From 206d4f851dac8e55d04f55b502f9dc0c30ea24ab Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Wed, 8 Aug 2012 21:00:49 -0700
Subject: [PATCH] math.transforms.fft: adding cross-correlation.

---
 extra/math/transforms/fft/fft-tests.factor | 5 +++++
 extra/math/transforms/fft/fft.factor       | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/extra/math/transforms/fft/fft-tests.factor b/extra/math/transforms/fft/fft-tests.factor
index fdfeab5f7a..8435adc3e3 100644
--- a/extra/math/transforms/fft/fft-tests.factor
+++ b/extra/math/transforms/fft/fft-tests.factor
@@ -24,3 +24,8 @@ IN: math.transforms.fft
     { C{ 1+2/3 0 } C{ -1/3 0 } C{ -1/3 0 } }
     { 1 2 2 } ifft 1e-12 v~
 ] unit-test
+
+{ t } [
+    { C{ 0.05 0.0 } C{ 0.05 0.0 } C{ 0.05 0.0 } C{ 0.05 0.0 } }
+    { 0.1 0.1 0.1 0.1 } { 0.2 0.1 0.1 0.1 } correlate 1e-12 v~
+] unit-test
diff --git a/extra/math/transforms/fft/fft.factor b/extra/math/transforms/fft/fft.factor
index 16c202bd3b..9cce31d92f 100644
--- a/extra/math/transforms/fft/fft.factor
+++ b/extra/math/transforms/fft/fft.factor
@@ -41,3 +41,6 @@ ERROR: not-enough-data ;
     [ not-enough-data ] [
         t over length even? [ (fft) ] [ (slow-fft) ] if
     ] if-empty ;
+
+: correlate ( x y -- z )
+    [ fft ] [ reverse fft ] bi* v* ifft ;