fft size selector

fftsize.cpp

// pick a good fft size for fftw (of the form 2^a * 3^b * 5^c * 7^d * [1|11|13] )
int selectFFTSize(int n)
{
	int s = 1;

	for(int ef : {1, 11, 13}) {
		for(int d = 1 ; d <= n; d *= 7) {
			for(int c = 1; c <= n; c *= 5) {
				for(int b = 1; b <= n; b *= 3) {
					for(int a = 1; a <= n; a *= 2) {
						int t = a * b * c * d * ef;
						if(t > n) {
							break;
						}
						s = std::max(s, t);
					}
				}
			}
		}
	}

	return s;
}

fftsizeFromSpectrumSize.cpp

int fftsize = selectFFTSize(2 * (desiredSpectrumSize - 1));
int actualSpectrumSize = static_cast<int>(floor(fftsize / 2)) + 1;