From cf268a1960685e099a0de137c20a486afa9e1490 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Sun, 3 Feb 2019 13:52:56 +1100
Subject: [PATCH] bitwise: offset should start from least significant bits

---
 bitwise.hpp | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/bitwise.hpp b/bitwise.hpp
index 596242c2..e6d9b3b0 100644
--- a/bitwise.hpp
+++ b/bitwise.hpp
@@ -140,7 +140,7 @@ namespace cruft {
     ///
     /// \tparam ValueT   the underlying integral type
     /// \tparam OffsetV  the index of the first bit of the range (where 0 is
-    ///                  most significant)
+    ///                  least significant)
     /// \tparam SizeV    the number of bits in the range. Must be strictly
     ///                  positive.
     template <
@@ -148,11 +148,10 @@ namespace cruft {
         size_t OffsetV,
         size_t SizeV
     >
-    class bitfield {
+    class [[gnu::packed]] bitfield {
     public:
         static_assert (SizeV > 0);
         static_assert (OffsetV + SizeV <= sizeof (ValueT) * 8);
-        static_assert (sizeof (ValueT) == sizeof (bitfield));
 
         decltype(auto)
         operator+ () const { return +value; }
@@ -160,9 +159,7 @@ namespace cruft {
         operator auto() const
         {
             auto const MASK = (1u << SizeV) - 1u;
-            auto const SHIFT = sizeof (ValueT) * 8 - OffsetV - SizeV;
-
-            return (value >> SHIFT) & MASK;
+            return (value >> OffsetV) & MASK;
         }
 
         ValueT value;