AuroraMiddleware/qt5base-lts
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Optimize hashing of floating point numbers

Browse Source 
Change-Id: Id5e091b135c006b10987f229f45319228edb8675
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
This commit is contained in:
Lars Knoll 2020-02-09 15:51:03 +01:00
parent 09bdf907cf
commit 73ddfa25b4
2 changed files with 24 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
src/corelib/tools/qhash.cpp
View File

@ -769,17 +769,12 @@ uint qt_hash(QStringView key, uint chained) noexcept
Returns the hash value for the \a key, using \a seed to seed the calculation.
*/
/*! \relates QHash
/*! \fn size_t qHash(float key, size_t seed) noexcept
\relates QHash
\since 5.3
Returns the hash value for the \a key, using \a seed to seed the calculation.
*/
size_t qHash(float key, size_t seed) noexcept
{
// ensure -0 gets mapped to 0
key += 0.0f;
return murmurhash(&key, sizeof(key), seed);
}
/*! \relates QHash
\since 5.3
@ -790,7 +785,13 @@ size_t qHash(double key, size_t seed) noexcept
{
// ensure -0 gets mapped to 0
key += 0.0;
return murmurhash(&key, sizeof(key), seed);
if constexpr (sizeof(double) == sizeof(size_t)) {
size_t k;
memcpy(&k, &key, sizeof(double));
return QHashPrivate::hash(k, seed);
} else {
return murmurhash(&key, sizeof(key), seed);
}
}
#if !defined(Q_OS_DARWIN) || defined(Q_CLANG_QDOC)
@ -803,7 +804,13 @@ size_t qHash(long double key, size_t seed) noexcept
{
// ensure -0 gets mapped to 0
key += static_cast<long double>(0.0);
return murmurhash(&key, sizeof(key), seed);
if constexpr (sizeof(long double) == sizeof(size_t)) {
size_t k;
memcpy(&k, &key, sizeof(long double));
return QHashPrivate::hash(k, seed);
} else {
return murmurhash(&key, sizeof(key), seed);
}
}
#endif

9
src/corelib/tools/qhashfunctions.h
View File

@ -120,7 +120,14 @@ Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline size_t qHash(quint64 key, size_t s
return QHashPrivate::hash(size_t(key), seed);
}
Q_DECL_CONST_FUNCTION constexpr inline size_t qHash(qint64 key, size_t seed = 0) noexcept { return qHash(quint64(key), seed); }
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION size_t qHash(float key, size_t seed = 0) noexcept;
Q_DECL_CONST_FUNCTION inline size_t qHash(float key, size_t seed = 0) noexcept
{
// ensure -0 gets mapped to 0
key += 0.0f;
uint k;
memcpy(&k, &key, sizeof(float));
return QHashPrivate::hash(k, seed);
}
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION size_t qHash(double key, size_t seed = 0) noexcept;
#if !defined(Q_OS_DARWIN) || defined(Q_CLANG_QDOC)
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION size_t qHash(long double key, size_t seed = 0) noexcept;