# ifndef CPPAD_LOCAL_OPTIMIZE_MATCH_OP_HPP
# define CPPAD_LOCAL_OPTIMIZE_MATCH_OP_HPP
// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-24 Bradley M. Bell
// ----------------------------------------------------------------------------
# include <cppad/local/optimize/hash_code.hpp>
// BEGIN_CPPAD_LOCAL_OPTIMIZE_NAMESPACE
namespace CppAD { namespace local { namespace optimize  {
/*
{xrst_begin optimize_match_op dev}
{xrst_spell
   erfc
}

Search for a Previous Operator that Matches Current Operator
############################################################

Syntax
******
| *exceed_collision_limit* = ``match_op`` (
| |tab| ``collision_limit`` ,
| |tab| ``random_itr`` ,
| |tab| ``op_previous`` ,
| |tab| ``current`` ,
| |tab| ``hash_tape_op`` ,
| |tab| ``work_bool`` ,
| |tab| ``work_addr_t``
| )

Prototype
*********
{xrst_literal
   // BEGIN_PROTOTYPE
   // END_PROTOTYPE
}

Operator Arguments
******************
If an argument for the current operator is a variable,
and the argument has previous match,
the previous match for the argument is used when checking for a match
for the current operator.

collision_limit
***************
is the maximum number of collisions (matches) allowed for one
expression hash code value.

random_itr
**********
is a random iterator for the old operation sequence.

op_previous
***********
Mapping from operator index to previous operator that can replace this one.
The input value of

   *previous* = *op_previous* [ *current* ]

is assumed to be zero.  If a match if found, the output value of
*previous* is set to the matching operator index,
otherwise it is left as is.  Note that *previous* < *current*
and *op_previous* [ ``previous`` ] is zero.

current
*******
is the index of the current operator which cannot be any of the
operators in the list below:
{xrst_literal
   // BEGIN_INVALID_OP
   // END_INVALID_OP
}
After this initialization, the value of *current*
increases with each call to match_op.

erf
===
The operators ``ErfOp`` and ``ErfcOp`` have
three arguments, but only one true argument (the others are always the same).

hash_table_op
*************
is assumed to be initialized as a vector of empty sets before the
first call to match_op (for a pass of the operation sequence).

| |tab| *hash_table_op* . ``n_set`` () == ``CPPAD_HASH_TABLE_SIZE``
| |tab| *hash_table_op* . ``end`` ()   == *op_previous* . ``size`` ()

If *i_op* is an element of the j-th set,
then the operation *op_previous* [ *i_op* ] has hash code j,
and does not match any other element of the j-th set.
An entry to j-th set for the current operator is added each time
match_op is called and a match for the current operator is not found.

work_bool
*********
work space that is used by match_op between calls to increase speed.
Should be empty on first call for this forward pass of the operation
sequence and not modified until forward pass is done

work_addr_t
***********
work space that is used by match_op between calls to increase speed.
Should be empty on first call for this forward pass of the operation
sequence and not modified until forward pass is done

exceed_collision_limit
**********************
If the *collision_limit* is exceeded (is not exceeded),
the return value is true (false).

{xrst_end optimize_match_op}
*/
// BEGIN_PROTOTYPE
template <class Addr>
bool match_op(
   size_t                                      collision_limit ,
   const play::const_random_iterator<Addr>&    random_itr      ,
   pod_vector<addr_t>&                         op_previous     ,
   size_t                                      current         ,
   sparse::list_setvec&                        hash_table_op   ,
   pod_vector<bool>&                           work_bool       ,
   pod_vector<addr_t>&                         work_addr_t     )
// END_PROTOTYPE
{
# ifndef NDEBUG
   switch( random_itr.get_op(current) )
   {
      // BEGIN_INVALID_OP
      case BeginOp:
      case CExpOp:
      case CSkipOp:
      case CSumOp:
      case EndOp:
      case InvOp:
      case LdpOp:
      case LdvOp:
      case ParOp:
      case PriOp:
      case StppOp:
      case StpvOp:
      case StvpOp:
      case StvvOp:
      case AFunOp:
      case FunapOp:
      case FunavOp:
      case FunrpOp:
      case FunrvOp:
      // END_INVALID_OP
      CPPAD_ASSERT_UNKNOWN(false);
      break;

      default:
      break;
   }
# endif
   // initialize return value
   bool exceed_collision_limit = false;
   // num_op
   size_t num_op = random_itr.num_op();
   //
   // num_var
   size_t num_var = random_itr.num_var();
   //
   // variable is a reference to, and better name for, work_bool
   pod_vector<bool>&  variable(work_bool);
   //
   // var2previous_var is a reference to, and better name for, work_addr_t
   pod_vector<addr_t>&  var2previous_var(work_addr_t);
   if( var2previous_var.size() == 0 )
   {  var2previous_var.resize(num_var);
      for(size_t i = 0; i < num_var; ++i)
         var2previous_var[i] = addr_t(i);
   }
   //
   CPPAD_ASSERT_UNKNOWN( var2previous_var.size() == num_var );
   CPPAD_ASSERT_UNKNOWN( num_op == op_previous.size() );
   CPPAD_ASSERT_UNKNOWN( op_previous[current] == 0 );
   CPPAD_ASSERT_UNKNOWN(
      hash_table_op.n_set() == CPPAD_HASH_TABLE_SIZE
   );
   CPPAD_ASSERT_UNKNOWN( hash_table_op.end() == num_op );
   CPPAD_ASSERT_UNKNOWN( current < num_op );
   //
   // op, arg, i_var
   op_code_var   op;
   const addr_t* arg;
   size_t        i_var;
   random_itr.op_info(current, op, arg, i_var);
   //
   // num_arg
   size_t num_arg = NumArg(op);
   CPPAD_ASSERT_UNKNOWN( 0 < num_arg );
   CPPAD_ASSERT_UNKNOWN(
      (num_arg < 3) || ( (num_arg == 3) && (op == ErfOp || op == ErfcOp) )
   );
   //
   arg_is_variable(op, arg, variable);
   CPPAD_ASSERT_UNKNOWN( variable.size() == num_arg );
   //
   // If j-th argument to this operator is a variable, and a previous
   // variable will be used in its place, use the previous variable for
   // hash coding and matching.
   addr_t arg_match[] = {
      // Invalid value that will not be used. This initialization avoid
      // a warning on some compilers
      std::numeric_limits<addr_t>::max(),
      std::numeric_limits<addr_t>::max(),
      std::numeric_limits<addr_t>::max()
   };
   if( (op == AddvvOp) || (op == MulvvOp ) )
   {  // in special case where operator is commutative and operands are variables,
      // put lower index first so hash code does not depend on operator order
      CPPAD_ASSERT_UNKNOWN( num_arg == 2 );
      arg_match[0] = var2previous_var[ arg[0] ];
      arg_match[1] = var2previous_var[ arg[1] ];
      if( arg_match[1] < arg_match[0] )
         std::swap( arg_match[0], arg_match[1] );
   }
   else for(size_t j = 0; j < num_arg; ++j)
   {  arg_match[j] = arg[j];
      if( variable[j] )
         arg_match[j] = var2previous_var[ arg[j] ];
   }

   //
   size_t code = optimize_hash_code(opcode_t(op), num_arg, arg_match);
   //
   // iterator for the set with this hash code
   sparse::list_setvec_const_iterator itr(hash_table_op, code);
   //
   // check for a match
   size_t count = 0;
   while( *itr != num_op )
   {  ++count;
      //
      // candidate previous for current operator
      size_t  candidate  = *itr;
      CPPAD_ASSERT_UNKNOWN( candidate < current );
      CPPAD_ASSERT_UNKNOWN( op_previous[candidate] == 0 );
      //
      op_code_var   op_c;
      const addr_t* arg_c;
      size_t        i_var_c;
      random_itr.op_info(candidate, op_c, arg_c, i_var_c);
      //
      // check for a match
      bool match = op == op_c;
      size_t j   = 0;
      while( match & (j < num_arg) )
      {  if( variable[j] )
            match &= arg_match[j] == var2previous_var[ arg_c[j] ];
         else
            match &= arg_match[j] == arg_c[j];
         ++j;
      }
      if( (! match) && ( (op == AddvvOp) || (op == MulvvOp) ) )
      {  // communative so check for reverse order match
         match  = op == op_c;
         //
         // 2024-02-14:
         // If op_c is not AddvvOp or MulvvOp, its arguments may not be
         // variables and the code below could attempt to access
         // var2previous_var out of range. See 2024@mm-dd@02-14.
         if( match )
         {  match &= arg_match[0] == var2previous_var[ arg_c[1] ];
            match &= arg_match[1] == var2previous_var[ arg_c[0] ];
         }
      }
      if( match )
      {  op_previous[current] = static_cast<addr_t>( candidate );
         if( NumRes(op) > 0 )
         {  CPPAD_ASSERT_UNKNOWN( i_var_c < i_var );
            var2previous_var[i_var] = addr_t( i_var_c );
         }
         return exceed_collision_limit;
      }
      ++itr;
   }

   // see print (that is commented out) at bottom of get_op_previous.hpp
   CPPAD_ASSERT_UNKNOWN( count <= collision_limit );
   if( count == collision_limit )
   {  // restart the list
      hash_table_op.clear(code);
      // limit has been exceeded
      exceed_collision_limit = true;
   }
   // No match was found. Add this operator to the set for this hash code
   // Not using post_element because we need to iterate for
   // this code before adding another element for this code.
   hash_table_op.add_element(code, current);
   //
   return exceed_collision_limit;
}

} } } // END_CPPAD_LOCAL_OPTIMIZE_NAMESPACE

# endif
