Function cpu_statevec_packAmpsIntoBuffer

quest/src/cpu/cpu_subroutines.cpp:220–248

template <int NumQubits>
qindex cpu_statevec_packAmpsIntoBuffer(Qureg qureg, vector<int> qubitInds, vector<int> qubitStates) {

    assert_numQubitsMatchesQubitStatesAndTemplateParam(qubitInds.size(), qubitStates.size(), NumQubits);

    // each control qubit halves the needed iterations
    qindex numIts = qureg.numAmpsPerNode / powerOf2(qubitInds.size());

    // amplitudes are packed at an offset into the buffer
    qindex offset = getSubBufferSendInd(qureg);

    auto sortedQubitInds = util_getSorted(qubitInds);
    auto qubitStateMask  = util_getBitMask(qubitInds, qubitStates);
    
    // use template param to compile-time unroll loop in insertBits()
    SET_VAR_AT_COMPILE_TIME(int, numBits, NumQubits, qubitInds.size());

    #pragma omp parallel for if(qureg.isMultithreaded)
    for (qindex n=0; n<numIts; n++) {

        // i = nth local index where qubits are in specified states
        qindex i = insertBitsWithMaskedValues(n, sortedQubitInds.data(), numBits, qubitStateMask);

        // pack the potentially-strided amplitudes into a contiguous sub-buffer
        qureg.cpuCommBuffer[offset + n] = qureg.cpuAmps[i];
    }

    // return the number of packed amps
    return numIts;
}


qindex cpu_statevec_packPairSummedAmpsIntoBuffer(Qureg qureg, int qubit1, int qubit2, int qubit3, int bit2) {