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

#include <faiss/invlists/InvertedLists.h>

#include <cstdio>
#include <memory>

#include <faiss/impl/FaissAssert.h>
#include <faiss/utils/utils.h>

namespace faiss {

InvertedListsIterator::~InvertedListsIterator() {}

/*****************************************
 * InvertedLists implementation
 ******************************************/

InvertedLists::InvertedLists(size_t nlist, size_t code_size)
        : nlist(nlist), code_size(code_size) {}

InvertedLists::~InvertedLists() {}

idx_t InvertedLists::get_single_id(size_t list_no, size_t offset) const {
    assert(offset < list_size(list_no));
    const idx_t* ids = get_ids(list_no);
    idx_t id = ids[offset];
    release_ids(list_no, ids);
    return id;
}

void InvertedLists::release_codes(size_t, const uint8_t*) const {}

void InvertedLists::release_ids(size_t, const idx_t*) const {}

void InvertedLists::prefetch_lists(const idx_t*, int) const {}

const uint8_t* InvertedLists::get_single_code(size_t list_no, size_t offset)
        const {
    assert(offset < list_size(list_no));
    return get_codes(list_no) + offset * code_size;
}

size_t InvertedLists::add_entry(
        size_t list_no,
        idx_t theid,
        const uint8_t* code,
        void* /*inverted_list_context*/) {
    return add_entries(list_no, 1, &theid, code);
}

void InvertedLists::update_entry(
        size_t list_no,
        size_t offset,
        idx_t id,
        const uint8_t* code) {
    update_entries(list_no, offset, 1, &id, code);
}

void InvertedLists::reset() {
    for (size_t i = 0; i < nlist; i++) {
        resize(i, 0);
    }
}

void InvertedLists::merge_from(InvertedLists* oivf, size_t add_id) {
#pragma omp parallel for
    for (idx_t i = 0; i < nlist; i++) {
        size_t list_size = oivf->list_size(i);
        ScopedIds ids(oivf, i);
        if (add_id == 0) {
            add_entries(i, list_size, ids.get(), ScopedCodes(oivf, i).get());
        } else {
            std::vector<idx_t> new_ids(list_size);

            for (size_t j = 0; j < list_size; j++) {
                new_ids[j] = ids[j] + add_id;
            }
            add_entries(
                    i, list_size, new_ids.data(), ScopedCodes(oivf, i).get());
        }
        oivf->resize(i, 0);
    }
}

size_t InvertedLists::copy_subset_to(
        InvertedLists& oivf,
        subset_type_t subset_type,
        idx_t a1,
        idx_t a2) const {
    FAISS_THROW_IF_NOT(nlist == oivf.nlist);
    FAISS_THROW_IF_NOT(code_size == oivf.code_size);
    FAISS_THROW_IF_NOT_FMT(
            subset_type >= 0 && subset_type <= 4,
            "subset type %d not implemented",
            subset_type);
    size_t accu_n = 0;
    size_t accu_a1 = 0;
    size_t accu_a2 = 0;
    size_t n_added = 0;

    size_t ntotal = 0;
    if (subset_type == 2) {
        ntotal = compute_ntotal();
    }

    for (idx_t list_no = 0; list_no < nlist; list_no++) {
        size_t n = list_size(list_no);
        ScopedIds ids_in(this, list_no);

        if (subset_type == SUBSET_TYPE_ID_RANGE) {
            for (idx_t i = 0; i < n; i++) {
                idx_t id = ids_in[i];
                if (a1 <= id && id < a2) {
                    oivf.add_entry(
                            list_no,
                            get_single_id(list_no, i),
                            ScopedCodes(this, list_no, i).get());
                    n_added++;
                }
            }
        } else if (subset_type == SUBSET_TYPE_ID_MOD) {
            for (idx_t i = 0; i < n; i++) {
                idx_t id = ids_in[i];
                if (id % a1 == a2) {
                    oivf.add_entry(
                            list_no,
                            get_single_id(list_no, i),
                            ScopedCodes(this, list_no, i).get());
                    n_added++;
                }
            }
        } else if (subset_type == SUBSET_TYPE_ELEMENT_RANGE) {
            // see what is allocated to a1 and to a2
            size_t next_accu_n = accu_n + n;
            size_t next_accu_a1 = next_accu_n * a1 / ntotal;
            size_t i1 = next_accu_a1 - accu_a1;
            size_t next_accu_a2 = next_accu_n * a2 / ntotal;
            size_t i2 = next_accu_a2 - accu_a2;

            for (idx_t i = i1; i < i2; i++) {
                oivf.add_entry(
                        list_no,
                        get_single_id(list_no, i),
                        ScopedCodes(this, list_no, i).get());
            }

            n_added += i2 - i1;
            accu_a1 = next_accu_a1;
            accu_a2 = next_accu_a2;
        } else if (subset_type == SUBSET_TYPE_INVLIST_FRACTION) {
            size_t i1 = n * a2 / a1;
            size_t i2 = n * (a2 + 1) / a1;

            for (idx_t i = i1; i < i2; i++) {
                oivf.add_entry(
                        list_no,
                        get_single_id(list_no, i),
                        ScopedCodes(this, list_no, i).get());
            }

            n_added += i2 - i1;
        } else if (subset_type == SUBSET_TYPE_INVLIST) {
            if (list_no >= a1 && list_no < a2) {
                oivf.add_entries(
                        list_no,
                        n,
                        ScopedIds(this, list_no).get(),
                        ScopedCodes(this, list_no).get());
                n_added += n;
            }
        }
        accu_n += n;
    }
    return n_added;
}

double InvertedLists::imbalance_factor() const {
    std::vector<int> hist(nlist);

    for (size_t i = 0; i < nlist; i++) {
        hist[i] = list_size(i);
    }

    return faiss::imbalance_factor(nlist, hist.data());
}

void InvertedLists::print_stats() const {
    std::vector<int> sizes(40);
    for (size_t i = 0; i < nlist; i++) {
        for (size_t j = 0; j < sizes.size(); j++) {
            if ((list_size(i) >> j) == 0) {
                sizes[j]++;
                break;
            }
        }
    }
    for (size_t i = 0; i < sizes.size(); i++) {
        if (sizes[i]) {
            printf("list size in < %zu: %d instances\n",
                   static_cast<size_t>(1) << i,
                   sizes[i]);
        }
    }
}

size_t InvertedLists::compute_ntotal() const {
    size_t tot = 0;
    for (size_t i = 0; i < nlist; i++) {
        tot += list_size(i);
    }
    return tot;
}

bool InvertedLists::is_empty(size_t list_no, void* inverted_list_context)
        const {
    if (use_iterator) {
        return !std::unique_ptr<InvertedListsIterator>(
                        get_iterator(list_no, inverted_list_context))
                        ->is_available();
    } else {
        FAISS_THROW_IF_NOT(inverted_list_context == nullptr);
        return list_size(list_no) == 0;
    }
}

// implemnent iterator on top of get_codes / get_ids
namespace {

struct CodeArrayIterator : InvertedListsIterator {
    size_t list_size;
    size_t code_size;
    InvertedLists::ScopedCodes codes;
    InvertedLists::ScopedIds ids;
    size_t idx = 0;

    CodeArrayIterator(const InvertedLists* il, size_t list_no)
            : list_size(il->list_size(list_no)),
              code_size(il->code_size),
              codes(il, list_no),
              ids(il, list_no) {}

    bool is_available() const override {
        return idx < list_size;
    }
    void next() override {
        idx++;
    }
    std::pair<idx_t, const uint8_t*> get_id_and_codes() override {
        return {ids[idx], codes.get() + code_size * idx};
    }
};

} // namespace

InvertedListsIterator* InvertedLists::get_iterator(
        size_t list_no,
        void* inverted_list_context) const {
    FAISS_THROW_IF_NOT(inverted_list_context == nullptr);
    return new CodeArrayIterator(this, list_no);
}

/*****************************************
 * ArrayInvertedLists implementation
 ******************************************/

ArrayInvertedLists::ArrayInvertedLists(size_t nlist, size_t code_size)
        : InvertedLists(nlist, code_size) {
    ids.resize(nlist);
    codes.resize(nlist);
}

size_t ArrayInvertedLists::add_entries(
        size_t list_no,
        size_t n_entry,
        const idx_t* ids_in,
        const uint8_t* code) {
    if (n_entry == 0)
        return 0;
    assert(list_no < nlist);
    size_t o = ids[list_no].size();
    ids[list_no].resize(o + n_entry);
    memcpy(&ids[list_no][o], ids_in, sizeof(ids_in[0]) * n_entry);
    codes[list_no].resize((o + n_entry) * code_size);
    memcpy(&codes[list_no][o * code_size], code, code_size * n_entry);
    return o;
}

size_t ArrayInvertedLists::list_size(size_t list_no) const {
    assert(list_no < nlist);
    return ids[list_no].size();
}

bool ArrayInvertedLists::is_empty(size_t list_no, void* inverted_list_context)
        const {
    FAISS_THROW_IF_NOT(inverted_list_context == nullptr);
    return ids[list_no].size() == 0;
}

const uint8_t* ArrayInvertedLists::get_codes(size_t list_no) const {
    assert(list_no < nlist);
    return codes[list_no].data();
}

const idx_t* ArrayInvertedLists::get_ids(size_t list_no) const {
    assert(list_no < nlist);
    return ids[list_no].data();
}

void ArrayInvertedLists::resize(size_t list_no, size_t new_size) {
    ids[list_no].resize(new_size);
    codes[list_no].resize(new_size * code_size);
}

void ArrayInvertedLists::update_entries(
        size_t list_no,
        size_t offset,
        size_t n_entry,
        const idx_t* ids_in,
        const uint8_t* codes_in) {
    assert(list_no < nlist);
    assert(n_entry + offset <= ids[list_no].size());
    memcpy(&ids[list_no][offset], ids_in, sizeof(ids_in[0]) * n_entry);
    memcpy(&codes[list_no][offset * code_size], codes_in, code_size * n_entry);
}

void ArrayInvertedLists::permute_invlists(const idx_t* map) {
    std::vector<std::vector<uint8_t>> new_codes(nlist);
    std::vector<std::vector<idx_t>> new_ids(nlist);

    for (size_t i = 0; i < nlist; i++) {
        size_t o = map[i];
        FAISS_THROW_IF_NOT(o < nlist);
        std::swap(new_codes[i], codes[o]);
        std::swap(new_ids[i], ids[o]);
    }
    std::swap(codes, new_codes);
    std::swap(ids, new_ids);
}

ArrayInvertedLists::~ArrayInvertedLists() {}

/*****************************************************************
 * Meta-inverted list implementations
 *****************************************************************/

size_t ReadOnlyInvertedLists::add_entries(
        size_t,
        size_t,
        const idx_t*,
        const uint8_t*) {
    FAISS_THROW_MSG("not implemented");
}

void ReadOnlyInvertedLists::update_entries(
        size_t,
        size_t,
        size_t,
        const idx_t*,
        const uint8_t*) {
    FAISS_THROW_MSG("not implemented");
}

void ReadOnlyInvertedLists::resize(size_t, size_t) {
    FAISS_THROW_MSG("not implemented");
}

/*****************************************
 * HStackInvertedLists implementation
 ******************************************/

HStackInvertedLists::HStackInvertedLists(int nil, const InvertedLists** ils_in)
        : ReadOnlyInvertedLists(
                  nil > 0 ? ils_in[0]->nlist : 0,
                  nil > 0 ? ils_in[0]->code_size : 0) {
    FAISS_THROW_IF_NOT(nil > 0);
    for (int i = 0; i < nil; i++) {
        ils.push_back(ils_in[i]);
        FAISS_THROW_IF_NOT(
                ils_in[i]->code_size == code_size && ils_in[i]->nlist == nlist);
    }
}

size_t HStackInvertedLists::list_size(size_t list_no) const {
    size_t sz = 0;
    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        sz += il->list_size(list_no);
    }
    return sz;
}

const uint8_t* HStackInvertedLists::get_codes(size_t list_no) const {
    uint8_t *codes = new uint8_t[code_size * list_size(list_no)], *c = codes;

    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        size_t sz = il->list_size(list_no) * code_size;
        if (sz > 0) {
            memcpy(c, ScopedCodes(il, list_no).get(), sz);
            c += sz;
        }
    }
    return codes;
}

const uint8_t* HStackInvertedLists::get_single_code(
        size_t list_no,
        size_t offset) const {
    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        size_t sz = il->list_size(list_no);
        if (offset < sz) {
            // here we have to copy the code, otherwise it will crash at dealloc
            uint8_t* code = new uint8_t[code_size];
            memcpy(code, ScopedCodes(il, list_no, offset).get(), code_size);
            return code;
        }
        offset -= sz;
    }
    FAISS_THROW_FMT("offset %zd unknown", offset);
}

void HStackInvertedLists::release_codes(size_t, const uint8_t* codes) const {
    delete[] codes;
}

const idx_t* HStackInvertedLists::get_ids(size_t list_no) const {
    idx_t *ids = new idx_t[list_size(list_no)], *c = ids;

    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        size_t sz = il->list_size(list_no);
        if (sz > 0) {
            memcpy(c, ScopedIds(il, list_no).get(), sz * sizeof(idx_t));
            c += sz;
        }
    }
    return ids;
}

idx_t HStackInvertedLists::get_single_id(size_t list_no, size_t offset) const {
    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        size_t sz = il->list_size(list_no);
        if (offset < sz) {
            return il->get_single_id(list_no, offset);
        }
        offset -= sz;
    }
    FAISS_THROW_FMT("offset %zd unknown", offset);
}

void HStackInvertedLists::release_ids(size_t, const idx_t* ids) const {
    delete[] ids;
}

void HStackInvertedLists::prefetch_lists(const idx_t* list_nos, int nlist)
        const {
    for (int i = 0; i < ils.size(); i++) {
        const InvertedLists* il = ils[i];
        il->prefetch_lists(list_nos, nlist);
    }
}

/*****************************************
 * SliceInvertedLists implementation
 ******************************************/

namespace {

idx_t translate_list_no(const SliceInvertedLists* sil, idx_t list_no) {
    FAISS_THROW_IF_NOT(list_no >= 0 && list_no < sil->nlist);
    return list_no + sil->i0;
}

} // namespace

SliceInvertedLists::SliceInvertedLists(
        const InvertedLists* il,
        idx_t i0,
        idx_t i1)
        : ReadOnlyInvertedLists(i1 - i0, il->code_size),
          il(il),
          i0(i0),
          i1(i1) {}

size_t SliceInvertedLists::list_size(size_t list_no) const {
    return il->list_size(translate_list_no(this, list_no));
}

const uint8_t* SliceInvertedLists::get_codes(size_t list_no) const {
    return il->get_codes(translate_list_no(this, list_no));
}

const uint8_t* SliceInvertedLists::get_single_code(
        size_t list_no,
        size_t offset) const {
    return il->get_single_code(translate_list_no(this, list_no), offset);
}

void SliceInvertedLists::release_codes(size_t list_no, const uint8_t* codes)
        const {
    return il->release_codes(translate_list_no(this, list_no), codes);
}

const idx_t* SliceInvertedLists::get_ids(size_t list_no) const {
    return il->get_ids(translate_list_no(this, list_no));
}

idx_t SliceInvertedLists::get_single_id(size_t list_no, size_t offset) const {
    return il->get_single_id(translate_list_no(this, list_no), offset);
}

void SliceInvertedLists::release_ids(size_t list_no, const idx_t* ids) const {
    return il->release_ids(translate_list_no(this, list_no), ids);
}

void SliceInvertedLists::prefetch_lists(const idx_t* list_nos, int nlist)
        const {
    std::vector<idx_t> translated_list_nos;
    for (int j = 0; j < nlist; j++) {
        idx_t list_no = list_nos[j];
        if (list_no < 0)
            continue;
        translated_list_nos.push_back(translate_list_no(this, list_no));
    }
    il->prefetch_lists(translated_list_nos.data(), translated_list_nos.size());
}

/*****************************************
 * VStackInvertedLists implementation
 ******************************************/

namespace {

// find the invlist this number belongs to
int translate_list_no(const VStackInvertedLists* vil, idx_t list_no) {
    FAISS_THROW_IF_NOT(list_no >= 0 && list_no < vil->nlist);
    int i0 = 0, i1 = vil->ils.size();
    const idx_t* cumsz = vil->cumsz.data();
    while (i0 + 1 < i1) {
        int imed = (i0 + i1) / 2;
        if (list_no >= cumsz[imed]) {
            i0 = imed;
        } else {
            i1 = imed;
        }
    }
    assert(list_no >= cumsz[i0] && list_no < cumsz[i0 + 1]);
    return i0;
}

idx_t sum_il_sizes(int nil, const InvertedLists** ils_in) {
    idx_t tot = 0;
    for (int i = 0; i < nil; i++) {
        tot += ils_in[i]->nlist;
    }
    return tot;
}

} // namespace

VStackInvertedLists::VStackInvertedLists(int nil, const InvertedLists** ils_in)
        : ReadOnlyInvertedLists(
                  sum_il_sizes(nil, ils_in),
                  nil > 0 ? ils_in[0]->code_size : 0) {
    FAISS_THROW_IF_NOT(nil > 0);
    cumsz.resize(nil + 1);
    for (int i = 0; i < nil; i++) {
        ils.push_back(ils_in[i]);
        FAISS_THROW_IF_NOT(ils_in[i]->code_size == code_size);
        cumsz[i + 1] = cumsz[i] + ils_in[i]->nlist;
    }
}

size_t VStackInvertedLists::list_size(size_t list_no) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->list_size(list_no);
}

const uint8_t* VStackInvertedLists::get_codes(size_t list_no) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->get_codes(list_no);
}

const uint8_t* VStackInvertedLists::get_single_code(
        size_t list_no,
        size_t offset) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->get_single_code(list_no, offset);
}

void VStackInvertedLists::release_codes(size_t list_no, const uint8_t* codes)
        const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->release_codes(list_no, codes);
}

const idx_t* VStackInvertedLists::get_ids(size_t list_no) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->get_ids(list_no);
}

idx_t VStackInvertedLists::get_single_id(size_t list_no, size_t offset) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->get_single_id(list_no, offset);
}

void VStackInvertedLists::release_ids(size_t list_no, const idx_t* ids) const {
    int i = translate_list_no(this, list_no);
    list_no -= cumsz[i];
    return ils[i]->release_ids(list_no, ids);
}

void VStackInvertedLists::prefetch_lists(const idx_t* list_nos, int nlist)
        const {
    std::vector<int> ilno(nlist, -1);
    std::vector<int> n_per_il(ils.size(), 0);
    for (int j = 0; j < nlist; j++) {
        idx_t list_no = list_nos[j];
        if (list_no < 0)
            continue;
        int i = ilno[j] = translate_list_no(this, list_no);
        n_per_il[i]++;
    }
    std::vector<int> cum_n_per_il(ils.size() + 1, 0);
    for (int j = 0; j < ils.size(); j++) {
        cum_n_per_il[j + 1] = cum_n_per_il[j] + n_per_il[j];
    }
    std::vector<idx_t> sorted_list_nos(cum_n_per_il.back());
    for (int j = 0; j < nlist; j++) {
        idx_t list_no = list_nos[j];
        if (list_no < 0)
            continue;
        int i = ilno[j];
        list_no -= cumsz[i];
        sorted_list_nos[cum_n_per_il[i]++] = list_no;
    }

    int i0 = 0;
    for (int j = 0; j < ils.size(); j++) {
        int i1 = i0 + n_per_il[j];
        if (i1 > i0) {
            ils[j]->prefetch_lists(sorted_list_nos.data() + i0, i1 - i0);
        }
        i0 = i1;
    }
}

/*****************************************
 * MaskedInvertedLists implementation
 ******************************************/

MaskedInvertedLists::MaskedInvertedLists(
        const InvertedLists* il0,
        const InvertedLists* il1)
        : ReadOnlyInvertedLists(il0->nlist, il0->code_size),
          il0(il0),
          il1(il1) {
    FAISS_THROW_IF_NOT(il1->nlist == nlist);
    FAISS_THROW_IF_NOT(il1->code_size == code_size);
}

size_t MaskedInvertedLists::list_size(size_t list_no) const {
    size_t sz = il0->list_size(list_no);
    return sz ? sz : il1->list_size(list_no);
}

const uint8_t* MaskedInvertedLists::get_codes(size_t list_no) const {
    size_t sz = il0->list_size(list_no);
    return (sz ? il0 : il1)->get_codes(list_no);
}

const idx_t* MaskedInvertedLists::get_ids(size_t list_no) const {
    size_t sz = il0->list_size(list_no);
    return (sz ? il0 : il1)->get_ids(list_no);
}

void MaskedInvertedLists::release_codes(size_t list_no, const uint8_t* codes)
        const {
    size_t sz = il0->list_size(list_no);
    (sz ? il0 : il1)->release_codes(list_no, codes);
}

void MaskedInvertedLists::release_ids(size_t list_no, const idx_t* ids) const {
    size_t sz = il0->list_size(list_no);
    (sz ? il0 : il1)->release_ids(list_no, ids);
}

idx_t MaskedInvertedLists::get_single_id(size_t list_no, size_t offset) const {
    size_t sz = il0->list_size(list_no);
    return (sz ? il0 : il1)->get_single_id(list_no, offset);
}

const uint8_t* MaskedInvertedLists::get_single_code(
        size_t list_no,
        size_t offset) const {
    size_t sz = il0->list_size(list_no);
    return (sz ? il0 : il1)->get_single_code(list_no, offset);
}

void MaskedInvertedLists::prefetch_lists(const idx_t* list_nos, int nlist)
        const {
    std::vector<idx_t> list0, list1;
    for (int i = 0; i < nlist; i++) {
        idx_t list_no = list_nos[i];
        if (list_no < 0)
            continue;
        size_t sz = il0->list_size(list_no);
        (sz ? list0 : list1).push_back(list_no);
    }
    il0->prefetch_lists(list0.data(), list0.size());
    il1->prefetch_lists(list1.data(), list1.size());
}

/*****************************************
 * MaskedInvertedLists implementation
 ******************************************/

StopWordsInvertedLists::StopWordsInvertedLists(
        const InvertedLists* il0,
        size_t maxsize)
        : ReadOnlyInvertedLists(il0->nlist, il0->code_size),
          il0(il0),
          maxsize(maxsize) {}

size_t StopWordsInvertedLists::list_size(size_t list_no) const {
    size_t sz = il0->list_size(list_no);
    return sz < maxsize ? sz : 0;
}

const uint8_t* StopWordsInvertedLists::get_codes(size_t list_no) const {
    return il0->list_size(list_no) < maxsize ? il0->get_codes(list_no)
                                             : nullptr;
}

const idx_t* StopWordsInvertedLists::get_ids(size_t list_no) const {
    return il0->list_size(list_no) < maxsize ? il0->get_ids(list_no) : nullptr;
}

void StopWordsInvertedLists::release_codes(size_t list_no, const uint8_t* codes)
        const {
    if (il0->list_size(list_no) < maxsize) {
        il0->release_codes(list_no, codes);
    }
}

void StopWordsInvertedLists::release_ids(size_t list_no, const idx_t* ids)
        const {
    if (il0->list_size(list_no) < maxsize) {
        il0->release_ids(list_no, ids);
    }
}

idx_t StopWordsInvertedLists::get_single_id(size_t list_no, size_t offset)
        const {
    FAISS_THROW_IF_NOT(il0->list_size(list_no) < maxsize);
    return il0->get_single_id(list_no, offset);
}

const uint8_t* StopWordsInvertedLists::get_single_code(
        size_t list_no,
        size_t offset) const {
    FAISS_THROW_IF_NOT(il0->list_size(list_no) < maxsize);
    return il0->get_single_code(list_no, offset);
}

void StopWordsInvertedLists::prefetch_lists(const idx_t* list_nos, int nlist)
        const {
    std::vector<idx_t> list0;
    for (int i = 0; i < nlist; i++) {
        idx_t list_no = list_nos[i];
        if (list_no < 0)
            continue;
        if (il0->list_size(list_no) < maxsize) {
            list0.push_back(list_no);
        }
    }
    il0->prefetch_lists(list0.data(), list0.size());
}

} // namespace faiss
