|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
#ifndef CondCommon_Hash64_h
#define CondCommon_Hash64_h
namespace cond {
/*
--------------------------------------------------------------------
lookup8.c, by Bob Jenkins, January 4 1997, Public Domain.
hash(), hash2(), hash3, and mix() are externally useful functions.
Routines to test the hash are included if SELF_TEST is defined.
You can use this free for any purpose. It has no warranty.
--------------------------------------------------------------------
*/
/*
--------------------------------------------------------------------
hash() -- hash a variable-length key into a 64-bit value
k : the key (the unaligned variable-length array of bytes)
len : the length of the key, counting by bytes
level : can be any 8-byte value
Returns a 64-bit value. Every bit of the key affects every bit of
the return value. No funnels. Every 1-bit and 2-bit delta achieves
avalanche. About 41+5len instructions.
The best hash table sizes are powers of 2. There is no need to do
mod a prime (mod is sooo slow!). If you need less than 64 bits,
use a bitmask. For example, if you need only 10 bits, do
h = (h & hashmask(10));
In which case, the hash table should have hashsize(10) elements.
If you are hashing n strings (ub1 **)k, do it like this:
for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
By Bob Jenkins, Jan 4 1997. bob_jenkins@burtleburtle.net. You may
use this code any way you wish, private, educational, or commercial,
but I would appreciate if you give me credit.
See http://burtleburtle.net/bob/hash/evahash.html
Use for hash table lookup, or anything where one collision in 2^^64
is acceptable. Do NOT use for cryptographic purposes.
--------------------------------------------------------------------
*/
/*
--------------------------------------------------------------------
This is identical to hash() on little-endian machines, and it is much
faster than hash(), but a little slower than hash2(), and it requires
-- that all your machines be little-endian, for example all Intel x86
chips or all VAXen. It gives wrong results on big-endian machines.
--------------------------------------------------------------------
*/
unsigned long long hash64(unsigned char* k, unsigned long long length, unsigned long long level);
} // namespace cond
#endif
|