From 0992182965d21ce2a8c1325205923a4ecd341e40 Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Fri, 24 Feb 2017 14:51:26 +0100
Subject: Start sequential read at random offset; don't re-init prng every time

---
 src/copythread.cpp | 11 ++++++++---
 src/speedcheck.cpp |  1 +
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/copythread.cpp b/src/copythread.cpp
index 1f9ec2f..5b9710b 100644
--- a/src/copythread.cpp
+++ b/src/copythread.cpp
@@ -9,6 +9,8 @@
 // 20 seconds for each test
 #define TEST_LENGTH (60000)
 
+#define BIGRAND (qint64(qrand()) | (qint64(qrand()) * qint64(RAND_MAX)))
+
 CopyThread::CopyThread(QFile *file, QObject *parent)
 	: QThread(parent),
 	  _doStop(false)
@@ -35,8 +37,13 @@ void CopyThread::run()
 	qint64 seqSum = 0, rndSum = 0;
 	qint64 seqTime, rndTime = -1;
 
+	const qint64 size = _file->size() - BUFFER_SIZE;
+
 	// Sequential read
 	emit logMessage(trUtf8("Starting sequential read test"));
+	if (size > 0) {
+		_file->seek(BIGRAND % size);
+	}
 	timer.start();
 	do {
 		ret = _file->read(buffer, BUFFER_SIZE);
@@ -48,13 +55,11 @@ void CopyThread::run()
 	seqTime = timer.elapsed();
 
 	// Random read
-	qsrand((uint)QCoreApplication::applicationPid());
-	const qint64 size = _file->size() - BUFFER_SIZE;
 	if (size > 0) {
 		emit logMessage(trUtf8("Starting random read test"));
 		timer.restart();
 		do {
-			_file->seek(((qint64)qrand() ^ ((qint64)qrand() << 15)) % size);
+			_file->seek(BIGRAND % size);
 			ret = _file->read(buffer, BUFFER_SIZE);
 			rndSum += ret;
 		} while (!_doStop && ret > 0 && timer.elapsed() < TEST_LENGTH);
diff --git a/src/speedcheck.cpp b/src/speedcheck.cpp
index 8ff8c93..b4dd718 100644
--- a/src/speedcheck.cpp
+++ b/src/speedcheck.cpp
@@ -21,6 +21,7 @@ SpeedCheck::SpeedCheck(QString fileName)
 	connect(_ui->btnQuit, SIGNAL(clicked(bool)), this, SLOT(quitClicked(bool)));
 	_timer.setInterval(200);
 	connect(&_timer, SIGNAL(timeout()), this, SLOT(updateTimer()));
+	qsrand((uint)QCoreApplication::applicationPid());
 }
 
 SpeedCheck::~SpeedCheck()
-- 
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