[patch] External data access example

[Don McCoy <don@xxxxxxxxxxxxxxxx>]

This patch adds an example where the values of a VSIPL++ Matrix are 
altered using a direct pointer to the underlying data.  This is useful 
for performing operations on data outside the VSIPL++ library.
Regards,

--
Don McCoy
don (at) CodeSourcery
(888) 776-0262 / (650) 331-3385, x712

2007-06-26  Don McCoy  <don@xxxxxxxxxxxxxxxx>

	* examples/extdata.cpp: New file.  Example demonstrating the
	  use of the Ext_data interface to access a view's underlying
	  data via a pointer.

Index: examples/extdata.cpp
===================================================================
--- examples/extdata.cpp	(revision 0)
+++ examples/extdata.cpp	(revision 0)
@@ -0,0 +1,48 @@
+/* Copyright (c) 2007 by CodeSourcery.  All rights reserved.
+*/
+/** @file    examples/extdata.cpp
+    @author  Don McCoy
+    @date    2007-07-23
+    @brief   VSIPL++ Library: Simple example for external data access.
+*/
+
+#include <iostream>
+#include <vsip/initfin.hpp>
+#include <vsip/matrix.hpp>
+#include <vsip/opt/extdata.hpp>
+
+
+int 
+main(int argc, char **argv)
+{
+  vsip::vsipl init(argc, argv);
+
+  const vsip::length_type M = 128;
+  const vsip::length_type N = 64;
+  
+  typedef vsip::scalar_f T;
+  typedef vsip::Dense<2, T, vsip::row2_type> block_type;
+  typedef vsip::Matrix<T, block_type> view_type;
+
+  view_type grid(M, N, 1.234f);
+
+  std::cout << "first and last values (before): " << grid.get(0,0) 
+            << ", " << grid.get(M-1,N-1) << std::endl;
+
+  // Control the scope of the Ext_data object.  Synchronization is forced
+  // when the object is destroyed in accordance with the SYNC_OUT parameter.
+  {
+    vsip::impl::Ext_data<block_type> ext(grid.block(), vsip::impl::SYNC_OUT);
+
+    T* ptr = ext.data();
+    for (vsip::length_type i = 0; i < M; ++i)
+      for (vsip::length_type j = 0; j < N; ++j)
+        *(ptr + i*N + j) = i*N + j;
+    std::cout << "ptr = " << ptr << std::endl;
+  }
+   
+  std::cout << "first and last values (after):  " << grid.get(0,0) 
+            << ", " << grid.get(M-1,N-1) << std::endl;
+
+  return 0;
+}