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faster std::hash<uuid> implementation

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This commit is contained in:
Marius Bancila 2021-12-23 01:00:23 +02:00
parent 8e9d0f87f5
commit 5458877f2c
2 changed files with 37 additions and 0 deletions
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33
include/uuid.h
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@ -526,6 +526,8 @@ namespace uuids
template<class CharT, class Traits, class Allocator>
friend std::basic_string<CharT, Traits, Allocator> to_string(uuid const& id);
friend std::hash<uuid>;
};
// --------------------------------------------------------------------------------------------------------------------------
@ -922,8 +924,39 @@ namespace std
result_type operator()(argument_type const &uuid) const
{
#ifdef UUID_HASH_STRING_BASED
std::hash<std::string> hasher;
return static_cast<result_type>(hasher(uuids::to_string(uuid)));
#else
uint64_t l =
static_cast<uint64_t>(uuid.data[0]) << 56 |
static_cast<uint64_t>(uuid.data[1]) << 48 |
static_cast<uint64_t>(uuid.data[2]) << 40 |
static_cast<uint64_t>(uuid.data[3]) << 32 |
static_cast<uint64_t>(uuid.data[4]) << 24 |
static_cast<uint64_t>(uuid.data[5]) << 16 |
static_cast<uint64_t>(uuid.data[6]) << 8 |
static_cast<uint64_t>(uuid.data[7]);
uint64_t h =
static_cast<uint64_t>(uuid.data[8]) << 56 |
static_cast<uint64_t>(uuid.data[9]) << 48 |
static_cast<uint64_t>(uuid.data[10]) << 40 |
static_cast<uint64_t>(uuid.data[11]) << 32 |
static_cast<uint64_t>(uuid.data[12]) << 24 |
static_cast<uint64_t>(uuid.data[13]) << 16 |
static_cast<uint64_t>(uuid.data[14]) << 8 |
static_cast<uint64_t>(uuid.data[15]);
if (sizeof(result_type) > 4)
{
return result_type(l ^ h);
}
else
{
uint64_t hash64 = l ^ h;
return result_type(uint32_t(hash64 >> 32) ^ uint32_t(hash64));
}
#endif
}
};
}

4
test/test_uuid.cpp
View File

@ -525,7 +525,11 @@ TEST_CASE("Test hashing", "[ops]")
auto h1 = std::hash<std::string>{};
auto h2 = std::hash<uuid>{};
#ifdef UUID_HASH_STRING_BASED
REQUIRE(h1(str) == h2(guid));
#else
REQUIRE(h1(str) != h2(guid));
#endif
auto engine = uuids::uuid_random_generator::engine_type{};
seed_rng(engine);