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package jm.audio.math;

/**
 * Supplies static methods for factoring integers needed by various FFT classes.
 *
 * @author Bruce R. Miller [email protected]
 * @author Contribution of the National Institute of Standards and Technology,
 * @author not subject to copyright.
 * @author Derived from GSL (Gnu Scientific Library)
 * @author GSL's FFT Code by Brian Gough [email protected]
 * @author Since GSL is released under
 * @author GPL,
 * @author this package must also be.
 */
public class Factorize {

    /**
     * Return the prime factors of n.
     * The method first extracts any factors in fromfactors, in order (which
     * needn't actually be prime).  Remaining factors in increasing order follow.
     */
    public static int[] factor(int n, int fromfactors[]) {
        int factors[] = new int[64]; // Can't be more than 64 factors.
        int nf = 0;
        int ntest = n;
        int factor;

        if (n <= 0)            // Error case
            throw new Error("Number (" + n + ") must be positive integer");

    /* deal with the preferred factors first */
        for (int i = 0; i < fromfactors.length && ntest != 1; i++) {
            factor = fromfactors[i];
            while ((ntest % factor) == 0) {
                ntest /= factor;
                factors[nf++] = factor;
            }
        }

    /* deal with any other even prime factors (there is only one) */
        factor = 2;
        while ((ntest % factor) == 0 && (ntest != 1)) {
            ntest /= factor;
            factors[nf++] = factor;
        }

    /* deal with any other odd prime factors */
        factor = 3;
        while (ntest != 1) {
            while ((ntest % factor) != 0) {
                factor += 2;
            }
            ntest /= factor;
            factors[nf++] = factor;
        }

    /* check that the factorization is correct */
        int product = 1;
        for (int i = 0; i < nf; i++) {
            product *= factors[i];
        }
        if (product != n)
            throw new Error("factorization failed for " + n);

    /* Now, make an array of the right length containing the factors... */
        int f[] = new int[nf];
        System.arraycopy(factors, 0, f, 0, nf);
        return f;
    }

    /**
     * Return the integer log, base 2, of n, or -1 if n is not an integral power of 2.
     */
    public static int log2(int n) {
        int log = 0;

        for (int k = 1; k < n; k *= 2, log++) ;

        if (n != (1 << log))
            return -1; /* n is not a power of 2 */
        return log;
    }
}