From 3c7a6a7a581f9ea6f05a22a912d660c5402a1fa8 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Sat, 21 Oct 2017 11:24:54 -0700
Subject: QRandomGenerator: Enforce the use of 32-bit integers in the engine

std::mt19937 is defined as operating on uint_fast32_t, which is usually
just a 32-bit integer. That's not the case on 64-bit Linux, where it is
actually 64-bit wide, meaning sizeof(std::mt19937) jumps from 2504 to
5000 bytes, with exactly 50% of it filled with zeroes. The seed()
function also needs a large zero-extending loop.

Change-Id: Icaa86fc7b54d4b368c0efffd14efa911e2a40b44
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/global/qrandom.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/corelib')

diff --git a/src/corelib/global/qrandom.h b/src/corelib/global/qrandom.h
index bde64646a4..005de0941f 100644
--- a/src/corelib/global/qrandom.h
+++ b/src/corelib/global/qrandom.h
@@ -177,7 +177,8 @@ private:
     friend class QRandomGenerator64;
     struct SystemGenerator;
     struct SystemAndGlobalGenerators;
-    typedef std::mt19937 RandomEngine;
+    using RandomEngine = std::mersenne_twister_engine<quint32,
+        32,624,397,31,0x9908b0df,11,0xffffffff,7,0x9d2c5680,15,0xefc60000,18,1812433253>;
 
     union Storage {
         uint dummy;
-- 
cgit v1.2.3