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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