// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-22 Bradley M. Bell
// ----------------------------------------------------------------------------
/*
{xrst_begin optimize_conditional_skip.cpp}

Optimize Conditional Expressions: Example and Test
##################################################

See Also
********
:ref:`cond_exp.cpp-name`

{xrst_literal
   // BEGIN C++
   // END C++
}

{xrst_end optimize_conditional_skip.cpp}
*/
// BEGIN C++
# include <cppad/cppad.hpp>
namespace {
   struct tape_size { size_t n_var; size_t n_op; };

   template <class Vector> void fun(
      const std::string& options ,
      const Vector& x, Vector& y, tape_size& before, tape_size& after
   )
   {  typedef typename Vector::value_type scalar;


      // phantom variable with index 0 and independent variables
      // begin operator, independent variable operators and end operator
      before.n_var = 1 + x.size(); before.n_op  = 2 + x.size();
      after.n_var  = 1 + x.size(); after.n_op   = 2 + x.size();

      // Create a variable that is is only used as left operand
      // in the comparison operation
      scalar left = 1. / x[0];
      before.n_var += 1; before.n_op += 1;
      after.n_var  += 1; after.n_op  += 1;

      // right operand in comparison operation
      scalar right  = x[0];
      before.n_var += 0; before.n_op  += 0;
      after.n_var  += 0; after.n_op   += 0;

      // Note that the left and right operand in the CondExpLt comparison
      // are determined at this point. Hence the conditional skip operator
      // will be inserted here so that the operations mentioned below can
      // also be skipped during zero order forward mode.
      if( options.find("no_conditional_skip") == std::string::npos )
         after.n_op += 1; // for conditional skip operation

      // Create a variable that is only used when comparison result is true
      // (can be skipped when the comparison result is false)
      scalar if_true = x[0] * 5.0;
      before.n_var += 1; before.n_op += 1;
      after.n_var  += 1; after.n_op  += 1;

      // Create two variables only used when the comparison result is false
      // (can be skipped when the comparison result is true)
      scalar temp      = 5.0 + x[0];
      scalar if_false  = temp * 3.0;
      before.n_var += 2; before.n_op += 2;
      after.n_var  += 2; after.n_op  += 2;

      // conditional comparison is 1 / x[0] < x[0]
      scalar value = CppAD::CondExpLt(left, right, if_true, if_false);
      before.n_var += 1; before.n_op += 1;
      after.n_var  += 1; after.n_op  += 1;

      // results for this operation sequence
      y[0] = value;
      before.n_var += 0; before.n_op  += 0;
      after.n_var  += 0; after.n_op   += 0;
   }
}

bool conditional_skip(void)
{  bool ok = true;
   using CppAD::AD;
   using CppAD::NearEqual;
   double eps10 = 10.0 * std::numeric_limits<double>::epsilon();

   // domain space vector
   size_t n  = 1;
   CPPAD_TESTVECTOR(AD<double>) ax(n);
   ax[0] = 0.5;

   // range space vector
   size_t m = 1;
   CPPAD_TESTVECTOR(AD<double>) ay(m);

   for(size_t k = 0; k < 2; k++)
   {  // optimization options
      std::string options = "";
      if( k == 0 )
         options = "no_conditional_skip";

      // declare independent variables and start tape recording
      CppAD::Independent(ax);

      // compute function computation
      tape_size before, after;
      fun(options, ax, ay, before, after);

      // create f: x -> y and stop tape recording
      CppAD::ADFun<double> f(ax, ay);
      ok &= f.size_order() == 1; // this constructor does 0 order forward
      ok &= f.size_var() == before.n_var;
      ok &= f.size_op()  == before.n_op;

      // Optimize the operation sequence
      f.optimize(options);
      ok &= f.size_order() == 0; // 0 order forward not present
      ok &= f.size_var() == after.n_var;
      ok &= f.size_op()  == after.n_op;

      // Check case where result of the comparison is true (x[0] > 1.0).
      CPPAD_TESTVECTOR(double) x(n), y(m), check(m);
      x[0] = 1.75;
      y    = f.Forward(0, x);
      fun(options, x, check, before, after);
      ok &= NearEqual(y[0], check[0], eps10, eps10);
      if( options == "" )
         ok  &= f.number_skip() == 2;
      else
         ok &= f.number_skip() == 0;

      // Check case where result of the comparison is false (x[0] <= 1.0)
      x[0] = 0.5;
      y    = f.Forward(0, x);
      fun(options, x, check, before, after);
      ok &= NearEqual(y[0], check[0], eps10, eps10);
      if( options == "" )
         ok  &= f.number_skip() == 1;
      else
         ok &= f.number_skip() == 0;
   }
   return ok;
}

// END C++
