Add qHash() overloads for floating-point types

This implementation is based on GCC's implementation of std::hash<FP>, but only
to the extent of checking for zero before hashing the bits. The bit hasher is
the Qt one; I didn't even look what GCC uses.

The check against 0.0 is mandated by the requirement to have
  \forall x,y: x == y => qHash(x) == qHash(y)
which would be violated for x = 0.0 and y = -0.0 if we only hashed the bits.

Implemented out-of-line to avoid potential FP-comparison warnings, as well
as to be able to use the file-static hash() functions, which gets inlined
unlike qHashBits(), which cannot be.

[ChangeLog][QtCore][QHash/QSet] Allowed to use float, double and long double
as QHash/QSet keys.

Change-Id: I38cec4afb860f17e9f8be7b67544e58b330f8fff
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp
index 18d1cee0eb..5320ea1fbf 100644
--- a/src/corelib/tools/qhash.cpp
+++ b/src/corelib/tools/qhash.cpp
@@ -737,6 +737,38 @@ void QHashData::checkSanity()
     Returns the hash value for the \a key, using \a seed to seed the calculation.
 */
 
+/*! \relates QHash
+    \since 5.3
+
+    Returns the hash value for the \a key, using \a seed to seed the calculation.
+*/
+uint qHash(float key, uint seed) Q_DECL_NOTHROW
+{
+    return key != 0.0f ? hash(reinterpret_cast<const uchar *>(&key), sizeof(key), seed) : seed ;
+}
+
+/*! \relates QHash
+    \since 5.3
+
+    Returns the hash value for the \a key, using \a seed to seed the calculation.
+*/
+uint qHash(double key, uint seed) Q_DECL_NOTHROW
+{
+    return key != 0.0  ? hash(reinterpret_cast<const uchar *>(&key), sizeof(key), seed) : seed ;
+}
+
+#ifndef Q_OS_DARWIN
+/*! \relates QHash
+    \since 5.3
+
+    Returns the hash value for the \a key, using \a seed to seed the calculation.
+*/
+uint qHash(long double key, uint seed) Q_DECL_NOTHROW
+{
+    return key != 0.0L ? hash(reinterpret_cast<const uchar *>(&key), sizeof(key), seed) : seed ;
+}
+#endif
+
 /*! \fn uint qHash(QChar key, uint seed = 0)
     \relates QHash
     \since 5.0