Line data    Source code

       1             : //-----------------------------------------------------------------------------
       2             : // MurmurHash2 was written by Austin Appleby, and is placed in the public
       3             : // domain. The author hereby disclaims copyright to this source code.
       4             : 
       5             : // Note - This code makes a few assumptions about how your machine behaves -
       6             : 
       7             : // 1. We can read a 4-byte value from any address without crashing
       8             : // 2. sizeof(int) == 4
       9             : 
      10             : // And it has a few limitations -
      11             : 
      12             : // 1. It will not work incrementally.
      13             : // 2. It will not produce the same results on little-endian and big-endian
      14             : //    machines.
      15             : 
      16             : #include "MurmurHash2.h"
      17             : 
      18             : #if __GNUC__ >= 7
      19             : _Pragma("GCC diagnostic ignored \"-Wimplicit-fallthrough\"")
      20             : #endif
      21             : 
      22             : //-----------------------------------------------------------------------------
      23             : // Platform-specific functions and macros
      24             : 
      25             : // Microsoft Visual Studio
      26             : 
      27             : #if defined(_MSC_VER)
      28             : 
      29             : #define BIG_CONSTANT(x) (x)
      30             : 
      31             : // Other compilers
      32             : 
      33             : #else        // defined(_MSC_VER)
      34             : 
      35             : #define BIG_CONSTANT(x) (x##LLU)
      36             : 
      37             : #endif // !defined(_MSC_VER)
      38             : 
      39             : //-----------------------------------------------------------------------------
      40             : 
      41          12 : uint32_t MurmurHash2 ( const void * key, int len, uint32_t seed )
      42             : {
      43             :   // 'm' and 'r' are mixing constants generated offline.
      44             :   // They're not really 'magic', they just happen to work well.
      45             : 
      46          12 :   const uint32_t m = 0x5bd1e995;
      47          12 :   const int r = 24;
      48             : 
      49             :   // Initialize the hash to a 'random' value
      50             : 
      51          12 :   uint32_t h = seed ^ len;
      52             : 
      53             :   // Mix 4 bytes at a time into the hash
      54             : 
      55          12 :   const unsigned char * data = (const unsigned char *)key;
      56             : 
      57          23 :   while (len >= 4)
      58             :   {
      59          11 :     uint32_t k = *(uint32_t*)data;
      60             : 
      61          11 :     k *= m;
      62          11 :     k ^= k >> r;
      63          11 :     k *= m;
      64             : 
      65          11 :     h *= m;
      66          11 :     h ^= k;
      67             : 
      68          11 :     data += 4;
      69          11 :     len -= 4;
      70             :   }
      71             : 
      72             :   // Handle the last few bytes of the input array
      73             : 
      74          12 :   switch(len)
      75             :   {
      76          12 :   case 3: h ^= data[2] << 16; /* fall through */
      77          12 :   case 2: h ^= data[1] << 8;  /* fall through */
      78          12 :   case 1: h ^= data[0];       /* fall through */
      79          12 :       h *= m;
      80             :   };
      81             : 
      82             :   // Do a few final mixes of the hash to ensure the last few
      83             :   // bytes are well-incorporated.
      84             : 
      85          12 :   h ^= h >> 13;
      86          12 :   h *= m;
      87          12 :   h ^= h >> 15;
      88             : 
      89          12 :   return h;
      90             : }