| /** |
| * Hash functions for arbitrary binary data. |
| * |
| * Copyright: Copyright (C) 1999-2023 by The D Language Foundation, All Rights Reserved |
| * Authors: Martin Nowak, Walter Bright, https://www.digitalmars.com |
| * License: $(LINK2 https://www.boost.org/LICENSE_1_0.txt, Boost License 1.0) |
| * Source: $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/root/hash.d, root/_hash.d) |
| * Documentation: https://dlang.org/phobos/dmd_root_hash.html |
| * Coverage: https://codecov.io/gh/dlang/dmd/src/master/src/dmd/root/hash.d |
| */ |
| |
| module dmd.root.hash; |
| |
| // MurmurHash2 was written by Austin Appleby, and is placed in the public |
| // domain. The author hereby disclaims copyright to this source code. |
| // https://sites.google.com/site/murmurhash/ |
| uint calcHash(scope const(char)[] data) @nogc nothrow pure @safe |
| { |
| return calcHash(cast(const(ubyte)[])data); |
| } |
| |
| /// ditto |
| uint calcHash(scope const(ubyte)[] data) @nogc nothrow pure @safe |
| { |
| // 'm' and 'r' are mixing constants generated offline. |
| // They're not really 'magic', they just happen to work well. |
| enum uint m = 0x5bd1e995; |
| enum int r = 24; |
| // Initialize the hash to a 'random' value |
| uint h = cast(uint) data.length; |
| // Mix 4 bytes at a time into the hash |
| while (data.length >= 4) |
| { |
| uint k = data[3] << 24 | data[2] << 16 | data[1] << 8 | data[0]; |
| k *= m; |
| k ^= k >> r; |
| h = (h * m) ^ (k * m); |
| data = data[4..$]; |
| } |
| // Handle the last few bytes of the input array |
| switch (data.length & 3) |
| { |
| case 3: |
| h ^= data[2] << 16; |
| goto case; |
| case 2: |
| h ^= data[1] << 8; |
| goto case; |
| case 1: |
| h ^= data[0]; |
| h *= m; |
| goto default; |
| default: |
| break; |
| } |
| // Do a few final mixes of the hash to ensure the last few |
| // bytes are well-incorporated. |
| h ^= h >> 13; |
| h *= m; |
| h ^= h >> 15; |
| return h; |
| } |
| |
| unittest |
| { |
| char[10] data = "0123456789"; |
| assert(calcHash(data[0..$]) == 439_272_720); |
| assert(calcHash(data[1..$]) == 3_704_291_687); |
| assert(calcHash(data[2..$]) == 2_125_368_748); |
| assert(calcHash(data[3..$]) == 3_631_432_225); |
| } |
| |
| // combine and mix two words (boost::hash_combine) |
| size_t mixHash(size_t h, size_t k) @nogc nothrow pure @safe |
| { |
| return h ^ (k + 0x9e3779b9 + (h << 6) + (h >> 2)); |
| } |
| |
| unittest |
| { |
| // & uint.max because mixHash output is truncated on 32-bit targets |
| assert((mixHash(0xDE00_1540, 0xF571_1A47) & uint.max) == 0x952D_FC10); |
| } |