gnu: Add kiss-fft-for-extempore.

* gnu/packages/algebra.scm (kiss-fft-for-extempore): New variable.

gnu/packages/algebra.scm

@@ -505,6 +505,30 @@ syntax is similar to that of C, so basic usage is familiar.  It also includes
 \"dc\", a reverse-polish calculator.")
     (license license:gpl2+)))
 
+;; The original kiss-fft does not have a complete build system and does not
+;; build any shared libraries.  This is a fork used by Extempore.
+(define-public kiss-fft-for-extempore
+  (package
+    (name "kiss-fft-for-extempore")
+    (version "1.3.0")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "https://github.com/extemporelang/kiss_fft/archive/"
+                                  version ".tar.gz"))
+              (file-name (string-append name "-" version ".tar.gz"))
+              (sha256
+               (base32
+                "0hkp9l6l4c92fb1l2sh6a6zv1hynpvb2s4d03vd8vxyvybc0l4pv"))))
+    (build-system cmake-build-system)
+    (arguments `(#:tests? #f)) ; no tests included
+    (home-page "https://github.com/extemporelang/kiss_fft")
+    (synopsis "Mixed-radix Fast Fourier Transform")
+    (description
+     "Kiss FFT attempts to be a reasonably efficient, moderately useful FFT
+that can use fixed or floating data types and can easily be incorporated into
+a C program.")
+    (license license:bsd-3)))
+
 (define-public fftw
   (package
     (name "fftw")