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direct/src/dcparser/hashGenerator.cxx

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// Filename: hashGenerator.cxx
// Created by:  drose (22Mar01)
//
////////////////////////////////////////////////////////////////////
//
// PANDA 3D SOFTWARE
// Copyright (c) 2001, Disney Enterprises, Inc.  All rights reserved
//
// All use of this software is subject to the terms of the Panda 3d
// Software license.  You should have received a copy of this license
// along with this source code; you will also find a current copy of
// the license at http://www.panda3d.org/license.txt .
//
// To contact the maintainers of this program write to
// panda3d@yahoogroups.com .
//
////////////////////////////////////////////////////////////////////

#include "hashGenerator.h"
#include "primeNumberGenerator.h"

// We multiply each consecutive integer by the next prime number and
// add it to the total.  This will generate pretty evenly-distributed
// hash numbers for an arbitrary sequence of ints.

// We do recycle the prime number table at some point, just to keep it
// from growing insanely large, however (and to avoid wasting time
// computing large prime numbers unnecessarily), and we also truncate
// the result to the low-order 32 bits.

static const int max_prime_numbers = 10000;

////////////////////////////////////////////////////////////////////
//     Function: HashGenerator::Constructor
//       Access: Public
//  Description:
////////////////////////////////////////////////////////////////////
HashGenerator::
HashGenerator() {
  _hash = 0;
  _index = 0;
}

////////////////////////////////////////////////////////////////////
//     Function: HashGenerator::add_int
//       Access: Public
//  Description: Adds another integer to the hash so far.
////////////////////////////////////////////////////////////////////
void HashGenerator::
add_int(int num) {
  nassertv(_index >= 0 && _index < max_prime_numbers);
  _hash += _primes[_index] * num;
  _index = (_index + 1) % max_prime_numbers;
}

////////////////////////////////////////////////////////////////////
//     Function: HashGenerator::add_string
//       Access: Public
//  Description: Adds a string to the hash, by breaking it down into a
//               sequence of integers.
////////////////////////////////////////////////////////////////////
void HashGenerator::
add_string(const string &str) {
  add_int(str.length());
  string::const_iterator si;
  for (si = str.begin(); si != str.end(); ++si) {
    add_int(*si);
  }
}

////////////////////////////////////////////////////////////////////
//     Function: HashGenerator::get_hash
//       Access: Public
//  Description: Returns the hash number generated.
////////////////////////////////////////////////////////////////////
unsigned long HashGenerator::
get_hash() const {
  return (unsigned long)(_hash & 0xffffffff);
}

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