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, 5 insertions, 0 deletions

diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index 9dd0e6144d..d4bf8df442 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -85,6 +85,11 @@ inline uint qHash(quint64 key, uint seed = 0) Q_DECL_NOTHROW
     }
 }
 inline uint qHash(qint64 key, uint seed = 0) Q_DECL_NOTHROW { return qHash(quint64(key), seed); }
+Q_CORE_EXPORT uint qHash(float key, uint seed = 0) Q_DECL_NOTHROW;
+Q_CORE_EXPORT uint qHash(double key, uint seed = 0) Q_DECL_NOTHROW;
+#ifndef Q_OS_DARWIN
+Q_CORE_EXPORT uint qHash(long double key, uint seed = 0) Q_DECL_NOTHROW;
+#endif
 inline uint qHash(QChar key, uint seed = 0) Q_DECL_NOTHROW { return qHash(key.unicode(), seed); }
 Q_CORE_EXPORT uint qHash(const QByteArray &key, uint seed = 0) Q_DECL_NOTHROW;
 Q_CORE_EXPORT uint qHash(const QString &key, uint seed = 0) Q_DECL_NOTHROW;