From 497c6efc5555f3c45b7e092b461f39a3d89de865 Mon Sep 17 00:00:00 2001
From: Kae <80987908+Novaenia@users.noreply.github.com>
Date: Fri, 2 Aug 2024 11:53:59 +1000
Subject: [PATCH] Fix RNG bugs from upgrade to C++17

staticRandomShuffle now uses its own tiny impl of the deprecated std::random_shuffle, producing identical results in testing
---
 source/core/StarRandom.hpp       |  4 ++--
 source/core/StarStaticRandom.hpp | 13 ++++++++-----
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/source/core/StarRandom.hpp b/source/core/StarRandom.hpp
index a67a2c5..6afb2ad 100644
--- a/source/core/StarRandom.hpp
+++ b/source/core/StarRandom.hpp
@@ -208,8 +208,8 @@ typename Container::value_type Random::randValueFrom(
 
 template <typename Container>
 void Random::shuffle(Container& container) {
-  size_t max = container.size();
-  std::shuffle(container.begin(), container.end(), URBG<size_t>([max]() { return Random::randUInt(max - 1); }));
+  RandomSource random;
+  std::shuffle(container.begin(), container.end(), URBG<size_t>([&]() { return static_cast<size_t>(random.randu64()); }));
 }
 
 }
diff --git a/source/core/StarStaticRandom.hpp b/source/core/StarStaticRandom.hpp
index 1b355c4..d95463e 100644
--- a/source/core/StarStaticRandom.hpp
+++ b/source/core/StarStaticRandom.hpp
@@ -134,11 +134,14 @@ private:
 
 template <typename Container, typename T, typename... TL>
 void staticRandomShuffle(Container& container, T const& d, TL const&... rest) {
-  int mix = 0;
-  size_t max = container.size();
-  std::shuffle(container.begin(), container.end(), URBG<size_t>([&]() {
-    return staticRandomU32Range(0, max - 1, ++mix, d, rest...);
-  }));
+  auto begin = container.begin();
+  auto end = container.end();
+  auto it = begin;
+  for (int i = 1, mix = 0; ++it != end; ++i) {
+    int off = staticRandomU32Range(0, i, ++mix, d, rest...);
+    if (off != i)
+      std::swap(*it, *(begin + off));    
+  }
 }
 
 }