Long live QRandomGenerator

This class provides a reasonably-secure random number generator that
does not need seeding. That is quite unlike qrand(), which requires a
seed and is low-quality (definitely not secure).

This class is also like std::random_device, but better. It provides an
operator() like std::random_device, but unlike that, it also provides a
way to fill a buffer with random data, not just one 32-bit quantity.
It's also stateless.

Finally, it also implements std::seed_seq-like generate(). It obeys the
standard requirement of the range (32-bit) but not that of the algorithm
(if you wanted that, you'd use std::seed_seq itself). Instead,
generate() fills with pure random data.

Change-Id: Icd0e0d4b27cb4e5eb892fffd14b4e3ba9ea04da8
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index c2c9ea4e67..a718689064 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -3502,7 +3502,7 @@ Q_GLOBAL_STATIC(AndroidRandomStorage, randomTLS)
     if two threads call qsrand(1) and subsequently call qrand(), the threads will get
     the same random number sequence.
 
-    \sa qrand()
+    \sa qrand(), QRandomGenerator
 */
 void qsrand(uint seed)
 {
@@ -3553,10 +3553,12 @@ void qsrand(uint seed)
     \c <stdlib.h>), the next number in the current sequence of pseudo-random
     integers.
 
-    Use \c qsrand() to initialize the pseudo-random number generator with
-    a seed value.
+    Use \c qsrand() to initialize the pseudo-random number generator with a
+    seed value. Seeding must be performed at least once on each thread. If that
+    step is skipped, then the sequence will be pre-seeded with a constant
+    value.
 
-    \sa qsrand()
+    \sa qsrand(), QRandomGenerator
 */
 int qrand()
 {