init

Step8/MathFunctions/CMakeLists.txt

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+add_library(MathFunctions mysqrt.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}
+          )
+
+# link our compiler flags interface library
+target_link_libraries(MathFunctions tutorial_compiler_flags)
+
+# does this system provide the log and exp functions?
+include(CheckCXXSourceCompiles)
+check_cxx_source_compiles("
+  #include <cmath>
+  int main() {
+    std::log(1.0);
+    return 0;
+  }
+" HAVE_LOG)
+check_cxx_source_compiles("
+  #include <cmath>
+  int main() {
+    std::exp(1.0);
+    return 0;
+  }
+" HAVE_EXP)
+
+# add compile definitions
+if(HAVE_LOG AND HAVE_EXP)
+  target_compile_definitions(MathFunctions
+                             PRIVATE "HAVE_LOG" "HAVE_EXP")
+endif()
+
+# install libs
+set(installable_libs MathFunctions tutorial_compiler_flags)
+install(TARGETS ${installable_libs} DESTINATION lib)
+# install include headers
+install(FILES MathFunctions.h DESTINATION include)

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
+}

Step8/MathFunctions/MathFunctions.h

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+double mysqrt(double x);

Step8/MathFunctions/mysqrt.cxx

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+#include <cmath>
+#include <iostream>
+
+#include "MathFunctions.h"
+
+// 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 = std::exp(std::log(x) * 0.5);
+  std::cout << "Computing sqrt of " << x << " to be " << result
+            << " using log and exp" << std::endl;
+#else
+  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;
+  }
+#endif
+  return result;
+}