Started a cmake tutorial

Step7/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")
+
+  # library that just does sqrt
+  add_library(SqrtLibrary STATIC
+              mysqrt.cxx
+              )
+
+  # link SqrtLibrary to tutorial_compiler_flags
+  target_link_libraries(SqrtLibrary PUBLIC tutorial_compiler_flags)
+
+  # TODO 1: Include CheckCXXSourceCompiles
+
+  # TODO 2: Use check_cxx_source_compiles with simple C++ code to verify
+  # availability of:
+  # * std::log
+  # * std::exp
+  # Store the results in HAVE_LOG and HAVE_EXP respectively.
+
+  # Hint: Sample C++ code which uses log:
+  # #include <cmath>
+  # int main() {
+  #   std::log(1.0);
+  #   return 0;
+  # }
+
+  # TODO 3: Conditionally on HAVE_LOG and HAVE_EXP, add private compile
+  # definitions "HAVE_LOG" and "HAVE_EXP" to the SqrtLibrary target.
+
+  # Hint: Use target_compile_definitions()
+
+  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)

Step7/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
+}
+}

Step7/MathFunctions/MathFunctions.h

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

Step7/MathFunctions/mysqrt.cxx

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+#include "mysqrt.h"
+
+#include <iostream>
+
+namespace mathfunctions {
+namespace detail {
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  // TODO 5: If both HAVE_LOG and HAVE_EXP are defined,  use the following:
+  //// double result = std::exp(std::log(x) * 0.5);
+  //// std::cout << "Computing sqrt of " << x << " to be " << result
+  ////        << " using log and exp" << std::endl;
+  // else, use the existing logic.
+
+  // Hint: Don't forget the #endif before returning the result!
+
+  double result = 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;
+}
+}
+}

Step7/MathFunctions/mysqrt.h

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