49 lines
1.2 KiB
C++
49 lines
1.2 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2019 Danny Robson <danny@nerdcruft.net>
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*/
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#include "rdrand.hpp"
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using cruft::rand::rdrand;
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///////////////////////////////////////////////////////////////////////////////
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rdrand::rdrand ()
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{ ; }
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//---------------------------------------------------------------------------------------
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rdrand::rdrand (std::string const &)
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: rdrand ()
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{ ; }
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///////////////////////////////////////////////////////////////////////////////
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rdrand::result_type
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rdrand::operator() ()
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{
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uint64_t res;
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char success;
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__asm__ __volatile__ (
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"rdrand %0;"
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"setc %1;"
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: "=r" (res)
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, "=qm" (success)
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);
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if (!__builtin_expect(success, 1))
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throw std::runtime_error ("no value available for rdrand");
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// As long as the u64 we just grabbed is of a type we can truncate then
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// we'll do just that and return it.
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static_assert (sizeof (result_type) <= sizeof (res));
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static_assert (std::is_signed_v<result_type> == std::is_signed_v<decltype(res)>);
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return static_cast<result_type> (res);
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}
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