From 259c3de4178975791b8d4df66723b1e01cce8c7f Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Sat, 15 Dec 2018 15:36:51 +1100
Subject: [PATCH] bitwise: add 'bitfield' type suitable for unions

---
 bitwise.hpp | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/bitwise.hpp b/bitwise.hpp
index 3b1d098f..4f4de06b 100644
--- a/bitwise.hpp
+++ b/bitwise.hpp
@@ -126,6 +126,37 @@ namespace cruft {
 
         return (val >> lo) & (ones >> (sizeof (ValueT) * 8 - (hi - lo + 1)));
     }
-}
+
+
+    template <
+        typename ValueT,
+        size_t OffsetV,
+        size_t SizeV
+    >
+    class bitfield {
+    public:
+        static_assert (SizeV > 0);
+        static_assert (OffsetV + SizeV <= sizeof (ValueT) * 8);
+
+        decltype(auto) operator+ () const { return +value; }
+
+        operator auto() const
+        {
+            auto const MASK = (1u << SizeV) - 1u;
+            auto const SHIFT = sizeof (ValueT) * 8 - OffsetV - SizeV;
+
+            return (value >> SHIFT) & MASK;
+        }
+
+        ValueT value;
+    };
+
+
+    template <typename ValueT, size_t Offset, size_t Size>
+    std::ostream& operator<< (std::ostream &os, bitfield<ValueT,Offset,Size> const &val)
+    {
+        return os << +ValueT(val);
+    }
+};
 
 #endif