annotate src/vamp-sdk/FFTimpl.cpp @ 354:e85513153c71

Initialise rate to 0. Otherwise there's a danger plugins will change the SampleType (e.g. to VariableSampleRate) but not set the rate because they don't think they need it (when in fact it needs to be set to 0)

/* Public domain FFT implementation from Don Cross. */

static void
fft(unsigned int n, bool inverse,
    const double *ri, const double *ii,
    double *ro, double *io)
{
    if (!ri || !ro || !io) return;

    unsigned int bits;
    unsigned int i, j, k, m;
    unsigned int blockSize, blockEnd;

    double tr, ti;

    if (n < 2) return;
    if (n & (n-1)) return;

    double angle = 2.0 * M_PI;
    if (inverse) angle = -angle;

    for (i = 0; ; ++i) {
	if (n & (1 << i)) {
	    bits = i;
	    break;
	}
    }

#ifdef _MSC_VER
    int *table = (int *)_malloca(n * sizeof(int));
#else
    int table[n];
#endif

    for (i = 0; i < n; ++i) {
        m = i;
        for (j = k = 0; j < bits; ++j) {
            k = (k << 1) | (m & 1);
            m >>= 1;
        }
        table[i] = k;
    }

    if (ii) {
	for (i = 0; i < n; ++i) {
	    ro[table[i]] = ri[i];
	    io[table[i]] = ii[i];
	}
    } else {
	for (i = 0; i < n; ++i) {
	    ro[table[i]] = ri[i];
	    io[table[i]] = 0.0;
	}
    }

    blockEnd = 1;

    for (blockSize = 2; blockSize <= n; blockSize <<= 1) {

	double delta = angle / (double)blockSize;
	double sm2 = -sin(-2 * delta);
	double sm1 = -sin(-delta);
	double cm2 = cos(-2 * delta);
	double cm1 = cos(-delta);
	double w = 2 * cm1;
	double ar[3], ai[3];

	for (i = 0; i < n; i += blockSize) {

	    ar[2] = cm2;
	    ar[1] = cm1;

	    ai[2] = sm2;
	    ai[1] = sm1;

	    for (j = i, m = 0; m < blockEnd; j++, m++) {

		ar[0] = w * ar[1] - ar[2];
		ar[2] = ar[1];
		ar[1] = ar[0];

		ai[0] = w * ai[1] - ai[2];
		ai[2] = ai[1];
		ai[1] = ai[0];

		k = j + blockEnd;
		tr = ar[0] * ro[k] - ai[0] * io[k];
		ti = ar[0] * io[k] + ai[0] * ro[k];

		ro[k] = ro[j] - tr;
		io[k] = io[j] - ti;

		ro[j] += tr;
		io[j] += ti;
	    }
	}

	blockEnd = blockSize;
    }

    if (inverse) {

	double denom = (double)n;

	for (i = 0; i < n; i++) {
	    ro[i] /= denom;
	    io[i] /= denom;
	}
    }

#ifdef _MSC_VER
    _freea(table);
#endif
}