Speedup of arcLength

By my tests, this version of cv::arcLength is almost 10% faster than the
one using a buffer it replaces.

modules/imgproc/src/shapedescr.cpp

@@ -301,9 +301,7 @@ double cv::arcLength( InputArray _curve, bool is_closed )
     CV_Assert( count >= 0 && (depth == CV_32F || depth == CV_32S));
     double perimeter = 0;
 
-    int i, j = 0;
-    const int N = 16;
-    float buf[N];
+    int i;
 
     if( count <= 1 )
         return 0.;
@@ -319,15 +317,8 @@ double cv::arcLength( InputArray _curve, bool is_closed )
     {
         Point2f p = is_float ? ptf[i] : Point2f((float)pti[i].x,(float)pti[i].y);
         float dx = p.x - prev.x, dy = p.y - prev.y;
-        buf[j] = dx*dx + dy*dy;
+        perimeter += sqrtf(dx*dx + dy*dy);
 
-        if( ++j == N || i == count-1 )
-        {
-            Mat bufmat(1, j, CV_32F, buf);
-            sqrt(bufmat, bufmat);
-            for( ; j > 0; j-- )
-                perimeter += buf[j-1];
-        }
         prev = p;
     }