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/**
* Hash functions for arbitrary binary data.
*
* Copyright: Copyright (C) 1999-2021 by The D Language Foundation, All Rights Reserved
* Authors: Martin Nowak, Walter Bright, http://www.digitalmars.com
* License: $(LINK2 http://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);
}
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