Allow to chain qt_hash() calls

There are some callers of qt_hash that first build a string just to hash it.
By allowing to pass an initial value for 'h', we can chain qt_hash() calls
to avoid having to allocate memory just to hash a two-part string.

Change-Id: Ifaca82d47b2fb8c707912342c3ddd84f91e70267
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 10 insertions, 12 deletions

diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp
index f83643e90a..662c304a2e 100644
--- a/src/corelib/tools/qhash.cpp
+++ b/src/corelib/tools/qhash.cpp
@@ -412,27 +412,25 @@ void qSetGlobalQHashSeed(int newSeed)
     results.
 
     The qt_hash functions must *never* change their results.
+
+    This function can hash discontiguous memory by invoking it on each chunk,
+    passing the previous's result in the next call's \a chained argument.
 */
-static uint qt_hash(const QChar *p, size_t n) Q_DECL_NOTHROW
+uint qt_hash(QStringView key, uint chained) Q_DECL_NOTHROW
 {
-    uint h = 0;
+    auto n = key.size();
+    auto p = key.utf16();
+
+    uint h = chained;
 
     while (n--) {
-        h = (h << 4) + (*p++).unicode();
+        h = (h << 4) + *p++;
         h ^= (h & 0xf0000000) >> 23;
         h &= 0x0fffffff;
     }
     return h;
 }
 
-/*!
-    \internal
-*/
-uint qt_hash(QStringView key) Q_DECL_NOTHROW
-{
-    return qt_hash(key.data(), key.size());
-}
-
 /*
     The prime_deltas array contains the difference between a power
     of two and the next prime number:
diff --git a/src/corelib/tools/qhashfunctions.h b/src/corelib/tools/qhashfunctions.h
index 2c3abe6af0..f75b310e4e 100644
--- a/src/corelib/tools/qhashfunctions.h
+++ b/src/corelib/tools/qhashfunctions.h
@@ -102,7 +102,7 @@ Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QStringRef &key, uint seed =
 Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(QStringView key, uint seed = 0) Q_DECL_NOTHROW;
 Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QBitArray &key, uint seed = 0) Q_DECL_NOTHROW;
 Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(QLatin1String key, uint seed = 0) Q_DECL_NOTHROW;
-Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qt_hash(QStringView key) Q_DECL_NOTHROW;
+Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qt_hash(QStringView key, uint chained = 0) Q_DECL_NOTHROW;
 
 template <class T> inline uint qHash(const T *key, uint seed = 0) Q_DECL_NOTHROW
 {