Function paulis_getKeyOfSameMixedAmpsGroup

quest/src/core/paulilogic.cpp:229–247

PAULI_MASK_TYPE paulis_getKeyOfSameMixedAmpsGroup(PauliStr str) {

    PAULI_MASK_TYPE key = 0;

    // in theory, we can reduce the number of involved operations by bit-shifting
    // str left by 1, XOR'ing this with str, and retaining every 2nd bit, producing
    // e.g. key=0110 from str=IXYZ. However, this is an insignificant speedup which
    // risks sneaky bugs related to handling str's two masks.

    int maxInd = paulis_getIndOfLefmostNonIdentityPauli(str);

    for (int i=0; i<=maxInd; i++) {
        int pauli = paulis_getPauliAt(str, i);
        int isXY = (pauli == 1 || pauli == 2);
        key |= (isXY << i);
    }

    return key;
}


std::pair<qcomp,PauliStr> paulis_getPauliStrProd(PauliStr strA, PauliStr strB) {