C++ Mathematical Expression Library (ExprTk) http://www.partow.net/programming/exprtk/index.html

exprtk_simple_example_10.cpp

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+/*
+ **************************************************************
+ *         C++ Mathematical Expression Toolkit Library        *
+ *                                                            *
+ * Simple Example 10                                          *
+ * Author: Arash Partow (1999-2013)                           *
+ * URL: http://www.partow.net/programming/exprtk/index.html   *
+ *                                                            *
+ * Copyright notice:                                          *
+ * Free use of the Mathematical Expression Toolkit Library is *
+ * permitted under the guidelines and in accordance with the  *
+ * most current version of the Common Public License.         *
+ * http://www.opensource.org/licenses/cpl1.0.php              *
+ *                                                            *
+ **************************************************************
+*/
+
+
+#include <cmath>
+#include <cstdio>
+#include <string>
+#include "exprtk.hpp"
+
+
+template <typename T>
+void newton_sqrt()
+{
+   typedef exprtk::symbol_table<T>      symbol_table_t;
+   typedef exprtk::expression<T>          expression_t;
+   typedef exprtk::parser<T>                  parser_t;
+   typedef exprtk::function_compositor<T> compositor_t;
+
+   T x = T(0);
+
+   exprtk::symbol_table<T> symbol_table;
+
+   symbol_table.add_constants();
+   symbol_table.add_variable("x",x);
+
+   compositor_t compositor(symbol_table);
+
+   compositor
+      .add("newton_sqrt_impl",
+           "switch                                "
+           "{                                     "
+           "  case x < 0  : -inf;                 "
+           "  case x == 0 : 0;                    "
+           "  case x == 1 : 1;                    "
+           "  default:                            "
+           "  ~{                                  "
+           "     z := 100;                        "
+           "     y := x / 2;                      "
+           "     while ((z := (z - 1)) > 0)       "
+           "     {                                "
+           "       if (equal(y * y,x), z := 0, 0);"
+           "       y := (1 / 2) * (y + (x / y))   "
+           "     }                                "
+           "   };                                 "
+           "}                                     ",
+           "x","y","z");
+
+   compositor
+      .add("newton_sqrt",
+           "newton_sqrt_impl(x,0,0)","x");
+
+   std::string expression_str = "newton_sqrt(x)";
+
+   expression_t expression;
+
+   expression.register_symbol_table(symbol_table);
+
+   exprtk::parser<T> parser;
+
+   parser.compile(expression_str,expression);
+
+   for (std::size_t i = 0; i < 100; ++i)
+   {
+      x = i;
+      T result = expression.value();
+      printf("sqrt(%03d) - Result: %12.10f\tReal: %12.10f\n",
+             static_cast<unsigned int>(i),
+             result,
+             std::sqrt(x));
+   }
+}
+
+int main()
+{
+   newton_sqrt<double>();
+   return 0;
+}