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+Step 6: Adding a Custom Command and Generated File
+==================================================
+
+Suppose, for the purpose of this tutorial, we decide that we never want to use
+the platform ``log`` and ``exp`` functions and instead would like to
+generate a table of precomputed values to use in the ``mysqrt`` function.
+In this section, we will create the table as part of the build process,
+and then compile that table into our application.
+
+First, let's remove the check for the ``log`` and ``exp`` functions in
+``MathFunctions/CMakeLists.txt``. Then remove the check for ``HAVE_LOG`` and
+``HAVE_EXP`` from ``mysqrt.cxx``. At the same time, we can remove
+:code:`#include <cmath>`.
+
+In the ``MathFunctions`` subdirectory, a new source file named
+``MakeTable.cxx`` has been provided to generate the table.
+
+After reviewing the file, we can see that the table is produced as valid C++
+code and that the output filename is passed in as an argument.
+
+The next step is to add the appropriate commands to the
+``MathFunctions/CMakeLists.txt`` file to build the MakeTable executable and
+then run it as part of the build process. A few commands are needed to
+accomplish this.
+
+First, at the top of ``MathFunctions/CMakeLists.txt``, the executable for
+``MakeTable`` is added as any other executable would be added.
+
+.. literalinclude:: Step7/MathFunctions/CMakeLists.txt
+  :caption: MathFunctions/CMakeLists.txt
+  :name: MathFunctions/CMakeLists.txt-add_executable-MakeTable
+  :language: cmake
+  :start-after: # first we add the executable that generates the table
+  :end-before: # add the command to generate the source code
+
+Then we add a custom command that specifies how to produce ``Table.h``
+by running MakeTable.
+
+.. literalinclude:: Step7/MathFunctions/CMakeLists.txt
+  :caption: MathFunctions/CMakeLists.txt
+  :name: MathFunctions/CMakeLists.txt-add_custom_command-Table.h
+  :language: cmake
+  :start-after: # add the command to generate the source code
+  :end-before: # add the main library
+
+Next we have to let CMake know that ``mysqrt.cxx`` depends on the generated
+file ``Table.h``. This is done by adding the generated ``Table.h`` to the list
+of sources for the library MathFunctions.
+
+.. literalinclude:: Step7/MathFunctions/CMakeLists.txt
+  :caption: MathFunctions/CMakeLists.txt
+  :name: MathFunctions/CMakeLists.txt-add_library-Table.h
+  :language: cmake
+  :start-after: # add the main library
+  :end-before: # state that anybody linking
+
+We also have to add the current binary directory to the list of include
+directories so that ``Table.h`` can be found and included by ``mysqrt.cxx``.
+
+.. literalinclude:: Step7/MathFunctions/CMakeLists.txt
+  :caption: MathFunctions/CMakeLists.txt
+  :name: MathFunctions/CMakeLists.txt-target_include_directories-Table.h
+  :language: cmake
+  :start-after: # state that we depend on our bin
+  :end-before: # install rules
+
+Now let's use the generated table. First, modify ``mysqrt.cxx`` to include
+``Table.h``. Next, we can rewrite the ``mysqrt`` function to use the table:
+
+.. literalinclude:: Step7/MathFunctions/mysqrt.cxx
+  :caption: MathFunctions/mysqrt.cxx
+  :name: MathFunctions/mysqrt.cxx
+  :language: c++
+  :start-after: // a hack square root calculation using simple operations
+
+Run the :manual:`cmake  <cmake(1)>` executable or the
+:manual:`cmake-gui <cmake-gui(1)>` to configure the project and then build it
+with your chosen build tool.
+
+When this project is built it will first build the ``MakeTable`` executable.
+It will then run ``MakeTable`` to produce ``Table.h``. Finally, it will
+compile ``mysqrt.cxx`` which includes ``Table.h`` to produce the
+``MathFunctions`` library.
+
+Run the Tutorial executable and verify that it is using the table.