diff --git a/fft.py b/fft.py
index 675a648..5fc4ae2 100644
--- a/fft.py
+++ b/fft.py
@@ -4,21 +4,18 @@ pi=math.pi
 e=math.e
 j=complex(0,1)
 
-def T(n,k):
-    return e ** -2*j*pi*k/n
-
 def fft(f):
     n=len(f)
     if n==1:
         return f
 
-    for p in 4,3,2,5:
+    for p in 2,3,5:
         if n%p==0:
             break
     else:
         raise Exception('%s not factorable ' % n)
-    m = n/p
 
+    m = n/p
     Fm=[]
     for q in range(p): # 0,1
         fp = f[q::p]
@@ -29,9 +26,17 @@ def fft(f):
     for k in range(n):
         val = 0
         for q in range(p):
-            t = e ** ( -j*2*pi*k*q/n )
+            t = e ** ( j*2*pi*k*q/n )
             val += Fm[ q*m + (k%m) ] * t
         Fout[k] = val
 
     return Fout
 
+def test(f=range(256),ntimes=10):
+    import time
+    t0 = time.time()
+    for i in range(ntimes):
+        fft(f)
+    t1 = time.time()
+    print '%ss'% (t1-t0)
+