WRITE1 (pca->balanced_bins);
            WRITEVECTOR (pca->mean);
            WRITEVECTOR (pca->eigenvalues);
            WRITEVECTOR (pca->PCAMat);
        } else {
            // generic LinearTransform (includes OPQ)
            uint32_t h = fourcc ("LTra");
            WRITE1 (h);
        }
        WRITE1 (lt->have_bias);
        WRITEVECTOR (lt->A);
        WRITEVECTOR (lt->b);
    } else if (const RemapDimensionsTransform *rdt =
               dynamic_cast<const RemapDimensionsTransform *>(vt)) {
        uint32_t h = fourcc ("RmDT");
        WRITE1 (h);
        WRITEVECTOR (rdt->map);
    } else if (const NormalizationTransform *nt =
               dynamic_cast<const NormalizationTransform *>(vt)) {
        uint32_t h = fourcc ("VNrm");
        WRITE1 (h);
        WRITE1 (nt->norm);
    } else if (const CenteringTransform *ct =
               dynamic_cast<const CenteringTransform *>(vt)) {
        uint32_t h = fourcc ("VCnt");
        WRITE1 (h);
        WRITEVECTOR (ct->mean);
    } else {
        FAISS_THROW_MSG ("cannot serialize this");
    }
    // common fields
    WRITE1 (vt->d_in);
    WRITE1 (vt->d_out);
    WRITE1 (vt->is_trained);
}

void write_ProductQuantizer (const ProductQuantizer *pq, IOWriter *f) {
    WRITE1 (pq->d);
    WRITE1 (pq->M);
    WRITE1 (pq->nbits);
    WRITEVECTOR (pq->centroids);
}

static void write_ScalarQuantizer (
        const ScalarQuantizer *ivsc, IOWriter *f) {
    WRITE1 (ivsc->qtype);
    WRITE1 (ivsc->rangestat);
    WRITE1 (ivsc->rangestat_arg);
    WRITE1 (ivsc->d);
    WRITE1 (ivsc->code_size);
    WRITEVECTOR (ivsc->trained);
}

void write_InvertedLists (const InvertedLists *ils, IOWriter *f) {
    if (ils == nullptr) {
        uint32_t h = fourcc ("il00");
        WRITE1 (h);
    } else if (const auto & ails =
               dynamic_cast<const ArrayInvertedLists *>(ils)) {
        uint32_t h = fourcc ("ilar");
        WRITE1 (h);
        WRITE1 (ails->nlist);
        WRITE1 (ails->code_size);
        // here we store either as a full or a sparse data buffer
        size_t n_non0 = 0;
        for (size_t i = 0; i < ails->nlist; i++) {
            if (ails->ids[i].size() > 0)
                n_non0++;
        }
        if (n_non0 > ails->nlist / 2) {
            uint32_t list_type = fourcc("full");
            WRITE1 (list_type);
            std::vector<size_t> sizes;
            for (size_t i = 0; i < ails->nlist; i++) {
                sizes.push_back (ails->ids[i].size());
            }
            WRITEVECTOR (sizes);
        } else {
            int list_type = fourcc("sprs"); // sparse
            WRITE1 (list_type);
            std::vector<size_t> sizes;
            for (size_t i = 0; i < ails->nlist; i++) {
                size_t n = ails->ids[i].size();
                if (n > 0) {
                    sizes.push_back (i);
                    sizes.push_back (n);
                }
            }
            WRITEVECTOR (sizes);
        }
        // make a single contiguous data buffer (useful for mmapping)
        for (size_t i = 0; i < ails->nlist; i++) {
            size_t n = ails->ids[i].size();
            if (n > 0) {
                WRITEANDCHECK (ails->codes[i].data(), n * ails->code_size);
                WRITEANDCHECK (ails->ids[i].data(), n);
            }
        }
    } else if (const auto & od =
               dynamic_cast<const OnDiskInvertedLists *>(ils)) {
        uint32_t h = fourcc ("ilod");
        WRITE1 (h);
        WRITE1 (ils->nlist);
        WRITE1 (ils->code_size);
        // this is a POD object
        WRITEVECTOR (od->lists);

        {
            std::vector<OnDiskInvertedLists::Slot> v(
                      od->slots.begin(), od->slots.end());
            WRITEVECTOR(v);
        }
        {
            std::vector<char> x(od->filename.begin(), od->filename.end());
            WRITEVECTOR(x);
        }
        WRITE1(od->totsize);

    } else {
        fprintf(stderr, "WARN! write_InvertedLists: unsupported invlist type, "
                "saving null invlist\n");
        uint32_t h = fourcc ("il00");
        WRITE1 (h);
    }
}


void write_ProductQuantizer (const ProductQuantizer*pq, const char *fname) {
    FileIOWriter writer(fname);
    write_ProductQuantizer (pq, &writer);
}

static void write_HNSW (const HNSW *hnsw, IOWriter *f) {

    WRITEVECTOR (hnsw->assign_probas);
    WRITEVECTOR (hnsw->cum_nneighbor_per_level);
    WRITEVECTOR (hnsw->levels);
    WRITEVECTOR (hnsw->offsets);
    WRITEVECTOR (hnsw->neighbors);

    WRITE1 (hnsw->entry_point);
    WRITE1 (hnsw->max_level);
    WRITE1 (hnsw->efConstruction);
    WRITE1 (hnsw->efSearch);
    WRITE1 (hnsw->upper_beam);
}

static void write_ivf_header (const IndexIVF *ivf, IOWriter *f) {
    write_index_header (ivf, f);
    WRITE1 (ivf->nlist);
    WRITE1 (ivf->nprobe);
    write_index (ivf->quantizer, f);
    WRITE1 (ivf->maintain_direct_map);
    WRITEVECTOR (ivf->direct_map);
}

void write_index (const Index *idx, IOWriter *f) {
    if (const IndexFlat * idxf = dynamic_cast<const IndexFlat *> (idx)) {
        uint32_t h = fourcc (
              idxf->metric_type == METRIC_INNER_PRODUCT ? "IxFI" :
              idxf->metric_type == METRIC_L2 ? "IxF2" : nullptr);
        WRITE1 (h);
        write_index_header (idx, f);
        WRITEVECTOR (idxf->xb);
    } else if(const IndexLSH * idxl = dynamic_cast<const IndexLSH *> (idx)) {
        uint32_t h = fourcc ("IxHe");
        WRITE1 (h);
        write_index_header (idx, f);
        WRITE1 (idxl->nbits);
        WRITE1 (idxl->rotate_data);
        WRITE1 (idxl->train_thresholds);
        WRITEVECTOR (idxl->thresholds);
        WRITE1 (idxl->bytes_per_vec);
        write_VectorTransform (&idxl->rrot, f);
        WRITEVECTOR (idxl->codes);
    } else if(const IndexPQ * idxp = dynamic_cast<const IndexPQ *> (idx)) {
        uint32_t h = fourcc ("IxPq");
        WRITE1 (h);
        write_index_header (idx, f);
        write_ProductQuantizer (&idxp->pq, f);
        WRITEVECTOR (idxp->codes);
        // search params -- maybe not useful to store?
        WRITE1 (idxp->search_type);
        WRITE1 (idxp->encode_signs);
        WRITE1 (idxp->polysemous_ht);
    } else if(const Index2Layer * idxp =
              dynamic_cast<const Index2Layer *> (idx)) {
        uint32_t h = fourcc ("Ix2L");
        WRITE1 (h);
        write_index_header (idx, f);
        write_index (idxp->q1.quantizer, f);
        WRITE1 (idxp->q1.nlist);
        WRITE1 (idxp->q1.quantizer_trains_alone);
        write_ProductQuantizer (&idxp->pq, f);
        WRITE1 (idxp->code_size_1);
        WRITE1 (idxp->code_size_2);
        WRITE1 (idxp->code_size);
        WRITEVECTOR (idxp->codes);
    } else if(const IndexScalarQuantizer * idxs =
              dynamic_cast<const IndexScalarQuantizer *> (idx)) {
        uint32_t h = fourcc ("IxSQ");
        WRITE1 (h);
        write_index_header (idx, f);
        write_ScalarQuantizer (&idxs->sq, f);
        WRITEVECTOR (idxs->codes);
    } else if(const IndexIVFFlatDedup * ivfl =
              dynamic_cast<const IndexIVFFlatDedup *> (idx)) {
        uint32_t h = fourcc ("IwFd");
        WRITE1 (h);
        write_ivf_header (ivfl, f);
        {
            std::vector<Index::idx_t> tab (2 * ivfl->instances.size());
            long i = 0;
            for (auto it = ivfl->instances.begin();
                 it != ivfl->instances.end(); ++it) {
                tab[i++] = it->first;
                tab[i++] = it->second;
            }
            WRITEVECTOR (tab);
        }
        write_InvertedLists (ivfl->invlists, f);
    } else if(const IndexIVFFlat * ivfl =
              dynamic_cast<const IndexIVFFlat *> (idx)) {
        uint32_t h = fourcc ("IwFl");
        WRITE1 (h);
        write_ivf_header (ivfl, f);
        write_InvertedLists (ivfl->invlists, f);
    } else if(const IndexIVFScalarQuantizer * ivsc =
              dynamic_cast<const IndexIVFScalarQuantizer *> (idx)) {
        uint32_t h = fourcc ("IwSq");
        WRITE1 (h);
        write_ivf_header (ivsc, f);
        write_ScalarQuantizer (&ivsc->sq, f);
        WRITE1 (ivsc->code_size);
        WRITE1 (ivsc->by_residual);
        write_InvertedLists (ivsc->invlists, f);
    } else if(const IndexIVFSpectralHash *ivsp =
              dynamic_cast<const IndexIVFSpectralHash *>(idx)) {
        uint32_t h = fourcc ("IwSh");
        WRITE1 (h);
        write_ivf_header (ivsp, f);
        write_VectorTransform (ivsp->vt, f);
        WRITE1 (ivsp->nbit);
        WRITE1 (ivsp->period);
        WRITE1 (ivsp->threshold_type);
        WRITEVECTOR (ivsp->trained);
        write_InvertedLists (ivsp->invlists, f);
    } else if(const IndexIVFPQ * ivpq =
              dynamic_cast<const IndexIVFPQ *> (idx)) {
        const IndexIVFPQR * ivfpqr = dynamic_cast<const IndexIVFPQR *> (idx);

        uint32_t h = fourcc (ivfpqr ? "IwQR" : "IwPQ");
        WRITE1 (h);
        write_ivf_header (ivpq, f);
        WRITE1 (ivpq->by_residual);
        WRITE1 (ivpq->code_size);
        write_ProductQuantizer (&ivpq->pq, f);
        write_InvertedLists (ivpq->invlists, f);
        if (ivfpqr) {
            write_ProductQuantizer (&ivfpqr->refine_pq, f);
            WRITEVECTOR (ivfpqr->refine_codes);
            WRITE1 (ivfpqr->k_factor);
        }

    } else if(const IndexPreTransform * ixpt =
              dynamic_cast<const IndexPreTransform *> (idx)) {
        uint32_t h = fourcc ("IxPT");
        WRITE1 (h);
        write_index_header (ixpt, f);
        int nt = ixpt->chain.size();
        WRITE1 (nt);
        for (int i = 0; i < nt; i++)
            write_VectorTransform (ixpt->chain[i], f);
        write_index (ixpt->index, f);
    } else if(const MultiIndexQuantizer * imiq =
              dynamic_cast<const MultiIndexQuantizer *> (idx)) {
        uint32_t h = fourcc ("Imiq");
        WRITE1 (h);
        write_index_header (imiq, f);
        write_ProductQuantizer (&imiq->pq, f);
    } else if(const IndexRefineFlat * idxrf =
              dynamic_cast<const IndexRefineFlat *> (idx)) {
        uint32_t h = fourcc ("IxRF");
        WRITE1 (h);
        write_index_header (idxrf, f);
        write_index (idxrf->base_index, f);
        write_index (&idxrf->refine_index, f);
        WRITE1 (idxrf->k_factor);
    } else if(const IndexIDMap * idxmap =
              dynamic_cast<const IndexIDMap *> (idx)) {
        uint32_t h =
            dynamic_cast<const IndexIDMap2 *> (idx) ? fourcc ("IxM2") :
            fourcc ("IxMp");
        // no need to store additional info for IndexIDMap2
        WRITE1 (h);
        write_index_header (idxmap, f);
        write_index (idxmap->index, f);
        WRITEVECTOR (idxmap->id_map);
    } else if(const IndexHNSW * idxhnsw =
              dynamic_cast<const IndexHNSW *> (idx)) {
        uint32_t h =
            dynamic_cast<const IndexHNSWFlat*>(idx)   ? fourcc("IHNf") :
            dynamic_cast<const IndexHNSWPQ*>(idx)     ? fourcc("IHNp") :
            dynamic_cast<const IndexHNSWSQ*>(idx)     ? fourcc("IHNs") :
            dynamic_cast<const IndexHNSW2Level*>(idx) ? fourcc("IHN2") :
            0;
        FAISS_THROW_IF_NOT (h != 0);
        WRITE1 (h);
        write_index_header (idxhnsw, f);
        write_HNSW (&idxhnsw->hnsw, f);
        write_index (idxhnsw->storage, f);
    } else {
      FAISS_THROW_MSG ("don't know how to serialize this type of index");
    }
}

void write_index (const Index *idx, FILE *f) {
    FileIOWriter writer(f);
    write_index (idx, &writer);
}

void write_index (const Index *idx, const char *fname) {
    FileIOWriter writer(fname);
    write_index (idx, &writer);
}

void write_VectorTransform (const VectorTransform *vt, const char *fname) {
    FileIOWriter writer(fname);
    write_VectorTransform (vt, &writer);
}

/*************************************************************
 * Read
 **************************************************************/

static void read_index_header (Index *idx, IOReader *f) {
    READ1 (idx->d);
    READ1 (idx->ntotal);
    Index::idx_t dummy;
    READ1 (dummy);
    READ1 (dummy);
    READ1 (idx->is_trained);
    READ1 (idx->metric_type);
    idx->verbose = false;
}

VectorTransform* read_VectorTransform (IOReader *f) {
    uint32_t h;
    READ1 (h);
    VectorTransform *vt = nullptr;

    if (h == fourcc ("rrot") || h == fourcc ("PCAm") ||
        h == fourcc ("LTra") || h == fourcc ("PcAm")) {
        LinearTransform *lt = nullptr;
        if (h == fourcc ("rrot")) {
            lt = new RandomRotationMatrix ();
        } else if (h == fourcc ("PCAm") ||
                   h == fourcc ("PcAm")) {
            PCAMatrix * pca = new PCAMatrix ();
            READ1 (pca->eigen_power);
            READ1 (pca->random_rotation);
            if (h == fourcc ("PcAm"))
                READ1 (pca->balanced_bins);
            READVECTOR (pca->mean);
            READVECTOR (pca->eigenvalues);
            READVECTOR (pca->PCAMat);
            lt = pca;
        } else if (h == fourcc ("LTra")) {
            lt = new LinearTransform ();
        }
        READ1 (lt->have_bias);
        READVECTOR (lt->A);
        READVECTOR (lt->b);
        FAISS_THROW_IF_NOT (lt->A.size() >= lt->d_in * lt->d_out);
        FAISS_THROW_IF_NOT (!lt->have_bias || lt->b.size() >= lt->d_out);
        lt->set_is_orthonormal();
        vt = lt;
    } else if (h == fourcc ("RmDT")) {
        RemapDimensionsTransform *rdt = new RemapDimensionsTransform ();
        READVECTOR (rdt->map);
        vt = rdt;
    } else if (h == fourcc ("VNrm")) {
        NormalizationTransform *nt = new NormalizationTransform ();
        READ1 (nt->norm);
        vt = nt;
    } else if (h == fourcc ("VCnt")) {
        CenteringTransform *ct = new CenteringTransform ();
        READVECTOR (ct->mean);
        vt = ct;
    } else {
        FAISS_THROW_MSG("fourcc not recognized");
    }
    READ1 (vt->d_in);
    READ1 (vt->d_out);
    READ1 (vt->is_trained);
    return vt;
}


static void read_ArrayInvertedLists_sizes (
         IOReader *f, std::vector<size_t> & sizes)
{
    uint32_t list_type;
    READ1(list_type);
    if (list_type == fourcc("full")) {
        size_t os = sizes.size();
        READVECTOR (sizes);
        FAISS_THROW_IF_NOT (os == sizes.size());
    } else if (list_type == fourcc("sprs")) {
        std::vector<size_t> idsizes;
        READVECTOR (idsizes);
        for (size_t j = 0; j < idsizes.size(); j += 2) {
            FAISS_THROW_IF_NOT (idsizes[j] < sizes.size());
            sizes[idsizes[j]] = idsizes[j + 1];
        }
    } else {
        FAISS_THROW_MSG ("invalid list_type");
    }
}

InvertedLists *read_InvertedLists (IOReader *f, int io_flags) {
    uint32_t h;
    READ1 (h);
    if (h == fourcc ("il00")) {
        fprintf(stderr, "read_InvertedLists:"
                " WARN! inverted lists not stored with IVF object\n");
        return nullptr;
    } else if (h == fourcc ("ilar") && !(io_flags & IO_FLAG_MMAP)) {
        auto ails = new ArrayInvertedLists (0, 0);
        READ1 (ails->nlist);
        READ1 (ails->code_size);
        ails->ids.resize (ails->nlist);
        ails->codes.resize (ails->nlist);
        std::vector<size_t> sizes (ails->nlist);
        read_ArrayInvertedLists_sizes (f, sizes);
        for (size_t i = 0; i < ails->nlist; i++) {
            ails->ids[i].resize (sizes[i]);
            ails->codes[i].resize (sizes[i] * ails->code_size);
        }
        for (size_t i = 0; i < ails->nlist; i++) {
            size_t n = ails->ids[i].size();
            if (n > 0) {
                READANDCHECK (ails->codes[i].data(), n * ails->code_size);
                READANDCHECK (ails->ids[i].data(), n);
            }
        }
        return ails;
    } else if (h == fourcc ("ilar") && (io_flags & IO_FLAG_MMAP)) {
        // then we load it as an OnDiskInvertedLists

        FileIOReader *reader = dynamic_cast<FileIOReader*>(f);
        FAISS_THROW_IF_NOT_MSG(reader, "mmap only supported for File objects");
        FILE *fdesc = reader->f;

        auto ails = new OnDiskInvertedLists ();
        READ1 (ails->nlist);
        READ1 (ails->code_size);
        ails->read_only = true;
        ails->lists.resize (ails->nlist);
        std::vector<size_t> sizes (ails->nlist);
        read_ArrayInvertedLists_sizes (f, sizes);
        size_t o0 = ftell(fdesc), o = o0;
        { // do the mmap
            struct stat buf;
            int ret = fstat (fileno(fdesc), &buf);
            FAISS_THROW_IF_NOT_FMT (ret == 0,
                                    "fstat failed: %s", strerror(errno));
            ails->totsize = buf.st_size;
            ails->ptr = (uint8_t*)mmap (nullptr, ails->totsize,
                                        PROT_READ, MAP_SHARED,
                                        fileno(fdesc), 0);
            FAISS_THROW_IF_NOT_FMT (ails->ptr != MAP_FAILED,
                            "could not mmap: %s",
                            strerror(errno));
        }

        for (size_t i = 0; i < ails->nlist; i++) {
            OnDiskInvertedLists::List & l = ails->lists[i];
            l.size = l.capacity = sizes[i];
            l.offset = o;
            o += l.size * (sizeof(OnDiskInvertedLists::idx_t) +
                           ails->code_size);
        }
        FAISS_THROW_IF_NOT(o <= ails->totsize);
        // resume normal reading of file
        fseek (fdesc, o, SEEK_SET);
        return ails;
    } else if (h == fourcc ("ilod")) {
        OnDiskInvertedLists *od = new OnDiskInvertedLists();
        od->read_only = io_flags & IO_FLAG_READ_ONLY;
        READ1 (od->nlist);
        READ1 (od->code_size);
        // this is a POD object
        READVECTOR (od->lists);
        {
            std::vector<OnDiskInvertedLists::Slot> v;
            READVECTOR(v);
            od->slots.assign(v.begin(), v.end());
        }
        {
            std::vector<char> x;
            READVECTOR(x);
            od->filename.assign(x.begin(), x.end());

            if (io_flags & IO_FLAG_ONDISK_SAME_DIR) {
                FileIOReader *reader = dynamic_cast<FileIOReader*>(f);
                FAISS_THROW_IF_NOT_MSG (
                    reader, "IO_FLAG_ONDISK_SAME_DIR only supported "
                    "when reading from file");
                std::string indexname = reader->name;
                std::string dirname = "./";
                size_t slash = indexname.find_last_of('/');
                if (slash != std::string::npos) {
                    dirname = indexname.substr(0, slash + 1);
                }
                std::string filename = od->filename;
                slash = filename.find_last_of('/');
                if (slash != std::string::npos) {
                    filename = filename.substr(slash + 1);
                }
                filename = dirname + filename;
                printf("IO_FLAG_ONDISK_SAME_DIR: "
                       "updating ondisk filename from %s to %s\n",
                       od->filename.c_str(), filename.c_str());
                od->filename = filename;
            }

        }
        READ1(od->totsize);
        od->do_mmap();
        return od;
    } else {
        FAISS_THROW_MSG ("read_InvertedLists: unsupported invlist type");
    }
}

static void read_InvertedLists (
        IndexIVF *ivf, IOReader *f, int io_flags) {
    InvertedLists *ils = read_InvertedLists (f, io_flags);
    FAISS_THROW_IF_NOT (!ils || (ils->nlist == ivf->nlist &&
                                 ils->code_size == ivf->code_size));
    ivf->invlists = ils;
    ivf->own_invlists = true;
}

static void read_InvertedLists (
    IndexBinaryIVF *ivf, IOReader *f, int io_flags) {
    InvertedLists *ils = read_InvertedLists (f, io_flags);
    FAISS_THROW_IF_NOT (!ils || (ils->nlist == ivf->nlist &&
                                 ils->code_size == ivf->code_size));
    ivf->invlists = ils;
    ivf->own_invlists = true;
}

static void read_ProductQuantizer (ProductQuantizer *pq, IOReader *f) {
    READ1 (pq->d);
    READ1 (pq->M);
    READ1 (pq->nbits);
    pq->set_derived_values ();
    READVECTOR (pq->centroids);
}

static void read_ScalarQuantizer (ScalarQuantizer *ivsc, IOReader *f) {
    READ1 (ivsc->qtype);
    READ1 (ivsc->rangestat);
    READ1 (ivsc->rangestat_arg);
    READ1 (ivsc->d);
    READ1 (ivsc->code_size);
    READVECTOR (ivsc->trained);
}


static void read_HNSW (HNSW *hnsw, IOReader *f) {
    READVECTOR (hnsw->assign_probas);
    READVECTOR (hnsw->cum_nneighbor_per_level);
    READVECTOR (hnsw->levels);
    READVECTOR (hnsw->offsets);
    READVECTOR (hnsw->neighbors);

    READ1 (hnsw->entry_point);
    READ1 (hnsw->max_level);
    READ1 (hnsw->efConstruction);
    READ1 (hnsw->efSearch);
    READ1 (hnsw->upper_beam);
}

ProductQuantizer * read_ProductQuantizer (const char*fname) {
    FileIOReader reader(fname);
    return read_ProductQuantizer(&reader);
}

ProductQuantizer * read_ProductQuantizer (IOReader *reader) {
  ProductQuantizer *pq = new ProductQuantizer();
  ScopeDeleter1<ProductQuantizer> del (pq);

  read_ProductQuantizer(pq, reader);
  del.release ();
  return pq;
}

static void read_ivf_header (
    IndexIVF *ivf, IOReader *f,
    std::vector<std::vector<Index::idx_t> > *ids = nullptr)
{
    read_index_header (ivf, f);
    READ1 (ivf->nlist);
    READ1 (ivf->nprobe);
    ivf->quantizer = read_index (f);
    ivf->own_fields = true;
    if (ids) { // used in legacy "Iv" formats
        ids->resize (ivf->nlist);
        for (size_t i = 0; i < ivf->nlist; i++)
            READVECTOR ((*ids)[i]);
    }
    READ1 (ivf->maintain_direct_map);
    READVECTOR (ivf->direct_map);
}

// used for legacy formats
static ArrayInvertedLists *set_array_invlist(
    IndexIVF *ivf, std::vector<std::vector<Index::idx_t> > &ids)
{
    ArrayInvertedLists *ail = new ArrayInvertedLists (
             ivf->nlist, ivf->code_size);
    std::swap (ail->ids, ids);
    ivf->invlists = ail;
    ivf->own_invlists = true;
    return ail;
}

static IndexIVFPQ *read_ivfpq (IOReader *f, uint32_t h, int io_flags)
{
    bool legacy = h == fourcc ("IvQR") || h == fourcc ("IvPQ");

    IndexIVFPQR *ivfpqr =
        h == fourcc ("IvQR") || h == fourcc ("IwQR") ?
        new IndexIVFPQR () : nullptr;
    IndexIVFPQ * ivpq = ivfpqr ? ivfpqr : new IndexIVFPQ ();

    std::vector<std::vector<Index::idx_t> > ids;
    read_ivf_header (ivpq, f, legacy ? &ids : nullptr);
    READ1 (ivpq->by_residual);
    READ1 (ivpq->code_size);
    read_ProductQuantizer (&ivpq->pq, f);

    if (legacy) {
        ArrayInvertedLists *ail = set_array_invlist (ivpq, ids);
        for (size_t i = 0; i < ail->nlist; i++)
            READVECTOR (ail->codes[i]);
    } else {
        read_InvertedLists (ivpq, f, io_flags);
    }

    if (ivpq->is_trained) {
        // precomputed table not stored. It is cheaper to recompute it
        ivpq->use_precomputed_table = 0;
        if (ivpq->by_residual)
            ivpq->precompute_table ();
        if (ivfpqr) {
            read_ProductQuantizer (&ivfpqr->refine_pq, f);
            READVECTOR (ivfpqr->refine_codes);
            READ1 (ivfpqr->k_factor);
        }
    }
    return ivpq;
}

int read_old_fmt_hack = 0;

Index *read_index (IOReader *f, int io_flags) {
    Index * idx = nullptr;
    uint32_t h;
    READ1 (h);
    if (h == fourcc ("IxFI") || h == fourcc ("IxF2")) {
        IndexFlat *idxf;
        if (h == fourcc ("IxFI")) idxf = new IndexFlatIP ();
        else                      idxf = new IndexFlatL2 ();
        read_index_header (idxf, f);
        READVECTOR (idxf->xb);
        FAISS_THROW_IF_NOT (idxf->xb.size() == idxf->ntotal * idxf->d);
        // leak!
        idx = idxf;
    } else if (h == fourcc("IxHE") || h == fourcc("IxHe")) {
        IndexLSH * idxl = new IndexLSH ();
        read_index_header (idxl, f);
        READ1 (idxl->nbits);
        READ1 (idxl->rotate_data);
        READ1 (idxl->train_thresholds);
        READVECTOR (idxl->thresholds);
        READ1 (idxl->bytes_per_vec);
        if (h == fourcc("IxHE")) {
            FAISS_THROW_IF_NOT_FMT (idxl->nbits % 64 == 0,
                            "can only read old format IndexLSH with "
                            "nbits multiple of 64 (got %d)",
                            (int) idxl->nbits);
            // leak
            idxl->bytes_per_vec *= 8;
        }
        {
            RandomRotationMatrix *rrot = dynamic_cast<RandomRotationMatrix *>
                (read_VectorTransform (f));
            FAISS_THROW_IF_NOT_MSG(rrot, "expected a random rotation");
            idxl->rrot = *rrot;
            delete rrot;
        }
        READVECTOR (idxl->codes);
        FAISS_THROW_IF_NOT (idxl->rrot.d_in == idxl->d &&
                      idxl->rrot.d_out == idxl->nbits);
        FAISS_THROW_IF_NOT (
               idxl->codes.size() == idxl->ntotal * idxl->bytes_per_vec);
        idx = idxl;
    } else if (h == fourcc ("IxPQ") || h == fourcc ("IxPo") ||
               h == fourcc ("IxPq")) {
        // IxPQ and IxPo were merged into the same IndexPQ object
        IndexPQ * idxp =new IndexPQ ();
        read_index_header (idxp, f);
        read_ProductQuantizer (&idxp->pq, f);
        READVECTOR (idxp->codes);
        if (h == fourcc ("IxPo") || h == fourcc ("IxPq")) {
            READ1 (idxp->search_type);
            READ1 (idxp->encode_signs);
            READ1 (idxp->polysemous_ht);
        }
        // Old versoins of PQ all had metric_type set to INNER_PRODUCT
        // when they were in fact using L2. Therefore, we force metric type
        // to L2 when the old format is detected
        if (h == fourcc ("IxPQ") || h == fourcc ("IxPo")) {
            idxp->metric_type = METRIC_L2;
        }
        idx = idxp;
    } else if (h == fourcc ("IvFl") || h == fourcc("IvFL")) { // legacy
        IndexIVFFlat * ivfl = new IndexIVFFlat ();
        std::vector<std::vector<Index::idx_t> > ids;
        read_ivf_header (ivfl, f, &ids);
        ivfl->code_size = ivfl->d * sizeof(float);
        ArrayInvertedLists *ail = set_array_invlist (ivfl, ids);

        if (h == fourcc ("IvFL")) {
            for (size_t i = 0; i < ivfl->nlist; i++) {
                READVECTOR (ail->codes[i]);
            }
        } else { // old format
            for (size_t i = 0; i < ivfl->nlist; i++) {
                std::vector<float> vec;
                READVECTOR (vec);
                ail->codes[i].resize(vec.size() * sizeof(float));
                memcpy(ail->codes[i].data(), vec.data(),
                       ail->codes[i].size());
            }
        }
        idx = ivfl;
    } else if (h == fourcc ("IwFd")) {
        IndexIVFFlatDedup * ivfl = new IndexIVFFlatDedup ();
        read_ivf_header (ivfl, f);
        ivfl->code_size = ivfl->d * sizeof(float);
        {
            std::vector<Index::idx_t> tab;
            READVECTOR (tab);
            for (long i = 0; i < tab.size(); i += 2) {
                std::pair<Index::idx_t, Index::idx_t>
                    pair (tab[i], tab[i + 1]);
                ivfl->instances.insert (pair);
            }
        }
        read_InvertedLists (ivfl, f, io_flags);
        idx = ivfl;
    } else if (h == fourcc ("IwFl")) {
        IndexIVFFlat * ivfl = new IndexIVFFlat ();
        read_ivf_header (ivfl, f);
        ivfl->code_size = ivfl->d * sizeof(float);
        read_InvertedLists (ivfl, f, io_flags);
        idx = ivfl;
    } else if (h == fourcc ("IxSQ")) {
        IndexScalarQuantizer * idxs = new IndexScalarQuantizer ();
        read_index_header (idxs, f);
        read_ScalarQuantizer (&idxs->sq, f);
        READVECTOR (idxs->codes);
        idxs->code_size = idxs->sq.code_size;
        idx = idxs;
    } else if(h == fourcc ("IvSQ")) { // legacy
        IndexIVFScalarQuantizer * ivsc = new IndexIVFScalarQuantizer();
        std::vector<std::vector<Index::idx_t> > ids;
        read_ivf_header (ivsc, f, &ids);
        read_ScalarQuantizer (&ivsc->sq, f);
        READ1 (ivsc->code_size);
        ArrayInvertedLists *ail = set_array_invlist (ivsc, ids);
        for(int i = 0; i < ivsc->nlist; i++)
            READVECTOR (ail->codes[i]);
        idx = ivsc;
    } else if(h == fourcc ("IwSQ") || h == fourcc ("IwSq")) {
        IndexIVFScalarQuantizer * ivsc = new IndexIVFScalarQuantizer();
        read_ivf_header (ivsc, f);
        read_ScalarQuantizer (&ivsc->sq, f);
        READ1 (ivsc->code_size);
        if (h == fourcc ("IwSQ")) {
            ivsc->by_residual = true;
        } else {
            READ1 (ivsc->by_residual);
        }
        read_InvertedLists (ivsc, f, io_flags);
        idx = ivsc;
    } else if(h == fourcc ("IwSh")) {
        IndexIVFSpectralHash *ivsp = new IndexIVFSpectralHash ();
        read_ivf_header (ivsp, f);
        ivsp->vt = read_VectorTransform (f);
        ivsp->own_fields = true;
        READ1 (ivsp->nbit);
        // not stored by write_ivf_header
        ivsp->code_size = (ivsp->nbit + 7) / 8;
        READ1 (ivsp->period);
        READ1 (ivsp->threshold_type);
        READVECTOR (ivsp->trained);
        read_InvertedLists (ivsp, f, io_flags);
        idx = ivsp;
    } else if(h == fourcc ("IvPQ") || h == fourcc ("IvQR") ||
              h == fourcc ("IwPQ") || h == fourcc ("IwQR")) {

        idx = read_ivfpq (f, h, io_flags);

    } else if(h == fourcc ("IxPT")) {
        IndexPreTransform * ixpt = new IndexPreTransform();
        ixpt->own_fields = true;
        read_index_header (ixpt, f);
        int nt;
        if (read_old_fmt_hack == 2) {
            nt = 1;
        } else {
            READ1 (nt);
        }
        for (int i = 0; i < nt; i++) {
            ixpt->chain.push_back (read_VectorTransform (f));
        }
        ixpt->index = read_index (f, io_flags);
        idx = ixpt;
    } else if(h == fourcc ("Imiq")) {
        MultiIndexQuantizer * imiq = new MultiIndexQuantizer ();
        read_index_header (imiq, f);
        read_ProductQuantizer (&imiq->pq, f);
        idx = imiq;
    } else if(h == fourcc ("IxRF")) {
        IndexRefineFlat *idxrf = new IndexRefineFlat ();
        read_index_header (idxrf, f);
        idxrf->base_index = read_index(f, io_flags);
        idxrf->own_fields = true;
        IndexFlat *rf = dynamic_cast<IndexFlat*> (read_index (f, io_flags));
        std::swap (*rf, idxrf->refine_index);
        delete rf;
        READ1 (idxrf->k_factor);
        idx = idxrf;
    } else if(h == fourcc ("IxMp") || h == fourcc ("IxM2")) {
        bool is_map2 = h == fourcc ("IxM2");
        IndexIDMap * idxmap = is_map2 ? new IndexIDMap2 () : new IndexIDMap ();
        read_index_header (idxmap, f);
        idxmap->index = read_index (f, io_flags);
        idxmap->own_fields = true;
        READVECTOR (idxmap->id_map);
        if (is_map2) {
            static_cast<IndexIDMap2*>(idxmap)->construct_rev_map ();
        }
        idx = idxmap;
    } else if (h == fourcc ("Ix2L")) {
        Index2Layer * idxp = new Index2Layer ();
        read_index_header (idxp, f);
        idxp->q1.quantizer = read_index (f, io_flags);
        READ1 (idxp->q1.nlist);
        READ1 (idxp->q1.quantizer_trains_alone);
        read_ProductQuantizer (&idxp->pq, f);
        READ1 (idxp->code_size_1);
        READ1 (idxp->code_size_2);
        READ1 (idxp->code_size);
        READVECTOR (idxp->codes);
        idx = idxp;
    } else if(h == fourcc("IHNf") || h == fourcc("IHNp") ||
              h == fourcc("IHNs") || h == fourcc("IHN2")) {
        IndexHNSW *idxhnsw = nullptr;
        if (h == fourcc("IHNf")) idxhnsw = new IndexHNSWFlat ();
        if (h == fourcc("IHNp")) idxhnsw = new IndexHNSWPQ ();
        if (h == fourcc("IHNs")) idxhnsw = new IndexHNSWSQ ();
        if (h == fourcc("IHN2")) idxhnsw = new IndexHNSW2Level ();
        read_index_header (idxhnsw, f);
        read_HNSW (&idxhnsw->hnsw, f);
        idxhnsw->storage = read_index (f, io_flags);
        idxhnsw->own_fields = true;
        if (h == fourcc("IHNp")) {
            dynamic_cast<IndexPQ*>(idxhnsw->storage)->pq.compute_sdc_table ();
        }
        idx = idxhnsw;
    } else {
        FAISS_THROW_FMT("Index type 0x%08x not supported\n", h);
        idx = nullptr;
    }
    return idx;
}


Index *read_index (FILE * f, int io_flags) {
    FileIOReader reader(f);
    return read_index(&reader, io_flags);
}

Index *read_index (const char *fname, int io_flags) {
    FileIOReader reader(fname);
    Index *idx = read_index (&reader, io_flags);
    return idx;
}

VectorTransform *read_VectorTransform (const char *fname) {
    FileIOReader reader(fname);
    VectorTransform *vt = read_VectorTransform (&reader);
    return vt;
}

/*************************************************************
 * cloning functions
 **************************************************************/



Index * clone_index (const Index *index)
{
    Cloner cl;
    return cl.clone_Index (index);
}

// assumes there is a copy constructor ready. Always try from most
// specific to most general
#define TRYCLONE(classname, obj) \
    if (const classname *clo = dynamic_cast<const classname *>(obj)) { \
        return new classname(*clo); \
    } else

VectorTransform *Cloner::clone_VectorTransform (const VectorTransform *vt)
{
    TRYCLONE (RemapDimensionsTransform, vt)
    TRYCLONE (OPQMatrix, vt)
    TRYCLONE (PCAMatrix, vt)
    TRYCLONE (RandomRotationMatrix, vt)
    TRYCLONE (LinearTransform, vt)
    {
      FAISS_THROW_MSG("clone not supported for this type of VectorTransform");
    }
    return nullptr;
}

IndexIVF * Cloner::clone_IndexIVF (const IndexIVF *ivf)
{
    TRYCLONE (IndexIVFPQR, ivf)
    TRYCLONE (IndexIVFPQ, ivf)
    TRYCLONE (IndexIVFFlat, ivf)
    TRYCLONE (IndexIVFScalarQuantizer, ivf)
    {
      FAISS_THROW_MSG("clone not supported for this type of IndexIVF");
    }
    return nullptr;
}

Index *Cloner::clone_Index (const Index *index)
{
    TRYCLONE (IndexPQ, index)
    TRYCLONE (IndexLSH, index)
    TRYCLONE (IndexFlatL2, index)
    TRYCLONE (IndexFlatIP, index)
    TRYCLONE (IndexFlat, index)
    TRYCLONE (IndexScalarQuantizer, index)
    TRYCLONE (MultiIndexQuantizer, index)
    if (const IndexIVF * ivf = dynamic_cast<const IndexIVF*>(index)) {
        IndexIVF *res = clone_IndexIVF (ivf);
        if (ivf->invlists == nullptr) {
            res->invlists = nullptr;
        } else if (auto *ails = dynamic_cast<const ArrayInvertedLists*>
                   (ivf->invlists)) {
            res->invlists = new ArrayInvertedLists(*ails);
            res->own_invlists = true;
        } else {
            FAISS_THROW_MSG( "clone not supported for this type of inverted lists");
        }
        res->own_fields = true;
        res->quantizer = clone_Index (ivf->quantizer);
        return res;
    } else if (const IndexPreTransform * ipt =
               dynamic_cast<const IndexPreTransform*> (index)) {
        IndexPreTransform *res = new IndexPreTransform ();
        res->d = ipt->d;
        res->index = clone_Index (ipt->index);
        for (int i = 0; i < ipt->chain.size(); i++)
            res->chain.push_back (clone_VectorTransform (ipt->chain[i]));
        res->own_fields = true;
        return res;
    } else if (const IndexIDMap *idmap =
               dynamic_cast<const IndexIDMap*> (index)) {
        IndexIDMap *res = new IndexIDMap (*idmap);
        res->own_fields = true;
        res->index = clone_Index (idmap->index);
        return res;
    } else {
        FAISS_THROW_MSG( "clone not supported for this type of Index");
    }
    return nullptr;
}


static void write_index_binary_header (const IndexBinary *idx, IOWriter *f) {
    WRITE1 (idx->d);
    WRITE1 (idx->code_size);
    WRITE1 (idx->ntotal);
    WRITE1 (idx->is_trained);
    WRITE1 (idx->metric_type);
}

static void write_binary_ivf_header (const IndexBinaryIVF *ivf, IOWriter *f) {
    write_index_binary_header (ivf, f);
    WRITE1 (ivf->nlist);
    WRITE1 (ivf->nprobe);
    write_index_binary (ivf->quantizer, f);
    WRITE1 (ivf->maintain_direct_map);
    WRITEVECTOR (ivf->direct_map);
}

void write_index_binary (const IndexBinary *idx, IOWriter *f) {
    if (const IndexBinaryFlat *idxf =
        dynamic_cast<const IndexBinaryFlat *> (idx)) {
        uint32_t h = fourcc ("IBxF");
        WRITE1 (h);
        write_index_binary_header (idx, f);
        WRITEVECTOR (idxf->xb);
    } else if (const IndexBinaryIVF *ivf =
               dynamic_cast<const IndexBinaryIVF *> (idx)) {
        uint32_t h = fourcc ("IBwF");
        WRITE1 (h);
        write_binary_ivf_header (ivf, f);
        write_InvertedLists (ivf->invlists, f);
    } else if(const IndexBinaryFromFloat * idxff =
              dynamic_cast<const IndexBinaryFromFloat *> (idx)) {
        uint32_t h = fourcc ("IBFf");
        WRITE1 (h);
        write_index_binary_header (idxff, f);
        write_index (idxff->index, f);
    } else if (const IndexBinaryHNSW *idxhnsw =
               dynamic_cast<const IndexBinaryHNSW *> (idx)) {
        uint32_t h = fourcc ("IBHf");
        WRITE1 (h);
        write_index_binary_header (idxhnsw, f);
        write_HNSW (&idxhnsw->hnsw, f);
        write_index_binary (idxhnsw->storage, f);
    } else {
        FAISS_THROW_MSG ("don't know how to serialize this type of index");
    }
}

void write_index_binary (const IndexBinary *idx, FILE *f) {
    FileIOWriter writer(f);
    write_index_binary(idx, &writer);
}

void write_index_binary (const IndexBinary *idx, const char *fname) {
    FileIOWriter writer(fname);
    write_index_binary (idx, &writer);
}

static void read_index_binary_header (IndexBinary *idx, IOReader *f) {
    READ1 (idx->d);
    READ1 (idx->code_size);
    READ1 (idx->ntotal);
    READ1 (idx->is_trained);
    READ1 (idx->metric_type);
    idx->verbose = false;
}

static void read_binary_ivf_header (
    IndexBinaryIVF *ivf, IOReader *f,
    std::vector<std::vector<Index::idx_t> > *ids = nullptr)
{
    read_index_binary_header (ivf, f);
    READ1 (ivf->nlist);
    READ1 (ivf->nprobe);
    ivf->quantizer = read_index_binary (f);
    ivf->own_fields = true;
    if (ids) { // used in legacy "Iv" formats
        ids->resize (ivf->nlist);
        for (size_t i = 0; i < ivf->nlist; i++)
            READVECTOR ((*ids)[i]);
    }
    READ1 (ivf->maintain_direct_map);
    READVECTOR (ivf->direct_map);
}

IndexBinary *read_index_binary (IOReader *f, int io_flags) {
    IndexBinary * idx = nullptr;
    uint32_t h;
    READ1 (h);
    if (h == fourcc ("IBxF")) {
        IndexBinaryFlat *idxf = new IndexBinaryFlat ();
        read_index_binary_header (idxf, f);
        READVECTOR (idxf->xb);
        FAISS_THROW_IF_NOT (idxf->xb.size() == idxf->ntotal * idxf->code_size);
        // leak!
        idx = idxf;
    } else if (h == fourcc ("IBwF")) {
        IndexBinaryIVF *ivf = new IndexBinaryIVF ();
        read_binary_ivf_header (ivf, f);
        read_InvertedLists (ivf, f, io_flags);
        idx = ivf;
    } else if (h == fourcc ("IBFf")) {
        IndexBinaryFromFloat *idxff = new IndexBinaryFromFloat ();
        read_index_binary_header (idxff, f);
        idxff->own_fields = true;
        idxff->index = read_index (f, io_flags);
        idx = idxff;
    } else if (h == fourcc ("IBHf")) {
        IndexBinaryHNSW *idxhnsw = new IndexBinaryHNSW ();
        read_index_binary_header (idxhnsw, f);
        read_HNSW (&idxhnsw->hnsw, f);
        idxhnsw->storage = read_index_binary (f, io_flags);
        idxhnsw->own_fields = true;
        idx = idxhnsw;
    } else {
        FAISS_THROW_FMT("Index type 0x%08x not supported\n", h);
        idx = nullptr;
    }
    return idx;
}

IndexBinary *read_index_binary (FILE * f, int io_flags) {
    FileIOReader reader(f);
    return read_index_binary(&reader, io_flags);
}

IndexBinary *read_index_binary (const char *fname, int io_flags) {
    FileIOReader reader(fname);
    IndexBinary *idx = read_index_binary (&reader, io_flags);
    return idx;
}


} // namespace faiss