diff --git a/run-tests.py b/run-tests.py
index 3c44571..634b0b6 100644
--- a/run-tests.py
+++ b/run-tests.py
@@ -16,10 +16,32 @@ def perm_ryser(a):
     terms=map(get_term, indeces) 
     return np.sum(terms)*((-1)**n)
 
-dimension=2
-real=np.ones((dimension, dimension))
-imag=np.ones((dimension, dimension))*0
+def explain_ryser(a):
+    ''' the permanent calculated using the ryser formula. much faster than the naive approach '''
+    n,n2=a.shape
+    z=np.arange(n)
+    irange=xrange(2**n)
+    get_index=lambda i: (i & (1 << z)) != 0 
+    for q in irange:
+        print get_index(q)
+    #get_term=lambda index: ((-1)**np.sum(index))*np.prod(np.sum(a[index,:], 0))
+    #indeces=map(get_index, irange)
+    #terms=map(get_term, indeces) 
+    #return np.sum(terms)*((-1)**n)
+
+
+
+dimension=5
+real=np.random.uniform(-1, 1, dimension*dimension).reshape((dimension, dimension))
+imag=np.random.uniform(-1, 1, dimension*dimension).reshape((dimension, dimension))
 submatrix=real+1j*imag
-submatrix[0,0]*=2
-print lib.permanent(submatrix)
-print perm_ryser(submatrix)
+
+t=time.clock()
+for i in range(1000):
+    perm_ryser(submatrix)
+print time.clock()-t
+
+t=time.clock()
+for i in range(1000):
+    lib.permanent(submatrix)
+print time.clock()-t
diff --git a/src/permanent.c b/src/permanent.c
index 58149d8..e97452d 100644
--- a/src/permanent.c
+++ b/src/permanent.c
@@ -9,6 +9,21 @@
                     (x1) * PyArray_STRIDES(submatrix)[1])))
 #define SM_shape(x0) (int) PyArray_DIM(submatrix, x0)
 
+int countbits(unsigned int n) 
+{
+    int q=n;
+    q = (q & 0x5555555555555555) + ((q & 0xAAAAAAAAAAAAAAAA) >> 1);
+    q = (q & 0x3333333333333333) + ((q & 0xCCCCCCCCCCCCCCCC) >> 2);
+    q = (q & 0x0F0F0F0F0F0F0F0F) + ((q & 0xF0F0F0F0F0F0F0F0) >> 4);
+    q = (q & 0x00FF00FF00FF00FF) + ((q & 0xFF00FF00FF00FF00) >> 8);
+    q = (q & 0x0000FFFF0000FFFF) + ((q & 0xFFFF0000FFFF0000) >> 16);
+    q = (q & 0x00000000FFFFFFFF) + ((q & 0xFFFFFFFF00000000) >> 32); // This last & isq't strictly qecessary.
+    return q;
+}
+
+int bitparity (unsigned int n) { return 1 - (countbits(n) & 1)*2; }
+
+
 // Complex numbers
 static const npy_complex128 complex_one = {.real=1, .imag=0};
 static const npy_complex128 complex_zero = {.real=0, .imag=0};
@@ -20,8 +35,8 @@ static npy_complex128 complex_add(npy_complex128 a, npy_complex128 b) {
 }
 static npy_complex128 complex_prod(npy_complex128 a, npy_complex128 b) { 
     npy_complex128 x;
-    x.real = a.real*b.real+a.imag*b.imag;
-    x.imag = a.real*b.imag+a.imag*b.real;
+    x.real = a.real*b.real - a.imag*b.imag;
+    x.imag = a.imag*b.real + a.real*b.imag;
     return x;
 }
 
@@ -36,46 +51,28 @@ PyMODINIT_FUNC initpermanent(void) {                            // Module initia
   import_array();
 }
 
-inline int* dec2binarr(long n, int dim)
-{
-    // note: res[dim] will save the sum res[0]+...+res[dim-1]
-    int* res = (int*)calloc(dim + 1, sizeof(int));   
-    int pos = dim - 1;
-    // note: this will crash if dim < log_2(n)...
-    while (n > 0)
-    {
-        res[pos] = n % 2;
-        res[dim] += res[pos];
-        n = n / 2; // integer division        
-        pos--;
-    }
-    return res;
-}
-
 // Ryser's algorithm 
 static npy_complex128 perm_ryser(PyArrayObject *submatrix) {
     int n = (int) PyArray_DIM(submatrix, 0);
-    int i = 0; int z = 0; int y = 0;
-    npy_complex128 sum, prod;
+    npy_complex128 rowsum, rowsumprod;
     npy_complex128 perm = complex_zero;
     int exp = 1 << n; 
+    int i, y, z;
 
     // Iterate over exponentially many index strings
     for (i=0; i<exp; ++i) {
-        prod = complex_one;
+        rowsumprod = complex_one;
         for (y=0; y<n; ++y) {               // Rows
-            sum = complex_zero;
+            rowsum = complex_zero;
             for (z=0; z<n; ++z) {           // Columns
-                if ((i && (1 << z)) != 0) { 
-                    sum = complex_add(sum, SM(z,y)); 
-                }
+                if ((i & (1 << z)) != 0) { rowsum = complex_add(rowsum, SM(z,y)); }
             }
-            prod = complex_prod(prod, sum);
+            rowsumprod = complex_prod(rowsumprod, rowsum);
         }
-        if (i%2 == 1) {prod.real*=-1; prod.imag*=-1;}
-        perm = complex_add(perm, prod);
+        int sign = bitparity(i); 
+        perm.real+=sign*rowsumprod.real; perm.imag+=sign*rowsumprod.imag;
     }
-    if (i%2 == 1) {perm.real*=-1; perm.imag*=-1;}
+    if (n%2 == 1) {perm.real*=-1; perm.imag*=-1;}
     return perm;
 }