Function AllToAll

library/cpp/netliba/v6/ib_collective.cpp:184–280

        AA_POW2_MERGE,
    };
    static int AllToAll(TMergePlan* plan, int iter, int sl, EAllToAllMode mode, const TVector<int>& myGroup, TVector<TCoverInterval>* cover) {
        TVector<TCoverInterval>& hostCoverage = *cover;
        int groupSize = myGroup.ysize();

        for (int k = 1; k < groupSize; ++k) {
            int h1 = myGroup[k - 1];
            int h2 = myGroup[k];
            Y_ABORT_UNLESS(hostCoverage[h1].Fin == hostCoverage[h2].Beg, "Invalid host order in CreateGroupMerge()");
        }

        switch (mode) {
            case AA_POW2: {
                for (int delta = 1; delta < groupSize; delta *= 2) {
                    int sz = Min(delta, groupSize - delta);
                    for (int offset = 0; offset < groupSize; ++offset) {
                        int srcRank = myGroup[offset];
                        int dstRank = myGroup[(offset + delta) % groupSize];

                        int start = offset + 1 - sz;
                        int finish = offset + 1;
                        if (start < 0) {
                            // [start; myGroup.size())
                            int dataBeg = hostCoverage[myGroup[start + groupSize]].Beg;
                            int dataFin = hostCoverage[myGroup.back()].Fin;
                            plan->Transfer(iter, srcRank, dstRank, sl, dataBeg, dataFin);
                            // [0; finish)
                            dataBeg = hostCoverage[myGroup[0]].Beg;
                            dataFin = hostCoverage[myGroup[finish - 1]].Fin;
                            plan->Transfer(iter, srcRank, dstRank, sl, dataBeg, dataFin);
                        } else {
                            // [start;finish)
                            int dataBeg = hostCoverage[myGroup[start]].Beg;
                            int dataFin = hostCoverage[myGroup[finish - 1]].Fin;
                            plan->Transfer(iter, srcRank, dstRank, sl, dataBeg, dataFin);
                        }
                    }
                    ++iter;
                }
            } break;
            case AA_CIRCLE: {
                for (int dataDelta = 1; dataDelta < groupSize; ++dataDelta) {
                    for (int offset = 0; offset < groupSize; ++offset) {
                        int srcRank = myGroup[offset];
                        int dstRank = myGroup[(offset + 1) % groupSize];

                        int dataRank = myGroup[(offset + 1 - dataDelta + groupSize) % groupSize];
                        int dataBeg = hostCoverage[dataRank].Beg;
                        int dataFin = hostCoverage[dataRank].Fin;

                        plan->Transfer(iter, srcRank, dstRank, sl, dataBeg, dataFin);
                    }
                    ++iter;
                }
            } break;
            case AA_STAR: {
                for (int offset = 0; offset < groupSize; ++offset) {
                    for (int delta = 1; delta < groupSize; ++delta) {
                        int srcRank = myGroup[offset];