From c0791ac76ec7cfdc3945efa67a6f72ee3623413c Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@kdab.com>
Date: Wed, 12 Feb 2014 14:18:40 +0100
Subject: [PATCH] Add qHash() overloads for floating-point types
MIME-Version: 1.0
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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>
---
 src/corelib/tools/qhash.cpp                  | 32 ++++++++++++++++++++
 src/corelib/tools/qhash.h                    |  5 +++
 tests/auto/corelib/tools/qhash/tst_qhash.cpp | 15 +++++++++
 3 files changed, 52 insertions(+)

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
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;
diff --git a/tests/auto/corelib/tools/qhash/tst_qhash.cpp b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
index af1c7aed15..ddb72a3c32 100644
--- a/tests/auto/corelib/tools/qhash/tst_qhash.cpp
+++ b/tests/auto/corelib/tools/qhash/tst_qhash.cpp
@@ -64,6 +64,7 @@ private slots:
     void rehash_isnt_quadratic();
     void dont_need_default_constructor();
     void qhash();
+    void fp_qhash_of_zero_is_zero();
     void qmultihash_specific();
 
     void compare();
@@ -1043,6 +1044,20 @@ void tst_QHash::qhash()
     }
 }
 
+void tst_QHash::fp_qhash_of_zero_is_zero()
+{
+    QCOMPARE(qHash(-0.0f), 0U);
+    QCOMPARE(qHash( 0.0f), 0U);
+
+    QCOMPARE(qHash(-0.0 ), 0U);
+    QCOMPARE(qHash( 0.0 ), 0U);
+
+#ifndef Q_OS_DARWIN
+    QCOMPARE(qHash(-0.0L), 0U);
+    QCOMPARE(qHash( 0.0L), 0U);
+#endif
+}
+
 void tst_QHash::qmultihash_specific()
 {
     QMultiHash<int, int> hash1;