Core/Hash.h

   1 //
   2 // Copyright (c) Microsoft. All rights reserved.
   3 // This code is licensed under the MIT License (MIT).
   4 // THIS CODE IS PROVIDED *AS IS* WITHOUT WARRANTY OF
   5 // ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING ANY
   6 // IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR
   7 // PURPOSE, MERCHANTABILITY, OR NON-INFRINGEMENT.
   8 //
   9 // Developed by Minigraph
  10 //
  11 // Author:  James Stanard
  12
  13 #pragma once
  14
  15 #include "Math/Common.h"
  16 #include <smmintrin.h>
  17
  18 #ifdef __SSE4_2__
  19 #define ENABLE_SSE_CRC32 1
  20 #else
  21 #define ENABLE_SSE_CRC32 0
  22 #endif
  23
  24 namespace Utility
  25 {
  26     inline size_t HashRange(const uint32_t* const Begin, const uint32_t* const End, size_t Hash)
  27     {
  28 #if ENABLE_SSE_CRC32
  29         const uint64_t* Iter64 = (const uint64_t*)Math::AlignUp(Begin, 8);
  30         const uint64_t* const End64 = (const uint64_t* const)Math::AlignDown(End, 8);
  31
  32         // If not 64-bit aligned, start with a single u32
  33         if ((uint32_t*)Iter64 > Begin)
  34             Hash = _mm_crc32_u32((uint32_t)Hash, *Begin);
  35
  36         // Iterate over consecutive u64 values
  37         while (Iter64 < End64)
  38             Hash = _mm_crc32_u64((uint64_t)Hash, *Iter64++);
  39
  40         // If there is a 32-bit remainder, accumulate that
  41         if ((uint32_t*)Iter64 < End)
  42             Hash = _mm_crc32_u32((uint32_t)Hash, *(uint32_t*)Iter64);
  43 #else
  44         // An inexpensive hash for CPUs lacking SSE4.2
  45         for (const uint32_t* Iter = Begin; Iter < End; ++Iter)
  46             Hash = 16777619U * Hash ^ *Iter;
  47 #endif
  48
  49         return Hash;
  50     }
  51
  52     template <typename T> inline size_t HashState( const T* StateDesc, size_t Count = 1, size_t Hash = 2166136261U )
  53     {
  54         static_assert((sizeof(T) & 3) == 0 && alignof(T) >= 4, "State object is not word-aligned");
  55         return HashRange((uint32_t*)StateDesc, (uint32_t*)(StateDesc + Count), Hash);
  56     }
  57
  58 } // namespace Utility