# ifndef CPPAD_LOCAL_HASH_CODE_HPP
# define CPPAD_LOCAL_HASH_CODE_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/core/base_hash.hpp>
/*!
\file local/hash_code.hpp
CppAD hashing utility.
*/


namespace CppAD { namespace local { // BEGIN_CPPAD_LOCAL_NAMESPACE
/*!
General purpose hash code for an arbitrary value.

\tparam Value
is the type of the argument being hash coded.
It should be a plain old data class; i.e.,
the values included in the equality operator in the object and
not pointed to by the object.

\param value
the value that we are generating a hash code for.
All of the fields in value should have been set before the hash code
is computed (otherwise undefined values are used).

\return
is a hash code that is between zero and CPPAD_HASH_TABLE_SIZE - 1.

\par Checked Assertions
\li std::numeric_limits<unsigned short>::max() >= CPPAD_HASH_TABLE_SIZE
\li sizeof(value) is even
\li sizeof(unsigned short)  == 2
*/
template <class Value>
unsigned short local_hash_code(const Value& value)
{  CPPAD_ASSERT_UNKNOWN(
      std::numeric_limits<unsigned short>::max()
      >=
      CPPAD_HASH_TABLE_SIZE
   );
   CPPAD_ASSERT_UNKNOWN( sizeof(unsigned short) == 2 );
   CPPAD_ASSERT_UNKNOWN( sizeof(value) % 2  == 0 );
   //
   const unsigned short* v
             = reinterpret_cast<const unsigned short*>(& value);
   //
   size_t i = sizeof(value) / 2 - 1;
   //
   size_t sum = v[i];
   //
   while(i--)
      sum += v[i];
   //
   unsigned short code = static_cast<unsigned short>(
      sum % CPPAD_HASH_TABLE_SIZE
   );
   return code;
}

/*!
Specialized hash code for a CppAD operator and its arguments.

\param op
is the operator that we are computing a hash code for.
If it is not one of the following operartors, the operator is not
hash coded and zero is returned:

\li unary operators:
AbsOp, AcosOp, AcoshOp, AsinOp, AsinhOp, AtanOp, AtanhOp, CosOp, CoshOp
ExpOp, Expm1Op, LogOp, Log1pOp, SinOp, SinhOp, SqrtOp, TanOp, TanhOp

\li binary operators where first argument is a parameter:
AddpvOp, DivpvOp, MulpvOp, PowpvOp, SubpvOp, ZmulpvOp

\li binary operators where second argument is a parameter:
DivvpOp, PowvpOp, SubvpOp, Zmulvp

\li binary operators where first is an index and second is a variable:
DisOp

\li binary operators where both arguments are variables:
AddvvOp, DivvvOp, MulvvOp, PowvvOp, SubvvOp, ZmulvvOp

\param arg
is a vector of length NumArg(op) or 2 (which ever is smaller),
containing the corresponding argument indices for this operator.

\param npar
is the number of parameters corresponding to this operation sequence.

\param par
is a vector of length npar containing the parameters
for this operation sequence; i.e.,
given a parameter index of i, the corresponding parameter value is
 par[i].


\return
is a hash code that is between zero and CPPAD_HASH_TABLE_SIZE - 1.

\par Checked Assertions
 op must be one of the operators specified above. In addition,
\li std::numeric_limits<unsigned short>::max() >= CPPAD_HASH_TABLE_SIZE
\li sizeof(size_t) is even
\li sizeof(Base) is even
\li sizeof(unsigned short)  == 2
\li size_t(op) < size_t(NumberOp) <= CPPAD_HASH_TABLE_SIZE
\li if the j-th argument for this operation is a parameter, arg[j] < npar.
*/

template <class Base>
unsigned short local_hash_code(
   op_code_var   op      ,
   const addr_t* arg     ,
   size_t        npar    ,
   const Base*   par     )
{  CPPAD_ASSERT_UNKNOWN(
      std::numeric_limits<unsigned short>::max()
      >=
      CPPAD_HASH_TABLE_SIZE
   );
   CPPAD_ASSERT_UNKNOWN( size_t (op) < size_t(NumberOp) );
   CPPAD_ASSERT_UNKNOWN( sizeof(unsigned short) == 2 );
   CPPAD_ASSERT_UNKNOWN( sizeof(addr_t) % 2  == 0 );
   CPPAD_ASSERT_UNKNOWN( sizeof(Base) % 2  == 0 );
   unsigned short op_fac = static_cast<unsigned short> (
      CPPAD_HASH_TABLE_SIZE / static_cast<unsigned short>(NumberOp)
   );
   CPPAD_ASSERT_UNKNOWN( op_fac > 0 );

   // number of shorts per addr_t value
   size_t short_addr_t   = sizeof(addr_t) / 2;

   // initialize with value that separates operators as much as possible
   unsigned short code = static_cast<unsigned short>(
      static_cast<unsigned short>(op) * op_fac
   );

   // now code in the operands
   size_t i;
   const unsigned short* v;

   // first argument
   switch(op)
   {  // Binary operators where first arugment is a parameter.
      // Code parameters by value instead of
      // by index for two reasons. One, it gives better separation.
      // Two, different indices can be same parameter value.
      case AddpvOp:
      case DivpvOp:
      case MulpvOp:
      case PowpvOp:
      case SubpvOp:
      case ZmulpvOp:
      CPPAD_ASSERT_UNKNOWN( NumArg(op) == 2 );
      code += hash_code( par[arg[0]] );
      //
      v = reinterpret_cast<const unsigned short*>(arg + 1);
      i = short_addr_t;
      while(i--)
         code += v[i];
      break;

      // Binary operator where first argument is an index and
      // second is a variable (same as both variables).
      case DisOp:

      // Binary operators where both arguments are variables
      case AddvvOp:
      case DivvvOp:
      case MulvvOp:
      case PowvvOp:
      case SubvvOp:
      case ZmulvvOp:
      CPPAD_ASSERT_UNKNOWN( NumArg(op) == 2 );
      v = reinterpret_cast<const unsigned short*>(arg + 0);
      i = 2 * short_addr_t;
      while(i--)
         code += v[i];
      break;

      // Binary operators where second arugment is a parameter.
      case DivvpOp:
      case PowvpOp:
      case SubvpOp:
      case ZmulvpOp:
      CPPAD_ASSERT_UNKNOWN( NumArg(op) == 2 );
      v = reinterpret_cast<const unsigned short*>(arg + 0);
      i = short_addr_t;
      while(i--)
         code += v[i];
      code += hash_code( par[arg[1]] );
      break;

      // Unary operators
      case AbsOp:
      case AcosOp:
      case AcoshOp:
      case AsinOp:
      case AsinhOp:
      case AtanOp:
      case AtanhOp:
      case CosOp:
      case CoshOp:
      case ErfOp:
      case ErfcOp:
      case ExpOp:
      case Expm1Op:
      case LogOp:
      case Log1pOp:
      case SignOp:
      case SinOp:
      case SinhOp:
      case SqrtOp:
      case TanOp:
      case TanhOp:
      CPPAD_ASSERT_UNKNOWN( NumArg(op) == 1 || op == ErfOp );
      v = reinterpret_cast<const unsigned short*>(arg + 0);
      i = short_addr_t;
      while(i--)
         code += v[i];
      break;

      // should have been one of he cases above
      default:
      CPPAD_ASSERT_UNKNOWN(false);
   }

   return code % CPPAD_HASH_TABLE_SIZE;
}

} } // END_CPPAD_LOCAL_NAMESPACE

# endif
