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             : //-----------------------------------------------------------------------------
      19             : // Platform-specific functions and macros
      20             : 
      21             : // Microsoft Visual Studio
      22             : 
      23             : #if defined(_MSC_VER)
      24             : 
      25             : #define BIG_CONSTANT(x) (x)
      26             : 
      27             : // Other compilers
      28             : 
      29             : #else   // defined(_MSC_VER)
      30             : 
      31             : #define BIG_CONSTANT(x) (x##LLU)
      32             : 
      33             : #endif // !defined(_MSC_VER)
      34             : 
      35             : //-----------------------------------------------------------------------------
      36             : 
      37          11 : uint32_t MurmurHash2 ( const void * key, int len, uint32_t seed )
      38             : {
      39             :   // 'm' and 'r' are mixing constants generated offline.
      40             :   // They're not really 'magic', they just happen to work well.
      41             : 
      42          11 :   const uint32_t m = 0x5bd1e995;
      43          11 :   const int r = 24;
      44             : 
      45             :   // Initialize the hash to a 'random' value
      46             : 
      47          11 :   uint32_t h = seed ^ len;
      48             : 
      49             :   // Mix 4 bytes at a time into the hash
      50             : 
      51          11 :   const unsigned char * data = (const unsigned char *)key;
      52             : 
      53          32 :   while(len >= 4)
      54             :   {
      55          10 :     uint32_t k = *(uint32_t*)data;
      56             : 
      57          10 :     k *= m;
      58          10 :     k ^= k >> r;
      59          10 :     k *= m;
      60             : 
      61          10 :     h *= m;
      62          10 :     h ^= k;
      63             : 
      64          10 :     data += 4;
      65          10 :     len -= 4;
      66             :   }
      67             : 
      68             :   // Handle the last few bytes of the input array
      69             : 
      70          11 :   switch(len)
      71             :   {
      72          11 :   case 3: h ^= data[2] << 16;
      73          11 :   case 2: h ^= data[1] << 8;
      74          11 :   case 1: h ^= data[0];
      75          11 :       h *= m;
      76             :   };
      77             : 
      78             :   // Do a few final mixes of the hash to ensure the last few
      79             :   // bytes are well-incorporated.
      80             : 
      81          11 :   h ^= h >> 13;
      82          11 :   h *= m;
      83          11 :   h ^= h >> 15;
      84             : 
      85          11 :   return h;
      86             : }