Why does my finite state machine take so long to execute?

Posted by BillyONeal on Stack Overflow See other posts from Stack Overflow or by BillyONeal
Published on 2010-03-19T02:00:16Z Indexed on 2010/03/19 2:01 UTC
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Hello all :)

I'm working on a state machine which is supposed to extract function calls of the form

/* I am a comment */
//I am a comment
perf("this.is.a.string.which\"can have QUOTES\"", 123456);

where the extracted data would be perf("this.is.a.string.which\"can have QUOTES\"", 123456); from a file. Currently, to process a 41kb file, this process is taking close to a minute and a half. Is there something I'm seriously misunderstanding here about this finite state machine?

#include <boost/algorithm/string.hpp>
std::vector<std::string> Foo()
{
    std::string fileData;
    //Fill filedata with the contents of a file
    std::vector<std::string> results;
    std::string::iterator begin = fileData.begin();
    std::string::iterator end = fileData.end();
    std::string::iterator stateZeroFoundLocation = fileData.begin();
    std::size_t state = 0;
    for(; begin < end; begin++)
    {
        switch (state)
        {
        case 0:
            if (boost::starts_with(boost::make_iterator_range(begin, end), "pref(")) {
                stateZeroFoundLocation = begin;
                begin += 4;
                state = 2;
            } else if (*begin == '/')
                state = 1;
            break;
        case 1:
            state = 0;
            switch (*begin)
            {
            case '*':
                begin = boost::find_first(boost::make_iterator_range(begin, end), "*/").end();
                break;
            case '/':
                begin = std::find(begin, end, L'\n');
            }
            break;
        case 2:
            if (*begin == '"')
                state = 3;
            break;
        case 3:
            switch(*begin)
            {
            case '\\':
                state = 4;
                break;
            case '"':
                state = 5;
            }
            break;
        case 4:
            state = 3;
            break;
        case 5:
            if (*begin == ',')
                state = 6;
            break;
        case 6:
            if (*begin != ' ')
                state = 7;
            break;
        case 7:
            switch(*begin)
            {
            case '"':
                state = 8;
                break;
            default:
                state = 10;
                break;
            }
            break;
        case 8:
            switch(*begin)
            {
            case '\\':
                state = 9;
                break;
            case '"':
                state = 10;
            }
            break;
        case 9:
            state = 8;
            break;
        case 10:
            if (*begin == ')')
                state = 11;
            break;
        case 11:
            if (*begin == ';')
                state = 12;
            break;
        case 12:
            state = 0;
            results.push_back(std::string(stateZeroFoundLocation, begin));
        };
    }
    return results;
}

Billy3

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