gcc/d/dmd/root/hash.d

   1 /**
   2  * Hash functions for arbitrary binary data.
   3  *
   4  * Copyright: Copyright (C) 1999-2024 by The D Language Foundation, All Rights Reserved
   5  * Authors:   Martin Nowak, Walter Bright, https://www.digitalmars.com
   6  * License:   $(LINK2 https://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 }