1 | // Copyright Alexander Nasonov & Paul A. Bristow 2006. |
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2 | |
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3 | // Use, modification and distribution are subject to the |
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4 | // Boost Software License, Version 1.0. |
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5 | // (See accompanying file LICENSE_1_0.txt |
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6 | // or copy at http://www.boost.org/LICENSE_1_0.txt) |
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7 | |
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8 | #ifndef BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED |
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9 | #define BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED |
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10 | |
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11 | #include <climits> |
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12 | #include <ios> |
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13 | #include <limits> |
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14 | |
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15 | #include <boost/config.hpp> |
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16 | #include <boost/integer_traits.hpp> |
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17 | |
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18 | #ifndef BOOST_NO_IS_ABSTRACT |
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19 | // Fix for SF:1358600 - lexical_cast & pure virtual functions & VC 8 STL |
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20 | #include <boost/mpl/if.hpp> |
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21 | #include <boost/type_traits/is_abstract.hpp> |
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22 | #endif |
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23 | |
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24 | #if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || \ |
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25 | (defined(BOOST_MSVC) && (BOOST_MSVC<1310)) |
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26 | |
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27 | #define BOOST_LCAST_NO_COMPILE_TIME_PRECISION |
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28 | #endif |
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29 | |
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30 | #ifdef BOOST_LCAST_NO_COMPILE_TIME_PRECISION |
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31 | #include <boost/assert.hpp> |
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32 | #else |
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33 | #include <boost/static_assert.hpp> |
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34 | #endif |
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35 | |
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36 | namespace boost { namespace detail { |
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37 | |
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38 | class lcast_abstract_stub {}; |
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39 | |
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40 | #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION |
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41 | // Calculate an argument to pass to std::ios_base::precision from |
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42 | // lexical_cast. See alternative implementation for broken standard |
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43 | // libraries in lcast_get_precision below. Keep them in sync, please. |
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44 | template<class T> |
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45 | struct lcast_precision |
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46 | { |
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47 | #ifdef BOOST_NO_IS_ABSTRACT |
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48 | typedef std::numeric_limits<T> limits; // No fix for SF:1358600. |
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49 | #else |
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50 | typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_< |
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51 | boost::is_abstract<T> |
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52 | , std::numeric_limits<lcast_abstract_stub> |
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53 | , std::numeric_limits<T> |
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54 | >::type limits; |
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55 | #endif |
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56 | |
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57 | BOOST_STATIC_CONSTANT(bool, use_default_precision = |
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58 | !limits::is_specialized || limits::is_exact |
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59 | ); |
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60 | |
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61 | BOOST_STATIC_CONSTANT(bool, is_specialized_bin = |
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62 | !use_default_precision && |
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63 | limits::radix == 2 && limits::digits > 0 |
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64 | ); |
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65 | |
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66 | BOOST_STATIC_CONSTANT(bool, is_specialized_dec = |
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67 | !use_default_precision && |
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68 | limits::radix == 10 && limits::digits10 > 0 |
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69 | ); |
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70 | |
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71 | BOOST_STATIC_CONSTANT(std::streamsize, streamsize_max = |
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72 | boost::integer_traits<std::streamsize>::const_max |
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73 | ); |
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74 | |
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75 | BOOST_STATIC_CONSTANT(unsigned int, precision_dec = limits::digits10 + 1U); |
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76 | |
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77 | BOOST_STATIC_ASSERT(!is_specialized_dec || |
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78 | precision_dec <= streamsize_max + 0UL |
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79 | ); |
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80 | |
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81 | BOOST_STATIC_CONSTANT(unsigned long, precision_bin = |
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82 | 2UL + limits::digits * 30103UL / 100000UL |
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83 | ); |
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84 | |
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85 | BOOST_STATIC_ASSERT(!is_specialized_bin || |
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86 | (limits::digits + 0UL < ULONG_MAX / 30103UL && |
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87 | precision_bin > limits::digits10 + 0UL && |
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88 | precision_bin <= streamsize_max + 0UL) |
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89 | ); |
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90 | |
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91 | BOOST_STATIC_CONSTANT(std::streamsize, value = |
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92 | is_specialized_bin ? precision_bin |
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93 | : is_specialized_dec ? precision_dec : 6 |
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94 | ); |
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95 | }; |
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96 | #endif |
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97 | |
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98 | template<class T> |
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99 | inline std::streamsize lcast_get_precision(T* = 0) |
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100 | { |
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101 | #ifndef BOOST_LCAST_NO_COMPILE_TIME_PRECISION |
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102 | return lcast_precision<T>::value; |
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103 | #else // Follow lcast_precision algorithm at run-time: |
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104 | |
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105 | #ifdef BOOST_NO_IS_ABSTRACT |
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106 | typedef std::numeric_limits<T> limits; // No fix for SF:1358600. |
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107 | #else |
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108 | typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_< |
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109 | boost::is_abstract<T> |
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110 | , std::numeric_limits<lcast_abstract_stub> |
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111 | , std::numeric_limits<T> |
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112 | >::type limits; |
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113 | #endif |
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114 | |
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115 | bool const use_default_precision = |
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116 | !limits::is_specialized || limits::is_exact; |
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117 | |
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118 | if(!use_default_precision) |
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119 | { // Includes all built-in floating-point types, float, double ... |
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120 | // and UDT types for which digits (significand bits) is defined (not zero) |
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121 | |
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122 | bool const is_specialized_bin = |
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123 | limits::radix == 2 && limits::digits > 0; |
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124 | bool const is_specialized_dec = |
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125 | limits::radix == 10 && limits::digits10 > 0; |
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126 | std::streamsize const streamsize_max = |
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127 | (boost::integer_traits<std::streamsize>::max)(); |
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128 | |
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129 | if(is_specialized_bin) |
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130 | { // Floating-point types with |
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131 | // limits::digits defined by the specialization. |
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132 | |
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133 | unsigned long const digits = limits::digits; |
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134 | unsigned long const precision = 2UL + digits * 30103UL / 100000UL; |
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135 | // unsigned long is selected because it is at least 32-bits |
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136 | // and thus ULONG_MAX / 30103UL is big enough for all types. |
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137 | BOOST_ASSERT( |
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138 | digits < ULONG_MAX / 30103UL && |
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139 | precision > limits::digits10 + 0UL && |
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140 | precision <= streamsize_max + 0UL |
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141 | ); |
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142 | return precision; |
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143 | } |
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144 | else if(is_specialized_dec) |
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145 | { // Decimal Floating-point type, most likely a User Defined Type |
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146 | // rather than a real floating-point hardware type. |
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147 | unsigned int const precision = limits::digits10 + 1U; |
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148 | BOOST_ASSERT(precision <= streamsize_max + 0UL); |
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149 | return precision; |
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150 | } |
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151 | } |
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152 | |
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153 | // Integral type (for which precision has no effect) |
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154 | // or type T for which limits is NOT specialized, |
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155 | // so assume stream precision remains the default 6 decimal digits. |
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156 | // Warning: if your User-defined Floating-point type T is NOT specialized, |
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157 | // then you may lose accuracy by only using 6 decimal digits. |
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158 | // To avoid this, you need to specialize T with either |
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159 | // radix == 2 and digits == the number of significand bits, |
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160 | // OR |
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161 | // radix = 10 and digits10 == the number of decimal digits. |
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162 | |
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163 | return 6; |
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164 | #endif |
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165 | } |
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166 | |
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167 | template<class T> |
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168 | inline void lcast_set_precision(std::ios_base& stream, T*) |
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169 | { |
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170 | stream.precision(lcast_get_precision<T>()); |
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171 | } |
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172 | |
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173 | template<class Source, class Target> |
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174 | inline void lcast_set_precision(std::ios_base& stream, Source*, Target*) |
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175 | { |
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176 | std::streamsize const s = lcast_get_precision(static_cast<Source*>(0)); |
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177 | std::streamsize const t = lcast_get_precision(static_cast<Target*>(0)); |
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178 | stream.precision(s > t ? s : t); |
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179 | } |
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180 | |
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181 | }} |
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182 | |
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183 | #endif // BOOST_DETAIL_LCAST_PRECISION_HPP_INCLUDED |
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184 | |
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