Function isPauliStrSumCoeffWithinQcompRange

quest/src/core/parser.cpp:355–393

bool isPauliStrSumCoeffWithinQcompRange(string line) {

    // it is gauranteed that line is interpretable and contains a regex-matching
    // coefficient, but we must additionally verify it is within range of qreal.
    // So we duck type each of the 1 or 2 matches with the real regex (i.e. one or 
    // both of the real and imaginary components of a complex coeff).

    // process only the coeff, since pauli codes may resemble coeffs (e.g. 1)
    string coeff, _; 
    separateStringIntoCoeffAndPaulis(line, coeff, _); // discard pauli substr

    // beautiful iterator boilerplate
    sregex_iterator it(coeff.begin(), coeff.end(), regexes::real);
    sregex_iterator end;

    // valid coeffs contain 1 or 2 reals, never 0
    if (it == end)
        return false;

    // enumerate all matches of 'real' regex in line
    for (; it != end; it++) {

        // remove whitespace (stold cannot handle space between sign and number)
        string match = it->str(0);
        removeWhiteSpace(match);

        // return false if number cannot become a qreal
        try {
            precisionAgnosticStringToFloat(match);
        } catch (const out_of_range&) {
            return false;
        } catch (const invalid_argument&) { // should be impossible (indicates bad regex)
            return false;
        }
    }

    // report that each double in coeff substr was parsable
    return true;
}


void assertStringIsValidPauliStrSum(string lines, const char* caller) {