function execution time

if a function is taking longer to execute every time it is called, what could that imply?

alright I'm not getting anywhere. Heres the offending code, for some reason when it hits the return it takes about twice as long as the previous time to execute. I don't think it is a memory leak as this code and the function that calls it aren't concerned with memory allocation (but what do I know)

std::vector<std::vector<Segment> > Environment::_AIScopeSubArray(int yPos, int xPos, int AIScope)
{
    std::vector<std::vector<Segment> > subScope;
    int scopeRad = AIScope/2;

    subScope.resize(AIScope);
    for(int idx = 0; idx < AIScope; idx++)
        subScope[idx].resize(AIScope);

    for(int idx = 0; idx < AIScope; idx++)
        for(int jdx = 0; jdx < AIScope; jdx++)
        {
            if((idx+(yPos-scopeRad) >= 0) && (idx+(yPos-scopeRad) < GRIDSIZE) && (jdx+(xPos-scopeRad) >= 0) && (jdx+(xPos-scopeRad) < GRIDSIZE))
            {
                subScope[idx][jdx] = grid_[idx+(yPos-scopeRad)][jdx+(xPos-scopeRad)];
            }
            else
            {
                subScope[idx][jdx].setOOB(true);
            }
        }
        return subScope;
}

This is supposed to return a small portion of a larger grid, to act as a field of vision for some monsters