new qRandomUuid() function

benchmark result:
********* Start testing of tst_bench_QUuid *********
Config: Using QTest library 4.12.0, Katie 4.12.0
PASS  : tst_bench_QUuid::initTestCase()
RESULT   : tst_bench_QUuid::qRandomUuid_vs_createUuid():"qRandomUuid()":
     97.821250 CPU ticks per iteration (total: 19,564,250, iterations: 200000)
RESULT   : tst_bench_QUuid::qRandomUuid_vs_createUuid():"QUuid::createUuid":
     108.41198 CPU ticks per iteration (total: 21,682,396, iterations: 200000)
PASS  : tst_bench_QUuid::qRandomUuid_vs_createUuid()
RESULT   : tst_bench_QUuid::createUuid():
     57.377920 CPU ticks per iteration (total: 11,475,584, iterations: 200000)
PASS  : tst_bench_QUuid::createUuid()
RESULT   : tst_bench_QUuid::fromChar():
     81.606610 CPU ticks per iteration (total: 16,321,322, iterations: 200000)
PASS  : tst_bench_QUuid::fromChar()
RESULT   : tst_bench_QUuid::toString():
     79.527925 CPU ticks per iteration (total: 15,905,585, iterations: 200000)
PASS  : tst_bench_QUuid::toString()
RESULT   : tst_bench_QUuid::fromString():
     78.037890 CPU ticks per iteration (total: 15,607,578, iterations: 200000)
PASS  : tst_bench_QUuid::fromString()
RESULT   : tst_bench_QUuid::toByteArray():
     78.505810 CPU ticks per iteration (total: 15,701,162, iterations: 200000)
PASS  : tst_bench_QUuid::toByteArray()
RESULT   : tst_bench_QUuid::fromByteArray():
     79.680680 CPU ticks per iteration (total: 15,936,136, iterations: 200000)
PASS  : tst_bench_QUuid::fromByteArray()
RESULT   : tst_bench_QUuid::toRfc4122():
     62.749495 CPU ticks per iteration (total: 12,549,899, iterations: 200000)
PASS  : tst_bench_QUuid::toRfc4122()
RESULT   : tst_bench_QUuid::fromRfc4122():
     7.604070 CPU ticks per iteration (total: 1,520,814, iterations: 200000)
PASS  : tst_bench_QUuid::fromRfc4122()
RESULT   : tst_bench_QUuid::toDataStream():
     100.19905 CPU ticks per iteration (total: 20,039,811, iterations: 200000)
PASS  : tst_bench_QUuid::toDataStream()
RESULT   : tst_bench_QUuid::fromDataStream():
     68.303560 CPU ticks per iteration (total: 13,660,712, iterations: 200000)
PASS  : tst_bench_QUuid::fromDataStream()
RESULT   : tst_bench_QUuid::isNull():
     6.075315 CPU ticks per iteration (total: 1,215,063, iterations: 200000)
PASS  : tst_bench_QUuid::isNull()
RESULT   : tst_bench_QUuid::operatorLess():
     18.49353 CPU ticks per iteration (total: 3,698,706, iterations: 200000)
PASS  : tst_bench_QUuid::operatorLess()
RESULT   : tst_bench_QUuid::operatorMore():
     18.51902 CPU ticks per iteration (total: 3,703,804, iterations: 200000)
PASS  : tst_bench_QUuid::operatorMore()
PASS  : tst_bench_QUuid::cleanupTestCase()
Totals: 16 passed, 0 failed, 0 skipped
********* Finished testing of tst_bench_QUuid *********

Signed-off-by: Ivailo Monev <xakepa10@gmail.com>

src/core/tools/qbytearray.cpp

@@ -292,6 +292,56 @@ quint16 qChecksum(const char *data, uint len)
     return ~crc & 0xffff;
 }
 
+/*!
+    \relates QByteArray
+
+    Returns pseudo-randomly generated UUID in DCE variant as
+    described in \l{https://www.ietf.org/rfc/rfc4122.txt}.
+*/
+QByteArray qRandomUuid()
+{
+    static const ushort randiterratio = (sizeof(int) / sizeof(uchar));
+    Q_ASSERT(randiterratio > 1);
+    QSTACKARRAY(uchar, randombuf, 16);
+    uchar *randombufiter = randombuf;
+    for (ushort i = 0; i < (16 / randiterratio); i++) {
+        *randombufiter = qrand();
+        randombufiter += randiterratio;
+    }
+    randombuf[6] = (randombuf[6] & 0x0FFF) | 0x4000; // random version
+    randombuf[8] = (randombuf[8] & 0x3F) | 0x80; // DCE variant
+
+#define UUID_TOHEX(bufi, randi) \
+    uuidbuf[bufi] = tohex[(randombuf[randi] >> 4) & 0xf]; \
+    uuidbuf[bufi + 1] = tohex[randombuf[randi] & 0xf];
+
+    static const char tohex[] = "0123456789abcdef";
+    QSTACKARRAY(char, uuidbuf, 37);
+    UUID_TOHEX(0, 0);
+    UUID_TOHEX(2, 1);
+    UUID_TOHEX(4, 2);
+    UUID_TOHEX(6, 3);
+    uuidbuf[8] = '-';
+    UUID_TOHEX(9, 4);
+    UUID_TOHEX(11, 5);
+    uuidbuf[13] = '-';
+    UUID_TOHEX(14, 6);
+    UUID_TOHEX(16, 7);
+    uuidbuf[18] = '-';
+    UUID_TOHEX(19, 8);
+    UUID_TOHEX(21, 9);
+    uuidbuf[23] = '-';
+    UUID_TOHEX(24, 10);
+    UUID_TOHEX(26, 11);
+    UUID_TOHEX(28, 12);
+    UUID_TOHEX(30, 13);
+    UUID_TOHEX(32, 14);
+    UUID_TOHEX(34, 15);
+
+#undef UUID_TOHEX
+
+    return QByteArray(reinterpret_cast<char*>(uuidbuf), sizeof(uuidbuf));
+}
 #ifndef QT_NO_COMPRESS
 /*!
     \fn QByteArray qCompress(const QByteArray& data, int compressionLevel)

src/core/tools/qbytearray.h

@@ -71,6 +71,8 @@ inline int qstrnicmp(const char *str1, const char *str2, uint len)
 // qChecksum: Internet checksum
 Q_CORE_EXPORT quint16 qChecksum(const char *s, uint len);
 
+Q_CORE_EXPORT QByteArray qRandomUuid();
+
 class QByteRef;
 class QString;
 class QDataStream;

tests/benchmarks/core/plugin/quuid/tst_quuid.cpp

@@ -34,6 +34,8 @@ public:
     { }
 
 private slots:
+    void qRandomUuid_vs_createUuid_data();
+    void qRandomUuid_vs_createUuid();
     void createUuid();
     void fromChar();
     void toString();
@@ -49,6 +51,29 @@ private slots:
     void operatorMore();
 };
 
+void tst_bench_QUuid::qRandomUuid_vs_createUuid_data()
+{
+    QTest::addColumn<bool>("qrandomuuid");
+
+    QTest::newRow("qRandomUuid()") << true;
+    QTest::newRow("QUuid::createUuid") << false;
+}
+
+void tst_bench_QUuid::qRandomUuid_vs_createUuid()
+{
+    QFETCH(bool, qrandomuuid);
+
+    if (qrandomuuid) {
+        QBENCHMARK {
+            (void)qRandomUuid();
+        }
+    } else {
+        QBENCHMARK {
+            (void)QUuid::createUuid().toByteArray();
+        }
+    }
+}
+
 void tst_bench_QUuid::createUuid()
 {
     QBENCHMARK {