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changeset 429:2fbf3ce1e08b

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Cache the factorials, makes things slightly quicker
author Chris Cannam
date Tue, 08 Oct 2013 07:57:27 +0100
parents 9e3e97ecf9d0
children 7ee8c2d55e58
files src/may/signal/window.yeti
diffstat 1 files changed, 10 insertions(+), 7 deletions(-) [+]
line wrap: on
line diff
--- a/src/may/signal/window.yeti	Sat Oct 05 11:29:39 2013 +0100
+++ b/src/may/signal/window.yeti	Tue Oct 08 07:57:27 2013 +0100
@@ -100,16 +100,19 @@
 
 //!!! if kaiser is going to take a structure, so I guess should sinc and cosineWindow
 kaiser { length, beta } =
-   (bes0 x = 
-       (fact x = fold do x y: x*y done 1 [1..x];   // x!
-        ipow a b = fold do x _: x*a done 1 [1..b]; // a^b where b∈ℕ
-        square x = x*x;
-        term x i =
+   (terms = 20;
+    fact x = fold do x y: x*y done 1 [1..x];   // x!
+    ipow a b = fold do x _: x*a done 1 [1..b]; // a^b where b∈ℕ
+    factorials = array (map fact [1..terms]);
+    bes0 x = 
+       (term x i =
             case i of
              0: 1;
-             _: (ipow (x/2) (i*2)) / (square (fact i));
+             _:
+                 f = factorials[i-1];
+                 (ipow (x/2) (i*2)) / (f * f);
             esac;
-        sum (map (term x) [0..20]));
+        sum (map (term x) [0..terms]));
     denominator = bes0 beta;
     kw = vec.fromList
        (map do i: