From 02bac59cb8c83b367d8ae659513c437f4f56b8c9 Mon Sep 17 00:00:00 2001
From: SupSuper <supsuper@gmail.com>
Date: Wed, 14 Oct 2020 12:15:26 +0100
Subject: [PATCH] Make shuffle deterministic

---
 src/Engine/RNG.cpp | 11 -----------
 src/Engine/RNG.h   | 10 ++++++----
 2 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/src/Engine/RNG.cpp b/src/Engine/RNG.cpp
index c0dd7db7bc..e74614b2c6 100644
--- a/src/Engine/RNG.cpp
+++ b/src/Engine/RNG.cpp
@@ -152,17 +152,6 @@ bool percent(int value)
 	return (generate(0, 99) < value);
 }
 
-/**
- * Generates a random positive integer up to a number.
- * @param max Maximum number, exclusive.
- * @return Generated number.
- */
-int generateEx(int max)
-{
-	uint64_t num = next();
-	return (int)(num % max);
-}
-
 }
 
 }
diff --git a/src/Engine/RNG.h b/src/Engine/RNG.h
index b9af0783e6..349b4e760c 100644
--- a/src/Engine/RNG.h
+++ b/src/Engine/RNG.h
@@ -18,6 +18,7 @@
  * along with OpenXcom.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <algorithm>
+#include <vector>
 #define __STDC_LIMIT_MACROS
 #include <stdint.h>
 
@@ -45,17 +46,18 @@ namespace RNG
 	double boxMuller(double m = 0, double s = 1);
 	/// Generates a percentage chance.
 	bool percent(int value);
-	/// Generates a random integer number, exclusive.
-	int generateEx(int max);
 	/// Shuffles a list randomly.
 	/**
 	 * Randomly changes the orders of the elements in a list.
 	 * @param list The container to randomize.
 	 */
 	template <typename T>
-	void shuffle(T &list)
+	void shuffle(std::vector<T> &list)
 	{
-		std::random_shuffle(list.begin(), list.end(), generateEx);
+		if (list.empty())
+			return;
+		for (size_t i = list.size() - 1; i > 0; --i)
+			std::swap(list[i], list[generate(0, i)]);
 	}
 }