[29] | 1 | |
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| 2 | /* |
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| 3 | * |
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| 4 | * (C) Copyright John Maddock 1999-2005. |
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| 5 | * Use, modification and distribution are subject to the |
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| 6 | * Boost Software License, Version 1.0. (See accompanying file |
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| 7 | * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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| 8 | * |
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| 9 | * This file provides some example of type_traits usage - |
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| 10 | * by "optimising" various algorithms: |
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| 11 | * |
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| 12 | * opt::fill - optimised for trivial copy/small types (cf std::fill) |
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| 13 | * |
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| 14 | */ |
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| 15 | |
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| 16 | #include <iostream> |
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| 17 | #include <typeinfo> |
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| 18 | #include <algorithm> |
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| 19 | #include <iterator> |
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| 20 | #include <memory> |
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| 21 | #include <cstring> |
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| 22 | |
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| 23 | #include <boost/test/included/prg_exec_monitor.hpp> |
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| 24 | #include <boost/timer.hpp> |
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| 25 | #include <boost/type_traits.hpp> |
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| 26 | |
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| 27 | #if defined(BOOST_NO_STDC_NAMESPACE) || (defined(std) && defined(__SGI_STL_PORT)) |
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| 28 | namespace std{ using :: memset; } |
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| 29 | #endif |
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| 30 | |
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| 31 | using std::cout; |
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| 32 | using std::endl; |
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| 33 | using std::cin; |
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| 34 | |
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| 35 | namespace opt{ |
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| 36 | // |
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| 37 | // fill |
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| 38 | // same as std::fill, but uses memset where appropriate |
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| 39 | // |
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| 40 | namespace detail{ |
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| 41 | |
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| 42 | template <typename I, typename T, bool b> |
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| 43 | void do_fill(I first, I last, const T& val, const boost::integral_constant<bool, b>&) |
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| 44 | { |
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| 45 | while(first != last) |
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| 46 | { |
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| 47 | *first = val; |
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| 48 | ++first; |
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| 49 | } |
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| 50 | } |
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| 51 | |
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| 52 | template <typename T> |
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| 53 | void do_fill(T* first, T* last, const T& val, const boost::true_type&) |
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| 54 | { |
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| 55 | std::memset(first, val, last-first); |
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| 56 | } |
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| 57 | |
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| 58 | } |
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| 59 | |
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| 60 | template <class I, class T> |
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| 61 | inline void fill(I first, I last, const T& val) |
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| 62 | { |
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| 63 | // |
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| 64 | // We can do an optimised fill if T has a trivial assignment |
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| 65 | // operator and if it's size is one: |
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| 66 | // |
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| 67 | typedef boost::integral_constant<bool, |
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| 68 | ::boost::has_trivial_assign<T>::value && (sizeof(T) == 1)> truth_type; |
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| 69 | detail::do_fill(first, last, val, truth_type()); |
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| 70 | } |
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| 71 | |
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| 72 | }; // namespace opt |
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| 73 | |
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| 74 | // |
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| 75 | // define some global data: |
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| 76 | // |
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| 77 | const int array_size = 1000; |
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| 78 | int i_array_[array_size] = {0,}; |
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| 79 | const int ci_array_[array_size] = {0,}; |
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| 80 | char c_array_[array_size] = {0,}; |
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| 81 | const char cc_array_[array_size] = { 0,}; |
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| 82 | // |
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| 83 | // since arrays aren't iterators we define a set of pointer |
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| 84 | // aliases into the arrays (otherwise the compiler is entitled |
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| 85 | // to deduce the type passed to the template functions as |
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| 86 | // T (&)[N] rather than T*). |
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| 87 | int* i_array = i_array_; |
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| 88 | const int* ci_array = ci_array_; |
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| 89 | char* c_array = c_array_; |
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| 90 | const char* cc_array = cc_array_; |
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| 91 | |
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| 92 | const int iter_count = 1000000; |
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| 93 | |
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| 94 | int cpp_main(int argc, char* argv[]) |
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| 95 | { |
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| 96 | boost::timer t; |
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| 97 | double result; |
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| 98 | int i; |
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| 99 | // |
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| 100 | // test destroy_array, |
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| 101 | // compare destruction time of an array of ints |
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| 102 | // with unoptimised form. |
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| 103 | // |
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| 104 | cout << "Measuring times in micro-seconds per 1000 elements processed" << endl << endl; |
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| 105 | |
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| 106 | cout << "testing fill(char)...\n" |
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| 107 | "[Some standard library versions may already perform this optimisation.]" << endl; |
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| 108 | |
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| 109 | // cache load: |
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| 110 | opt::fill(c_array, c_array + array_size, (char)3); |
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| 111 | |
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| 112 | // time optimised version: |
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| 113 | t.restart(); |
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| 114 | for(i = 0; i < iter_count; ++i) |
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| 115 | { |
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| 116 | opt::fill(c_array, c_array + array_size, (char)3); |
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| 117 | } |
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| 118 | result = t.elapsed(); |
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| 119 | cout << "opt::fill<char*, char>: " << result << endl; |
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| 120 | |
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| 121 | // cache load: |
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| 122 | std::fill(c_array, c_array + array_size, (char)3); |
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| 123 | |
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| 124 | // time standard version: |
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| 125 | t.restart(); |
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| 126 | for(i = 0; i < iter_count; ++i) |
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| 127 | { |
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| 128 | std::fill(c_array, c_array + array_size, (char)3); |
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| 129 | } |
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| 130 | result = t.elapsed(); |
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| 131 | cout << "std::fill<char*, char>: " << result << endl << endl; |
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| 132 | |
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| 133 | cout << "testing fill(int)...\n" << endl; |
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| 134 | |
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| 135 | // cache load: |
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| 136 | opt::fill(i_array, i_array + array_size, 3); |
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| 137 | |
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| 138 | // timer optimised version: |
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| 139 | t.restart(); |
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| 140 | for(i = 0; i < iter_count; ++i) |
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| 141 | { |
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| 142 | opt::fill(i_array, i_array + array_size, 3); |
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| 143 | } |
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| 144 | result = t.elapsed(); |
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| 145 | cout << "opt::fill<int*, int>: " << result << endl; |
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| 146 | |
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| 147 | // cache load: |
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| 148 | std::fill(i_array, i_array + array_size, 3); |
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| 149 | |
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| 150 | // time standard version: |
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| 151 | t.restart(); |
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| 152 | for(i = 0; i < iter_count; ++i) |
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| 153 | { |
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| 154 | std::fill(i_array, i_array + array_size, 3); |
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| 155 | } |
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| 156 | result = t.elapsed(); |
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| 157 | cout << "std::fill<int*, int>: " << result << endl << endl; |
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| 158 | |
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| 159 | return 0; |
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| 160 | } |
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| 161 | |
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| 162 | |
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| 163 | |
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| 164 | |
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| 165 | |
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| 166 | |
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