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ReinterpretCtr.hpp
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32 #ifndef __ReinterpretCtr_dot_hpp__
33 #define __ReinterpretCtr_dot_hpp__
34 
36 #include <cstring>
37 
38 namespace r123{
53 template <typename ToType, typename CBRNG>
55  typedef ToType ctr_type;
56  typedef typename CBRNG::key_type key_type;
57  typedef typename CBRNG::ctr_type bctype;
58  typedef typename CBRNG::ukey_type ukey_type;
59  R123_STATIC_ASSERT(sizeof(ToType) == sizeof(bctype) && sizeof(typename bctype::value_type) != 16,
60  "ReinterpretCtr: sizeof(ToType) is not the same as sizeof(CBRNG::ctr_type) or CBRNG::ctr_type::value_type looks like it might be __m128i");
61  // It's amazingly difficult to safely do conversions with __m128i.
62  // If we use the operator() implementation below with a CBRNG
63  // whose ctr_type is r123array1xm128i, gcc4.6 optimizes away the
64  // memcpys, inlines the operator()(c,k), and produces assembly
65  // language that ends with an aesenclast instruction with a
66  // destination operand pointing to an unaligned memory address ...
67  // Segfault! See: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50444
68  // MSVC also produces code that crashes. We suspect a
69  // similar mechanism but haven't done the debugging necessary to
70  // be sure. We were able to 'fix' gcc4.6 by making bc a mutable
71  // data member rather than declaring it in the scope of
72  // operator(). That didn't fix the MSVC problems, though.
73  //
74  // Conclusion - don't touch __m128i, at least for now. The
75  // easiest (but highly imprecise) way to do that is the static
76  // assertion above that rejects bctype::value_types of size 16. -
77  // Sep 2011.
79  bctype bc;
80  std::memcpy(&bc, &c, sizeof(c));
81  CBRNG b;
82  bc = b(bc, k);
83  std::memcpy(&c, &bc, sizeof(bc));
84  return c;
85  }
86 };
87 } // namespace r123
88 #endif
Definition: ReinterpretCtr.hpp:54
CBRNG::ukey_type ukey_type
Definition: ReinterpretCtr.hpp:58
ctr_type operator()(ctr_type c, key_type k)
Definition: ReinterpretCtr.hpp:78
CBRNG::ctr_type bctype
Definition: ReinterpretCtr.hpp:57
CBRNG::key_type key_type
Definition: ReinterpretCtr.hpp:56
ToType ctr_type
Definition: ReinterpretCtr.hpp:55