1

2 /*This file is sample code pulled off the web -- NOT part of the compiled code

3 * make sure it doesn't get included in makefile 'cause it doesn't compile

4 */

5

6 //-----------------------------------------------------------------------------

7 // MurmurHash2, by Austin Appleby

8

9 // Note - This code makes a few assumptions about how your machine behaves -

10

11 // 1. We can read a 4-byte value from any address without crashing

12 // 2. sizeof(int) == 4

13

14 // And it has a few limitations -

15

16 // 1. It will not work incrementally.

17 // 2. It will not produce the same results on little-endian and big-endian

18 // machines.

19

20 unsigned int MurmurHash2 ( const void * key, int len, unsigned int seed )

21 {

22 // 'm' and 'r' are mixing constants generated offline.

23 // They're not really 'magic', they just happen to work well.

24

25 const unsigned int m = 0x5bd1e995;

26 const int r = 24;

27

28 // Initialize the hash to a 'random' value

29

30 unsigned int h = seed ^ len;

31

32 // Mix 4 bytes at a time into the hash

33

34 const unsigned char * data = (const unsigned char *)key;

35

36 while(len >= 4)

37 {

38 unsigned int k = *(unsigned int *)data;

39

40 k *= m;

41 k ^= k >> r;

42 k *= m;

43

44 h *= m;

45 h ^= k;

46

47 data += 4;

48 len -= 4;

49 }

50

51 // Handle the last few bytes of the input array

52

53 switch(len)

54 {

55 case 3: h ^= data[2] << 16;

56 case 2: h ^= data[1] << 8;

57 case 1: h ^= data[0];

58 h *= m;

59 };

60

61 // Do a few final mixes of the hash to ensure the last few

62 // bytes are well-incorporated.

63

64 h ^= h >> 13;

65 h *= m;

66 h ^= h >> 15;

67

68 return h;

69 }