ReinterpretCtr.hpp

/*
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#ifndef __ReinterpretCtr_dot_hpp__
#define __ReinterpretCtr_dot_hpp__

#include "features/compilerfeatures.h"
#include <cstring>

namespace random_iterator_r123 {
  template <typename ToType, typename CBRNG>
  struct ReinterpretCtr {
    typedef ToType ctr_type;
    typedef typename CBRNG::key_type key_type;
    typedef typename CBRNG::ctr_type bctype;
    typedef typename CBRNG::ukey_type ukey_type;
    RANDOM_ITERATOR_R123_STATIC_ASSERT(
        sizeof(ToType) == sizeof(bctype) && sizeof(typename bctype::value_type) != 16,
        "ReinterpretCtr:  sizeof(ToType) is not the same as sizeof(CBRNG::ctr_type) or "
        "CBRNG::ctr_type::value_type looks like it might be __m128i");
    // It's amazingly difficult to safely do conversions with __m128i.
    // If we use the operator() implementation below with a CBRNG
    // whose ctr_type is r123array1xm128i, gcc4.6 optimizes away the
    // memcpys, inlines the operator()(c,k), and produces assembly
    // language that ends with an aesenclast instruction with a
    // destination operand pointing to an unaligned memory address ...
    // Segfault!  See:  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50444
    // MSVC also produces code that crashes.  We suspect a
    // similar mechanism but haven't done the debugging necessary to
    // be sure.  We were able to 'fix' gcc4.6 by making bc a mutable
    // data member rather than declaring it in the scope of
    // operator().  That didn't fix the MSVC problems, though.
    //
    // Conclusion - don't touch __m128i, at least for now.  The
    // easiest (but highly imprecise) way to do that is the static
    // assertion above that rejects bctype::value_types of size 16. -
    // Sep 2011.
    ctr_type operator()(ctr_type c, key_type k) {
      bctype bc;
      std::memcpy(&bc, &c, sizeof(c));
      CBRNG b;
      bc = b(bc, k);
      std::memcpy(&c, &bc, sizeof(bc));
      return c;
    }
  };
} // namespace random_iterator_r123
#endif