From 5f4c95aa11d9dae70ffee4897dfe6d5de839f87c Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Tue, 18 Aug 2020 07:19:55 +1000
Subject: [PATCH] rand/xoshiro: add a std::seed_seq constructor

---
 rand/xoshiro.cpp | 18 ++++++++++++++++++
 rand/xoshiro.hpp |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/rand/xoshiro.cpp b/rand/xoshiro.cpp
index de35a65f..204324d7 100644
--- a/rand/xoshiro.cpp
+++ b/rand/xoshiro.cpp
@@ -36,6 +36,24 @@ xoshiro256plusplus::xoshiro256plusplus (u64 _seed)
 }
 
 
+//-----------------------------------------------------------------------------
+xoshiro256plusplus::xoshiro256plusplus (std::seed_seq &seq)
+{
+    std::generate (
+        std::begin (m_state),
+        std::end   (m_state),
+        [&] (void) {
+            u64 parts[2];
+            seq.generate (
+                std::begin (parts),
+                std::end   (parts)
+            );
+            return parts[0] << 4 | parts[1];
+        }
+    );
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 u64
 xoshiro256plusplus::operator() (void)
diff --git a/rand/xoshiro.hpp b/rand/xoshiro.hpp
index 1344c057..204e1548 100644
--- a/rand/xoshiro.hpp
+++ b/rand/xoshiro.hpp
@@ -20,6 +20,7 @@
 #include "../std.hpp"
 
 #include <limits>
+#include <random>
 
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -29,6 +30,7 @@ namespace cruft::rand {
         using result_type = u64;
 
         xoshiro256plusplus (u64 seed);
+        xoshiro256plusplus (std::seed_seq&);
 
         static constexpr result_type min (void)
         {