Help/guide/tutorial: Adopt tutorial code

Help/guide/tutorial/Step8/MathFunctions/CMakeLists.txt

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+# first we add the executable that generates the table
+add_executable(MakeTable MakeTable.cxx)
+
+# add the command to generate the source code
+add_custom_command(
+  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/Table.h
+  COMMAND MakeTable ${CMAKE_CURRENT_BINARY_DIR}/Table.h
+  DEPENDS MakeTable
+  )
+
+# add the main library
+add_library(MathFunctions
+            mysqrt.cxx
+            ${CMAKE_CURRENT_BINARY_DIR}/Table.h
+            )
+
+# state that anybody linking to us needs to include the current source dir
+# to find MathFunctions.h, while we don't.
+# state that we depend on Tutorial_BINARY_DIR but consumers don't, as the
+# TutorialConfig.h include is an implementation detail
+# state that we depend on our binary dir to find Table.h
+target_include_directories(MathFunctions
+          INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
+          PRIVATE ${Tutorial_BINARY_DIR}
+                  ${CMAKE_CURRENT_BINARY_DIR}
+          )
+
+install(TARGETS MathFunctions DESTINATION lib)
+install(FILES MathFunctions.h DESTINATION include)

Help/guide/tutorial/Step8/MathFunctions/MakeTable.cxx

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+// A simple program that builds a sqrt table
+#include <cmath>
+#include <fstream>
+#include <iostream>
+
+int main(int argc, char* argv[])
+{
+  // make sure we have enough arguments
+  if (argc < 2) {
+    return 1;
+  }
+
+  std::ofstream fout(argv[1], std::ios_base::out);
+  const bool fileOpen = fout.is_open();
+  if (fileOpen) {
+    fout << "double sqrtTable[] = {" << std::endl;
+    for (int i = 0; i < 10; ++i) {
+      fout << sqrt(static_cast<double>(i)) << "," << std::endl;
+    }
+    // close the table with a zero
+    fout << "0};" << std::endl;
+    fout.close();
+  }
+  return fileOpen ? 0 : 1; // return 0 if wrote the file
+}

Help/guide/tutorial/Step8/MathFunctions/MathFunctions.h

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+double mysqrt(double x);

Help/guide/tutorial/Step8/MathFunctions/mysqrt.cxx

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+#include "MathFunctions.h"
+#include "TutorialConfig.h"
+#include <iostream>
+
+// include the generated table
+#include "Table.h"
+
+#include <cmath>
+
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  // if we have both log and exp then use them
+#if defined(HAVE_LOG) && defined(HAVE_EXP)
+  double result = exp(log(x) * 0.5);
+  std::cout << "Computing sqrt of " << x << " to be " << result << " using log"
+            << std::endl;
+#else
+  // use the table to help find an initial value
+  double result = x;
+  if (x >= 1 && x < 10) {
+    result = sqrtTable[static_cast<int>(x)];
+  }
+
+  // if we have both log and exp then use them
+
+  // do ten iterations
+  for (int i = 0; i < 10; ++i) {
+    if (result <= 0) {
+      result = 0.1;
+    }
+    double delta = x - (result * result);
+    result = result + 0.5 * delta / result;
+    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
+  }
+#endif
+  return result;
+}