Method createMicroCode

runtime/Log.cc:815–968

* Generate a more efficient internal representation describing how to process * the compressed arguments of a NANO_LOG statement given its static * log information. * * The output representation would look something like a FormatMetadata with * nested PrintFragments. This representation can then be interpreted by the * state machine in decompressNextLogStatement to decompress the log stateme

 *      true indicates success; false indicates malformed printf format string
 */
bool
Log::Decoder::createMicroCode(char **microCode,
                                const char *formatString,
                                const char *filename,
                                uint32_t linenum,
                                uint8_t severity)
{
    using namespace NanoLogInternal::Log;

    size_t formatStringLength = strlen(formatString) + 1; // +1 for NULL
    char *microCodeStartingPos = *microCode;
    FormatMetadata *fm = reinterpret_cast<FormatMetadata*>(*microCode);
    *microCode += sizeof(FormatMetadata);

    fm->logLevel = severity;
    fm->lineNumber = linenum;
    fm->filenameLength = static_cast<uint16_t>(strlen(filename) + 1);
    *microCode = stpcpy(*microCode, filename) + 1;

    fm->numNibbles = 0;
    fm->numPrintFragments = 0;

    std::regex regex("^%"
                     "([-+ #0]+)?" // Flags (Position 1)
                     "([\\d]+|\\*)?" // Width (Position 2)
                     "(\\.(\\d+|\\*))?"// Precision (Position 4; 3 includes '.')
                     "(hh|h|l|ll|j|z|Z|t|L)?" // Length (Position 5)
                     "([diuoxXfFeEgGaAcspn])"// Specifier (Position 6)
                     );

    size_t i = 0;
    std::cmatch match;
    int consecutivePercents = 0;
    size_t startOfNextFragment = 0;
    PrintFragment *pf = nullptr;

    // The key idea here is to split up the format string in to fragments (i.e.
    // PrintFragments) such that there is at most one specifier per fragment.
    // This then allows the decompressor later to consume one argument at a
    // time and print the fragment (vs. buffering all the arguments first).

    while (i < formatStringLength) {
        char c = formatString[i];

        // Skip the next character if there's an escape
        if (c == '\\') {
            i += 2;
            continue;
        }

        if (c != '%') {
            ++i;
            consecutivePercents = 0;
            continue;
        }

        // If there's an even number of '%'s, then it's a comment
        if (++consecutivePercents % 2 == 0