diff --git a/bitvector.h b/bitvector.h
index 28f9820..1d2923b 100644
--- a/bitvector.h
+++ b/bitvector.h
@@ -93,6 +93,24 @@ r.clear();
 for(int i=0; i<n; ++i) if(v[i]) r[i]=1;
 }
 
+//mantissa of a floating number between 0 and 1
+template <typename T>
+bitvector mantissa(const T &x, int nbits)
+{
+if(x<0||x>=1) laerror("number not normalized in bitvector mantissa");
+bitvector b(nbits);
+b.clear();
+T y= x+x;
+for(int i=0; i<nbits; ++i)
+	{
+	int n= (int) y;
+	if(n&1) b.set(i);
+	y += y;
+	}
+return b;
+}
+
+
 template <typename T>
 void bitvector_compress(bitvector &r, const NRVec<T> &v)
 {
diff --git a/t.cc b/t.cc
index 18738e3..2e4e7fd 100644
--- a/t.cc
+++ b/t.cc
@@ -2574,7 +2574,7 @@ cout <<test;
 cout <<"Error = "<<(expitszsz-test).norm()<<endl;
 }
 
-if(1)
+if(0)
 {
 NRVec<double> x({1,2,3});
 NRVec<double> y({4,5,6});
@@ -2585,4 +2585,11 @@ x.concatme(y);
 cout <<x;
 }
 
+if(1)
+{
+double x;
+cin>>x;
+cout <<mantissa(x,20)<<endl;
+}
+
 }