exprtk_gcd.cpp

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/*
 **************************************************************
 *         C++ Mathematical Expression Toolkit Library        *
 *                                                            *
 * ExprTk Greatest Common Divisor Example                     *
 * Author: Arash Partow (1999-2025)                           *
 * URL: https://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 MIT License.                   *
 * https://www.opensource.org/licenses/MIT                    *
 * SPDX-License-Identifier: MIT                               *
 *                                                            *
 **************************************************************
*/
 
 
#include <cstdio>
#include <string>
 
#include "exprtk.hpp"
 
 
template <typename T>
T gcd_println(T x, T y, T z)
{
   printf("gcd(%2d,%2d) = %2d\n",
          static_cast<int>(x),
          static_cast<int>(y),
          static_cast<int>(z));
 
   return T(0);
}
 
template <typename T>
void gcd()
{
   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;
   typedef typename compositor_t::function function_t;
 
   symbol_table_t symbol_table;
   symbol_table.add_function("println",gcd_println);
 
   compositor_t compositor(symbol_table);
 
   // define function: gcd(x,y)
   compositor.add(
      function_t("gcd")
      .vars("x","y")
      .expression
      (
         " switch                         "
         " {                              "
         "    case 0 = x : 0;             "
         "    case 0 = y : x;             "
         "    case x = y : x;             "
         "    case x > y : gcd(x - y, y); "
         "    default    : gcd(x, y - x); "
         " }                              "
      ));
 
   const std::string gcd_program =
      " i := 0;                        "
      " while ((i += 1) < 100)         "
      " {                              "
      "    j := 0;                     "
      "    repeat                      "
      "       println(i, j, gcd(i,j)); "
      "    until ((j += 1) >= 100);    "
      " };                             ";
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
   parser.enable_unknown_symbol_resolver();
   parser.compile(gcd_program,expression);
 
   expression.value();
}
 
int main()
{
   gcd<double>();
   return 0;
}