Oh, Numerical Recipes is nice but their algorithm implementations are not really state-of-the-art. I highly recommend using FFTW (https://fftw.org/ https://fftw

Oh, Numerical Recipes is nice but their algorithm implementations are not really state-of-the-art. I highly recommend using FFTW (https://fftw.org/ https://fftw.org/) as it will likely give you a substantial performance improvement.