Lisp Fourier Transform Library Faster Yet (v1.3) October 13th, 2009
Patrick Stein

I released version 1.3 of my Common Lisp Fourier Transform library today. It is significantly faster than yesterday’s version. On my MacBook Pro in SBCL 1.0.30 with a 512 by 512 by 16 array, version 1.3 takes 3.74 seconds where version 1.2 took 9.77 seconds and version 1.0 took 25.31 seconds. For a breakdown of performance on various array sizes with various Lisp implementations, see the performance section of the library page.

Most of the speed improvement in this version came from memory improvements. Version 1.3 doesn’t cons at all in SBCL during the processing of each row. Version 1.2 inadvertently consed three rows worth of complex numbers for every row transformed.

My library is still about 25% slower than Bordeaux FFT for one-dimensional arrays. My library, however, has full support for multi-dimensional arrays where Bordeaux-FFT does not.

I also included some validation test cases using NST to this release. To try them, go to the library directory, hop in your Lisp, and load regression.lisp.