dmd.root.hash source code

1 /**
2  * Hash functions for arbitrary binary data.
3  *
4  * Copyright: Copyright (C) 1999-2020 by The D Language Foundation, All Rights Reserved
5  * Authors:   Martin Nowak, Walter Bright, http://www.digitalmars.com
6  * License:   $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
7  * Source:    $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/root/hash.d, root/_hash.d)
8  * Documentation:  https://dlang.org/phobos/dmd_root_hash.html
9  * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/root/hash.d
10  */
11 
12 module dmd.root.hash;
13 
14 // MurmurHash2 was written by Austin Appleby, and is placed in the public
15 // domain. The author hereby disclaims copyright to this source code.
16 // https://sites.google.com/site/murmurhash/
17 uint calcHash(scope const(char)[] data) @nogc nothrow pure @safe
18 {
19     return calcHash(cast(const(ubyte)[])data);
20 }
21 
22 /// ditto
23 uint calcHash(scope const(ubyte)[] data) @nogc nothrow pure @safe
24 {
25     // 'm' and 'r' are mixing constants generated offline.
26     // They're not really 'magic', they just happen to work well.
27     enum uint m = 0x5bd1e995;
28     enum int r = 24;
29     // Initialize the hash to a 'random' value
30     uint h = cast(uint) data.length;
31     // Mix 4 bytes at a time into the hash
32     while (data.length >= 4)
33     {
34         uint k = data[3] << 24 | data[2] << 16 | data[1] << 8 | data[0];
35         k *= m;
36         k ^= k >> r;
37         h = (h * m) ^ (k * m);
38         data = data[4..$];
39     }
40     // Handle the last few bytes of the input array
41     switch (data.length & 3)
42     {
43     case 3:
44         h ^= data[2] << 16;
45         goto case;
46     case 2:
47         h ^= data[1] << 8;
48         goto case;
49     case 1:
50         h ^= data[0];
51         h *= m;
52         goto default;
53     default:
54         break;
55     }
56     // Do a few final mixes of the hash to ensure the last few
57     // bytes are well-incorporated.
58     h ^= h >> 13;
59     h *= m;
60     h ^= h >> 15;
61     return h;
62 }
63 
64 unittest
65 {
66     char[10] data = "0123456789";
67     assert(calcHash(data[0..$]) ==   439_272_720);
68     assert(calcHash(data[1..$]) == 3_704_291_687);
69     assert(calcHash(data[2..$]) == 2_125_368_748);
70     assert(calcHash(data[3..$]) == 3_631_432_225);
71 }
72 
73 // combine and mix two words (boost::hash_combine)
74 size_t mixHash(size_t h, size_t k) @nogc nothrow pure @safe
75 {
76     return h ^ (k + 0x9e3779b9 + (h << 6) + (h >> 2));
77 }
78 
79 unittest
80 {
81     // & uint.max because mixHash output is truncated on 32-bit targets
82     assert((mixHash(0xDE00_1540, 0xF571_1A47) & uint.max) == 0x952D_FC10);
83 }