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# Random123/ReinterpretCtr.hpp

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    00001 /*
    00002 Copyright 2010-2011, D. E. Shaw Research.
    00003 All rights reserved.
    00004
    00005 Redistribution and use in source and binary forms, with or without
    00006 modification, are permitted provided that the following conditions are
    00007 met:
    00008
    00009 * Redistributions of source code must retain the above copyright
    00010   notice, this list of conditions, and the following disclaimer.
    00011
    00012 * Redistributions in binary form must reproduce the above copyright
    00013   notice, this list of conditions, and the following disclaimer in the
    00014   documentation and/or other materials provided with the distribution.
    00015
    00016 * Neither the name of D. E. Shaw Research nor the names of its
    00017   contributors may be used to endorse or promote products derived from
    00018   this software without specific prior written permission.
    00019
    00020 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    00021 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    00022 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    00023 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    00024 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    00025 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    00026 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    00027 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    00028 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    00029 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    00030 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
    00031 */
    00032 #ifndef __ReinterpretCtr_dot_hpp__
    00033 #define __ReinterpretCtr_dot_hpp__
    00034
    00035 #include "features/compilerfeatures.h"
    00036 #include <cstring>
    00037
    00038 namespace r123{
    00053 template <typename ToType, typename CBRNG>
    00054 struct ReinterpretCtr{
    00055     typedef ToType ctr_type;
    00056     typedef typename CBRNG::key_type key_type;
    00057     typedef typename CBRNG::ctr_type bctype;
    00058     typedef typename CBRNG::ukey_type ukey_type;
    00059     R123_STATIC_ASSERT(sizeof(ToType) == sizeof(bctype) && sizeof(typename bctype::value_type) != 16,
    00060                        "ReinterpretCtr:  sizeof(ToType) is not the same as sizeof(CBRNG::ctr_type) or CBRNG::ctr_type::value_type looks like it might be __m128i");
    00061     // It's amazingly difficult to safely do conversions with __m128i.
    00062     // If we use the operator() implementation below with a CBRNG
    00063     // whose ctr_type is r123array1xm128i, gcc4.6 optimizes away the
    00064     // memcpys, inlines the operator()(c,k), and produces assembly
    00065     // language that ends with an aesenclast instruction with a
    00066     // destination operand pointing to an unaligned memory address ...
    00067     // Segfault!  See:  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50444
    00068     // MSVC also produces code that crashes.  We suspect a
    00069     // similar mechanism but haven't done the debugging necessary to
    00070     // be sure.  We were able to 'fix' gcc4.6 by making bc a mutable
    00071     // data member rather than declaring it in the scope of
    00072     // operator().  That didn't fix the MSVC problems, though.
    00073     //
    00074     // Conclusion - don't touch __m128i, at least for now.  The
    00075     // easiest (but highly imprecise) way to do that is the static
    00076     // assertion above that rejects bctype::value_types of size 16. -
    00077     // Sep 2011.
    00078     ctr_type  operator()(ctr_type c, key_type k){
    00079         bctype bc;
    00080         std::memcpy(&bc, &c, sizeof(c));
    00081         CBRNG b;
    00082         bc = b(bc, k);
    00083         std::memcpy(&c, &bc, sizeof(bc));
    00084         return c;
    00085     }
    00086 };
    00087 } // namespace r123
    00088 #endif

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