Interpreting C++ autocorrelation code

I found this autocorrelation code, but I simply don't know what is "float_vec_t", for example. Is it a class or something? (I am trying to translate it to Action-script or JavaScript, which I know well)

class LPCAnalysis{
    public:
      float_vec_t LPCAnalysis::autoCorrelation(const float_vec_t &x);

};


/* Calculate the (UN-normalized) autocorrelation for a frame of a
signal   */

float_vec_t LPCAnalysis::autoCorrelation(const float_vec_t &x)
{
    short order=x.size();

    float_vec_t R(order);
    float sum;
    int i,j;

    for (i=0;i<order;i++) {
        sum=0;
        for (j=0;j<order-i;j++) {
            sum+=x[j]*x[j+i];
        }
        R[i]=sum;
    }
    return R;
}

below is my progress so far:

function LPCAnalysis (x:Array) {

    var order:int = x.length

    var R:Array= []
    var sum:Number
    var i:int
    var j:int

    for (i=0;i<order;i++) {
        sum = 0
        for (j=0;j<order-i;j++) {
            sum+=x[j]*x[j+i]
        }
        R[i] = sum
    }
    return R

}

Also, how can I extract the final frequency from the array R? (if R is an array). And what are the parameters that I should give to the function? An FFT result, a microphone signal?