--- a/scripts/general/accumarray.m
+++ b/scripts/general/accumarray.m
@@ -1,4 +1,5 @@
 ## Copyright (C) 2007, 2008, 2009 David Bateman
+## Copyright (C) 2009 VZLU Prague
 ##
 ## This file is part of Octave.
 ##
@@ -64,20 +65,6 @@
   endif
   ndims = size (subs, 2);
 
-  if (nargin < 3 || isempty (sz))
-    sz = max (subs);
-    if (isscalar(sz))
-      sz = [sz, 1];
-    endif
-  elseif (length (sz) != ndims
-	  && (ndims != 1 || length (sz) != 2 || sz(2) != 1))
-    error ("accumarray: inconsistent dimensions");
-  endif
-  
-  if (nargin < 4 || isempty (fun))
-    fun = @sum;
-  endif
-
   if (nargin < 5 || isempty (fillval))
     fillval = 0;
   endif
@@ -90,6 +77,71 @@
     error ("accumarray: sparse matrices limited to 2 dimensions");
   endif
 
+  if (nargin < 4 || isempty (fun))
+    fun = @sum;
+    ## This is the fast summation case. Unlike the general case,
+    ## this case will be handled using an O(N) algorithm.
+
+    if (isspar && fillval == 0)
+      ## The "sparse" function can handle this case.
+
+      if ((nargin < 3 || isempty (sz)))
+        A = sparse (subs(:,1), subs(:,2), val);
+      elseif (length (sz) == 2)
+        A = sparse (subs(:,1), subs(:,2), val, sz(1), sz(2));
+      else
+        error ("accumarray: dimensions mismatch")
+      endif
+    else
+      ## This case is handled by an internal function.
+
+      if (ndims > 1)
+        if ((nargin < 3 || isempty (sz)))
+          sz = max (subs);
+        elseif (ndims != length (sz))
+          error ("accumarray: dimensions mismatch")
+        elseif (any (max (subs) > sz))
+          error ("accumarray: index out of range")
+        endif
+
+        ## Convert multidimensional subscripts.
+        subs = sub2ind (sz, mat2cell (subs, rows (subs), ones (1, ndims)){:});
+      elseif (nargin < 3)
+        ## In case of linear indexing, the fast built-in accumulator
+        ## will determine the extent for us.
+        sz = [];
+      endif
+
+      ## Call the built-in accumulator.
+      if (isempty (sz))
+        A = __accumarray_sum__ (subs, val);
+      else
+        A = __accumarray_sum__ (subs, val, prod (sz));
+        ## set proper shape.
+        A = reshape (A, sz);
+      endif
+
+      ## we fill in nonzero fill value.
+      if (fillval != 0)
+        mask = true (size (A));
+        mask(subs) = false;
+        A(mask) = fillval;
+      endif
+    endif
+
+    return
+  endif
+
+  if (nargin < 3 || isempty (sz))
+    sz = max (subs);
+    if (isscalar(sz))
+      sz = [sz, 1];
+    endif
+  elseif (length (sz) != ndims
+	  && (ndims != 1 || length (sz) != 2 || sz(2) != 1))
+    error ("accumarray: inconsistent dimensions");
+  endif
+  
   [subs, idx] = sortrows (subs);
 
   if (isscalar (val))