Started a cmake tutorial

Step9/MathFunctions/CMakeLists.txt

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+add_library(MathFunctions MathFunctions.cxx)
+
+# state that anybody linking to us needs to include the current source dir
+# to find MathFunctions.h, while we don't.
+target_include_directories(MathFunctions
+                           INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
+                           )
+
+# should we use our own math functions
+option(USE_MYMATH "Use tutorial provided math implementation" ON)
+if (USE_MYMATH)
+  target_compile_definitions(MathFunctions PRIVATE "USE_MYMATH")
+
+  # generate Table.h
+  include(MakeTable.cmake)
+
+  # library that just does sqrt
+  add_library(SqrtLibrary STATIC
+              mysqrt.cxx
+              ${CMAKE_CURRENT_BINARY_DIR}/Table.h
+              )
+
+  # state that we depend on our binary dir to find Table.h
+  target_include_directories(SqrtLibrary PRIVATE
+                             ${CMAKE_CURRENT_BINARY_DIR}
+                             )
+
+  # link SqrtLibrary to tutorial_compiler_flags
+  target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
+
+  target_link_libraries(MathFunctions PRIVATE SqrtLibrary)
+endif()
+
+# link MathFunctions to tutorial_compiler_flags
+target_link_libraries(MathFunctions PUBLIC tutorial_compiler_flags)
+
+# install libs
+set(installable_libs MathFunctions tutorial_compiler_flags)
+if(TARGET SqrtLibrary)
+  list(APPEND installable_libs SqrtLibrary)
+endif()
+install(TARGETS ${installable_libs} DESTINATION lib)
+# install include headers
+install(FILES MathFunctions.h DESTINATION include)

Step9/MathFunctions/MakeTable.cmake

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+# first we add the executable that generates the table
+add_executable(MakeTable MakeTable.cxx)
+target_link_libraries(MakeTable PRIVATE tutorial_compiler_flags)
+
+# 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
+  )

Step9/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
+}

Step9/MathFunctions/MathFunctions.cxx

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+#include "MathFunctions.h"
+
+#include <cmath>
+
+#ifdef USE_MYMATH
+#  include "mysqrt.h"
+#endif
+
+namespace mathfunctions {
+double sqrt(double x)
+{
+// which square root function should we use?
+#ifdef USE_MYMATH
+  return detail::mysqrt(x);
+#else
+  return std::sqrt(x);
+#endif
+}
+}

Step9/MathFunctions/MathFunctions.h

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+#pragma once
+
+namespace mathfunctions {
+double sqrt(double x);
+}

Step9/MathFunctions/mysqrt.cxx

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+#include "mysqrt.h"
+
+#include <iostream>
+
+// include the generated table
+#include "Table.h"
+
+namespace mathfunctions {
+namespace detail {
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  // use the table to help find an initial value
+  double result = x;
+  if (x >= 1 && x < 10) {
+    std::cout << "Use the table to help find an initial value " << std::endl;
+    result = sqrtTable[static_cast<int>(x)];
+  }
+
+  // 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;
+  }
+
+  return result;
+}
+}
+}

Step9/MathFunctions/mysqrt.h

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+#pragma once
+
+namespace mathfunctions {
+namespace detail {
+double mysqrt(double x);
+}
+}