Teuchos_HashUtils.cpp

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// @HEADER
// *****************************************************************************
//                    Teuchos: Common Tools Package
//
// Copyright 2004 NTESS and the Teuchos contributors.
// SPDX-License-Identifier: BSD-3-Clause
// *****************************************************************************
// @HEADER

#include "Teuchos_HashUtils.hpp"
#include "Teuchos_Assert.hpp"
#include "Teuchos_CompilerCodeTweakMacros.hpp"

using namespace Teuchos;


const int HashUtils::primeCount_ = 33;
const int HashUtils::primes_[]
= {11, 19, 37, 59, 101, 163, 271, 443, 733, 1187, 1907, 3061,
   4919, 7759, 12379, 19543, 30841, 48487, 75989,
   119089, 185971, 290347, 452027, 703657, 1093237,
   1695781, 2627993, 4067599, 6290467, 9718019,
   15000607, 23133937, 35650091};


int HashUtils::nextPrime(int newCapacity)
{
  TEUCHOS_TEST_FOR_EXCEPTION(newCapacity > primes_[primeCount_-1],
                     std::logic_error,
                     "HashUtils::nextPrime() overflow");

  for (int i=0; i<primeCount_; i++)
    {
      if (newCapacity <= primes_[i])
        {
          return primes_[i];
        }
    }

  TEUCHOS_TEST_FOR_EXCEPTION(true,
                     std::logic_error,
                     "unexpected case in HashUtils::nextPrime()");
  TEUCHOS_UNREACHABLE_RETURN(0);
}

int HashUtils::getHashCode(const unsigned char *a, size_t len)
{
  int total=0;
  unsigned char *to = reinterpret_cast<unsigned char *>(&total);
  int c=0;
  for (size_t i=0; i < len; i++){
    to[c++] += a[i];
    if (c == sizeof(int))
      c = 0;
  }
  if (total < 0)
  {
      /* Convert the largest -ve int to zero and -1 to
       * std::numeric_limits<int>::max()
       * */
      size_t maxIntBeforeWrap = std::numeric_limits<int>::max();
      maxIntBeforeWrap ++;
      total += maxIntBeforeWrap;
  }
  return total;
}