[857] | 1 | /* boost random/detail/signed_unsigned_compare.hpp header file
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| 2 | *
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| 3 | * Copyright Jens Maurer 2000-2001
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| 4 | * Distributed under the Boost Software License, Version 1.0. (See
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| 5 | * accompanying file LICENSE_1_0.txt or copy at
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| 6 | * http://www.boost.org/LICENSE_1_0.txt)
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| 7 | *
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| 8 | * See http://www.boost.org for most recent version including documentation.
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| 9 | *
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| 10 | * Revision history
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| 11 | */
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| 12 |
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| 13 |
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| 14 | #ifndef BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE
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| 15 | #define BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE
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| 16 |
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| 17 | #include <boost/limits.hpp>
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| 18 |
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| 19 | namespace boost {
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| 20 | namespace random {
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| 21 |
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| 22 | /*
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| 23 | * Correctly compare two numbers whose types possibly differ in signedness.
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| 24 | * See boost::numeric_cast<> for the general idea.
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| 25 | * Most "if" statements involve only compile-time constants, so the
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| 26 | * optimizing compiler can do its job easily.
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| 27 | *
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| 28 | * With most compilers, the straightforward implementation produces a
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| 29 | * bunch of (legitimate) warnings. Some template magic helps, though.
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| 30 | */
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| 31 |
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| 32 | namespace detail {
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| 33 | template<bool signed1, bool signed2>
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| 34 | struct do_compare
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| 35 | { };
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| 36 |
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| 37 | template<>
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| 38 | struct do_compare<false, false>
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| 39 | {
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| 40 | // cast to the larger type is automatic with built-in types
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| 41 | template<class T1, class T2>
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| 42 | static bool equal(T1 x, T2 y) { return x == y; }
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| 43 | template<class T1, class T2>
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| 44 | static bool lessthan(T1 x, T2 y) { return x < y; }
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| 45 | };
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| 46 |
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| 47 | template<>
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| 48 | struct do_compare<true, true> : do_compare<false, false>
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| 49 | { };
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| 50 |
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| 51 | template<>
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| 52 | struct do_compare<true, false>
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| 53 | {
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| 54 | template<class T1, class T2>
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| 55 | static bool equal(T1 x, T2 y) { return x >= 0 && static_cast<T2>(x) == y; }
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| 56 | template<class T1, class T2>
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| 57 | static bool lessthan(T1 x, T2 y) { return x < 0 || static_cast<T2>(x) < y; }
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| 58 | };
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| 59 |
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| 60 | template<>
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| 61 | struct do_compare<false, true>
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| 62 | {
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| 63 | template<class T1, class T2>
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| 64 | static bool equal(T1 x, T2 y) { return y >= 0 && x == static_cast<T1>(y); }
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| 65 | template<class T1, class T2>
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| 66 | static bool lessthan(T1 x, T2 y) { return y >= 0 && x < static_cast<T1>(y); }
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| 67 | };
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| 68 |
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| 69 | } // namespace detail
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| 70 |
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| 71 |
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| 72 | template<class T1, class T2>
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| 73 | int equal_signed_unsigned(T1 x, T2 y)
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| 74 | {
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| 75 | typedef std::numeric_limits<T1> x_traits;
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| 76 | typedef std::numeric_limits<T2> y_traits;
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| 77 | return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::equal(x, y);
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| 78 | }
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| 79 |
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| 80 | template<class T1, class T2>
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| 81 | int lessthan_signed_unsigned(T1 x, T2 y)
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| 82 | {
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| 83 | typedef std::numeric_limits<T1> x_traits;
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| 84 | typedef std::numeric_limits<T2> y_traits;
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| 85 | return detail::do_compare<x_traits::is_signed, y_traits::is_signed>::lessthan(x, y);
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| 86 | }
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| 87 |
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| 88 | } // namespace random
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| 89 | } // namespace boost
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| 90 |
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| 91 | #endif // BOOST_RANDOM_DETAIL_SIGNED_UNSIGNED_COMPARE
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