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Utilities - Tuple hash computations

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This commit is contained in:
Emmanuel BENOîT 2020-09-26 11:14:14 +02:00
parent 3889efde67
commit 8a19374d3f
2 changed files with 77 additions and 3 deletions
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36
include/ebcl/inline/Utilities.hh
View file

@ -376,6 +376,42 @@ inline uint32_t ComputeHash( std::pair< T1 , T2 > const& item )
return hv; return hv;
} }
// Recursive template that will hash each tuple element starting from
// the last one.
template< typename Tuple , size_t Index = std::tuple_size< Tuple >::value - 1 >
struct T_TupleHashHelper_
{
static void apply( uint32_t& hashValue , Tuple const& t )
{
T_TupleHashHelper_< Tuple , Index - 1 >::apply( hashValue , t );
CombineHash( hashValue , std::get< Index >( t ) );
}
};
// Specialize for the first element, as it must not recurse.
template< typename Tuple >
struct T_TupleHashHelper_< Tuple , 0 >
{
static void apply( uint32_t& hashValue , Tuple const& t )
{
CombineHash( hashValue , std::get< 0 >( t ) );
}
};
template< typename... Types >
inline uint32_t ComputeHash( std::tuple< Types... > const& item )
{
uint32_t hv = 0;
T_TupleHashHelper_< std::tuple< Types... > >::apply( hv , item );
return hv;
}
// Specialize the function for empty tuples
template< >
inline uint32_t ComputeHash( std::tuple< > const& )
{
return 0;
}
/*= PRIVATE IMPLEMENTATION BASE ==============================================*/ /*= PRIVATE IMPLEMENTATION BASE ==============================================*/

44
tests/hash-functions.cc
View file

@ -14,6 +14,11 @@ class ComputeHashTest : public CppUnit::TestFixture
CPPUNIT_TEST( testInt64 ); CPPUNIT_TEST( testInt64 );
CPPUNIT_TEST( testStructDefault ); CPPUNIT_TEST( testStructDefault );
CPPUNIT_TEST( testPair ); CPPUNIT_TEST( testPair );
CPPUNIT_TEST( testTupleEmpty );
CPPUNIT_TEST( testTupleOne );
CPPUNIT_TEST( testTuplePair );
CPPUNIT_TEST( testTupleMore );
CPPUNIT_TEST_SUITE_END( ); CPPUNIT_TEST_SUITE_END( );
public: public:
@ -23,6 +28,11 @@ public:
void testInt64( ); void testInt64( );
void testStructDefault( ); void testStructDefault( );
void testPair( ); void testPair( );
void testTupleEmpty( );
void testTupleOne( );
void testTuplePair( );
void testTupleMore( );
}; };
@ -79,10 +89,38 @@ void ComputeHashTest::testStructDefault( )
void ComputeHashTest::testPair( ) void ComputeHashTest::testPair( )
{ {
auto p{ std::make_pair< uint8_t , uint32_t >( 12 , 128 ) }; const auto p{ std::make_pair< uint8_t , uint32_t >( 12 , 128 ) };
uint32_t hv = 0x9e3779b9 + 12; uint32_t hv = 0x9e3779b9 + 12;
hv = 128 + 0x9e3779b9 + ( hv << 6 ) + ( hv >> 2 ); hv = 128 + 0x9e3779b9 + ( hv << 6 ) + ( hv >> 2 );
CPPUNIT_ASSERT_EQUAL( hv , ComputeHash( p ) ); CPPUNIT_ASSERT_EQUAL( hv , ComputeHash( p ) );
} }
/*----------------------------------------------------------------------------*/
void ComputeHashTest::testTupleEmpty( )
{
const std::tuple< > t{};
CPPUNIT_ASSERT_EQUAL( 0u , ComputeHash( t ) );
}
void ComputeHashTest::testTupleOne( )
{
const std::tuple< uint8_t > t{ 12 };
CPPUNIT_ASSERT_EQUAL( 0x9e3779b9 + 12u , ComputeHash( t ) );
}
void ComputeHashTest::testTuplePair( )
{
const auto p{ std::make_pair< uint8_t , uint32_t >( 12 , 128 ) };
const auto t{ std::make_tuple< uint8_t , uint32_t >( 12 , 128 ) };
CPPUNIT_ASSERT_EQUAL( ComputeHash( p ) , ComputeHash( t ) );
}
void ComputeHashTest::testTupleMore( )
{
const auto p{ std::make_pair< uint8_t , uint32_t >( 12 , 128 ) };
const auto t{ std::make_tuple< uint8_t , uint32_t , uint8_t >( 12 , 128 , 92 ) };
uint32_t hv = ComputeHash( p );
CombineHash( hv , uint8_t( 92 ) );
CPPUNIT_ASSERT_EQUAL( hv , ComputeHash( t ) );
}