From 8060dd3c42982543b2b5949187fa5b5bb6aeff29 Mon Sep 17 00:00:00 2001
From: Robin Burchell <robin.burchell@collabora.com>
Date: Wed, 18 Jan 2012 18:02:24 +0200
Subject: Add a string hash implementation similar to the one in Java.

This uses a similar runtime to the approach of sampling part of the string, with
the benefit that it doesn't reduce the sampling to subsections of the string.

Ironically, Java used to only sample parts of the string as well, but found that
it produced too many collisions with certain string types, so they moved to use
this method.

RESULT : tst_QHash::qhash_qt4():
     0.0537 msecs per iteration (total: 110, iterations: 2048)
PASS   : tst_QHash::qhash_qt4()
RESULT : tst_QHash::qhash_faster():
     0.015 msecs per iteration (total: 62, iterations: 4096)
PASS   : tst_QHash::qhash_faster()
RESULT : tst_QHash::javaString():
     0.016 msecs per iteration (total: 66, iterations: 4096)

Change-Id: Icb5da341ab6445163f4217650a0bdb3903e50210
Reviewed-by: hjk <qthjk@ovi.com>
---
 tests/benchmarks/corelib/tools/qhash/outofline.cpp    | 13 +++++++++++++
 tests/benchmarks/corelib/tools/qhash/qhash_string.cpp | 16 ++++++++++++++++
 tests/benchmarks/corelib/tools/qhash/qhash_string.h   | 12 ++++++++++++
 3 files changed, 41 insertions(+)

(limited to 'tests/benchmarks/corelib/tools/qhash')

diff --git a/tests/benchmarks/corelib/tools/qhash/outofline.cpp b/tests/benchmarks/corelib/tools/qhash/outofline.cpp
index 11a5f9e733..86e92e1630 100644
--- a/tests/benchmarks/corelib/tools/qhash/outofline.cpp
+++ b/tests/benchmarks/corelib/tools/qhash/outofline.cpp
@@ -87,4 +87,17 @@ uint qHash(const String &str)
     return h;
 }
 
+uint qHash(const JavaString &str)
+{
+    const unsigned short *p = (unsigned short *)str.constData();
+    const int len = str.size();
+
+    uint h = 0;
+
+    for (int i = 0; i < len; ++i)
+        h = 31 * h + p[i];
+
+    return h;
+}
+
 QT_END_NAMESPACE
diff --git a/tests/benchmarks/corelib/tools/qhash/qhash_string.cpp b/tests/benchmarks/corelib/tools/qhash/qhash_string.cpp
index 874a0c543a..4ed5a78a32 100644
--- a/tests/benchmarks/corelib/tools/qhash/qhash_string.cpp
+++ b/tests/benchmarks/corelib/tools/qhash/qhash_string.cpp
@@ -83,6 +83,7 @@ class tst_QHash : public QObject
 private slots:
     void qhash_qt4();
     void qhash_faster();
+    void javaString();
 
 private:
     QString data();
@@ -126,6 +127,21 @@ void tst_QHash::qhash_faster()
     }
 }
 
+void tst_QHash::javaString()
+{
+    QList<JavaString> items;
+    foreach (const QString &s, data().split(QLatin1Char('\n')))
+        items.append(s);
+    QHash<JavaString, int> hash;
+
+    QBENCHMARK {
+        for (int i = 0, n = items.size(); i != n; ++i) {
+            hash[items.at(i)] = i;
+        }
+    }
+}
+
+
 QTEST_MAIN(tst_QHash)
 
 #include "qhash_string.moc"
diff --git a/tests/benchmarks/corelib/tools/qhash/qhash_string.h b/tests/benchmarks/corelib/tools/qhash/qhash_string.h
index 94f142914b..3b2237e0b9 100644
--- a/tests/benchmarks/corelib/tools/qhash/qhash_string.h
+++ b/tests/benchmarks/corelib/tools/qhash/qhash_string.h
@@ -50,3 +50,15 @@ struct String : QString
 QT_BEGIN_NAMESPACE
 uint qHash(const String &);
 QT_END_NAMESPACE
+
+
+struct JavaString : QString
+{
+    JavaString() {}
+    JavaString(const QString &s) : QString(s) {}
+};
+
+QT_BEGIN_NAMESPACE
+uint qHash(const JavaString &);
+QT_END_NAMESPACE
+
-- 
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