Add qHashRange and qHashRangeCommutative

qHashRange() takes an (input iterator) range and hashes each element, combining
the hash values using the hash combiner from Boost/N1837 with the magic number
0x9e3779b9, as described here:
http://stackoverflow.com/questions/4948780/magic-number-in-boosthash-combine

qHashRangeCommutative() does the same but with a cummutative combiner (unsigned
addition) to create hash values that are order-independent, e.g. for hashed
containers. The obvious combiner, XOR, is a bad one because it eliminates
duplicate elements. Signed addition cannot be used, since signed overflow
leads to undefined behavior.

[ChangeLog][QtCore] Added qHashRange() and qHashRangeCommutative() functions to aid
implementing qHash() overloads for custom types.

Change-Id: I3c2bbc9ce4bd0455262a70e0cf248486525e534f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/corelib/doc/snippets/code/src_corelib_tools_qhash.cpp b/src/corelib/doc/snippets/code/src_corelib_tools_qhash.cpp
index aa0473964c..0195b07b54 100644
--- a/src/corelib/doc/snippets/code/src_corelib_tools_qhash.cpp
+++ b/src/corelib/doc/snippets/code/src_corelib_tools_qhash.cpp
@@ -307,3 +307,17 @@ inline uint qHash(const std::vector<int> &key, uint seed = 0)
         return qHashBits(&key.front(), key.size() * sizeof(int), seed);
 }
 //! [qhashbits]
+
+//! [qhashrange]
+inline uint qHash(const std::vector<int> &key, uint seed = 0)
+{
+    return qHashRange(key.begin(), key.end(), seed);
+}
+//! [qhashrange]
+
+//! [qhashrangecommutative]
+inline uint qHash(const std::unordered_set<int> &key, uint seed = 0)
+{
+    return qHashRangeCommutative(key.begin(), key.end(), seed);
+}
+//! [qhashrangecommutative]