OpenCAX/entry/src/main/cpp/include/opencascade/Standard_HashUtils.lxx

// Copyright (c) 2023 OPEN CASCADE SAS
//
// This file is part of Open CASCADE Technology software library.
//
// This library is free software; you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License version 2.1 as published
// by the Free Software Foundation, with special exception defined in the file
// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
// distribution for complete text of the license and disclaimer of any warranty.
//
// Alternatively, this file may be used under the terms of Open CASCADE
// commercial license or contractual agreement.

#include <cstring>

namespace opencascade
{
namespace MurmurHash
{
namespace MurmurHashUtils
{
inline uint64_t shift_mix(uint64_t theV)
{
  return theV ^ (theV >> 47);
}

// Loads n bytes, where 1 <= n < 8.
inline uint64_t load_bytes(const char* thePnt, int theNb)
{
  uint64_t aRes = 0;
  --theNb;
  do
    aRes = (aRes << 8) + static_cast<unsigned char>(thePnt[theNb]);
  while (--theNb >= 0);
  return aRes;
}

template <typename T>
inline T unaligned_load(const char* thePnt)
{
  T aRes;
  memcpy(&aRes, thePnt, sizeof(aRes));
  return aRes;
}
} // namespace MurmurHashUtils

//=======================================================================
// function : MurmurHash64A
// purpose  :
//=======================================================================
inline uint64_t MurmurHash64A(const void* theKey, int theLen, uint64_t theSeed)
{
  static constexpr uint64_t aMul = (((uint64_t)0xc6a4a793UL) << 32UL) + (uint64_t)0x5bd1e995UL;
  const char* const         aBuf = static_cast<const char*>(theKey);

  // Remove the bytes not divisible by the sizeof(uint64_t).  This
  // allows the main loop to process the data as 64-bit integers.
  const uint64_t    aLenAligned = theLen & ~(uint64_t)0x7;
  const char* const anEnd       = aBuf + aLenAligned;
  uint64_t          aHash       = theSeed ^ (theLen * aMul);
  for (const char* aPnt = aBuf; aPnt != anEnd; aPnt += 8)
  {
    const uint64_t aData =
      MurmurHashUtils::shift_mix(MurmurHashUtils::unaligned_load<uint64_t>(aPnt) * aMul) * aMul;
    aHash ^= aData;
    aHash *= aMul;
  }
  if ((theLen & 0x7) != 0)
  {
    const uint64_t data = MurmurHashUtils::load_bytes(anEnd, theLen & 0x7);
    aHash ^= data;
    aHash *= aMul;
  }
  aHash = MurmurHashUtils::shift_mix(aHash) * aMul;
  aHash = MurmurHashUtils::shift_mix(aHash);
  return aHash;
}

//=======================================================================
// function : MurmurHash2A
// purpose  :
//=======================================================================
inline uint32_t MurmurHash2A(const void* theKey, int theLen, uint32_t theSeed)
{
  const uint32_t aMul  = 0x5bd1e995;
  uint32_t       aHash = theSeed ^ theLen;
  const char*    aBuf  = static_cast<const char*>(theKey);

  // Mix 4 bytes at a time into the hash.
  while (theLen >= 4)
  {
    uint32_t aKey = MurmurHashUtils::unaligned_load<uint32_t>(aBuf);
    aKey *= aMul;
    aKey ^= aKey >> 24;
    aKey *= aMul;
    aHash *= aMul;
    aHash ^= aKey;
    aBuf += 4;
    theLen -= 4;
  }

  uint32_t aKey;
  // Handle the last few bytes of the input array.
  switch (theLen)
  {
    case 3:
      aKey = static_cast<unsigned char>(aBuf[2]);
      aHash ^= aKey << 16;
      Standard_FALLTHROUGH
    case 2:
      aKey = static_cast<unsigned char>(aBuf[1]);
      aHash ^= aKey << 8;
      Standard_FALLTHROUGH
    case 1:
      aKey = static_cast<unsigned char>(aBuf[0]);
      aHash ^= aKey;
      aHash *= aMul;
  };

  // Do a few final mixes of the hash.
  aHash ^= aHash >> 13;
  aHash *= aMul;
  aHash ^= aHash >> 15;
  return aHash;
}
} // namespace MurmurHash

namespace FNVHash
{
//=======================================================================
// function : FNVHash1A
// purpose  :
//=======================================================================
inline uint32_t FNVHash1A(const void* theKey, int theLen, uint32_t theSeed)
{
  const char* cptr = static_cast<const char*>(theKey);
  for (; theLen; --theLen)
  {
    theSeed ^= static_cast<uint32_t>(*cptr++);
    theSeed *= static_cast<uint32_t>(16777619UL);
  }
  return theSeed;
}

//=======================================================================
// function : FNVHash64A
// purpose  :
//=======================================================================
inline uint64_t FNVHash64A(const void* theKey, int theLen, uint64_t theSeed)
{
  const char* cptr = static_cast<const char*>(theKey);
  for (; theLen; --theLen)
  {
    theSeed ^= static_cast<uint64_t>(*cptr++);
    theSeed *= static_cast<uint64_t>(1099511628211ULL);
  }
  return theSeed;
}
} // namespace FNVHash
} // namespace opencascade