… | |
… | |
60 | |
60 | |
61 | ecb.h makes sure that the following types are defined (in the expected way): |
61 | ecb.h makes sure that the following types are defined (in the expected way): |
62 | |
62 | |
63 | int8_t uint8_t int16_t uint16_t |
63 | int8_t uint8_t int16_t uint16_t |
64 | int32_t uint32_t int64_t uint64_t |
64 | int32_t uint32_t int64_t uint64_t |
65 | intptr_t uintptr_t ptrdiff_t |
65 | intptr_t uintptr_t |
66 | |
66 | |
67 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
67 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
68 | platform (currently C<4> or C<8>). |
68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
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69 | expressions. |
69 | |
70 | |
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71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
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72 | |
70 | =head2 LANGUAGE/COMPILER VERSIONS |
73 | =head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS |
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74 | |
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75 | All the following symbols expand to an expression that can be tested in |
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76 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
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77 | ensure it's either C<0> or C<1> if you need that). |
71 | |
78 | |
72 | =over 4 |
79 | =over 4 |
73 | |
80 | |
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81 | =item ECB_C |
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82 | |
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83 | True if the implementation defines the C<__STDC__> macro to a true value, |
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84 | while not claiming to be C++. |
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85 | |
74 | =item ECB_C99 |
86 | =item ECB_C99 |
75 | |
87 | |
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88 | True if the implementation claims to be compliant to C99 (ISO/IEC |
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89 | 9899:1999) or any later version, while not claiming to be C++. |
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90 | |
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91 | Note that later versions (ECB_C11) remove core features again (for |
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92 | example, variable length arrays). |
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93 | |
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94 | =item ECB_C11 |
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95 | |
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96 | True if the implementation claims to be compliant to C11 (ISO/IEC |
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97 | 9899:2011) or any later version, while not claiming to be C++. |
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98 | |
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99 | =item ECB_CPP |
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100 | |
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101 | True if the implementation defines the C<__cplusplus__> macro to a true |
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102 | value, which is typically true for C++ compilers. |
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103 | |
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104 | =item ECB_CPP11 |
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105 | |
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106 | True if the implementation claims to be compliant to ISO/IEC 14882:2011 |
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107 | (C++11) or any later version. |
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108 | |
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109 | =item ECB_GCC_VERSION (major, minor) |
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110 | |
76 | Expands to a true value (suitable for testing in by the preprocessor) |
111 | Expands to a true value (suitable for testing in by the preprocessor) |
77 | if the environment claims to be C99 compliant. |
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78 | |
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79 | =item ECB_C11 |
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80 | |
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81 | Expands to a true value (suitable for testing in by the preprocessor) |
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82 | if the environment claims to be C11 compliant. |
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83 | |
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84 | =item ECB_GCC_VERSION(major,minor) |
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85 | |
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86 | Expands to a true value (suitable for testing in by the preprocessor) |
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87 | if the compiler used is GNU C and the version is the givne version, or |
112 | if the compiler used is GNU C and the version is the given version, or |
88 | higher. |
113 | higher. |
89 | |
114 | |
90 | This macro tries to return false on compilers that claim to be GCC |
115 | This macro tries to return false on compilers that claim to be GCC |
91 | compatible but aren't. |
116 | compatible but aren't. |
92 | |
117 | |
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118 | =item ECB_EXTERN_C |
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119 | |
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120 | Expands to C<extern "C"> in C++, and a simple C<extern> in C. |
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121 | |
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122 | This can be used to declare a single external C function: |
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123 | |
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124 | ECB_EXTERN_C int printf (const char *format, ...); |
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125 | |
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126 | =item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END |
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127 | |
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128 | These two macros can be used to wrap multiple C<extern "C"> definitions - |
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129 | they expand to nothing in C. |
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130 | |
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131 | They are most useful in header files: |
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132 | |
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133 | ECB_EXTERN_C_BEG |
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134 | |
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135 | int mycfun1 (int x); |
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136 | int mycfun2 (int x); |
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137 | |
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138 | ECB_EXTERN_C_END |
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139 | |
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140 | =item ECB_STDFP |
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141 | |
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142 | If this evaluates to a true value (suitable for testing in by the |
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143 | preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
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144 | and double/binary64 representations internally I<and> the endianness of |
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145 | both types match the endianness of C<uint32_t> and C<uint64_t>. |
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146 | |
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147 | This means you can just copy the bits of a C<float> (or C<double>) to an |
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148 | C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation |
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149 | without having to think about format or endianness. |
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150 | |
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151 | This is true for basically all modern platforms, although F<ecb.h> might |
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152 | not be able to deduce this correctly everywhere and might err on the safe |
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153 | side. |
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154 | |
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155 | =item ECB_AMD64, ECB_AMD64_X32 |
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156 | |
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157 | These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
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158 | ABI, respectively, and undefined elsewhere. |
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159 | |
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160 | The designers of the new X32 ABI for some inexplicable reason decided to |
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161 | make it look exactly like amd64, even though it's completely incompatible |
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162 | to that ABI, breaking about every piece of software that assumed that |
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163 | C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
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164 | necessary. |
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165 | |
93 | =back |
166 | =back |
94 | |
167 | |
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168 | =head2 MACRO TRICKERY |
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169 | |
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170 | =over 4 |
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171 | |
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172 | =item ECB_CONCAT (a, b) |
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173 | |
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174 | Expands any macros in C<a> and C<b>, then concatenates the result to form |
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175 | a single token. This is mainly useful to form identifiers from components, |
|
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176 | e.g.: |
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177 | |
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178 | #define S1 str |
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179 | #define S2 cpy |
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180 | |
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181 | ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src); |
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182 | |
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183 | =item ECB_STRINGIFY (arg) |
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184 | |
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185 | Expands any macros in C<arg> and returns the stringified version of |
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186 | it. This is mainly useful to get the contents of a macro in string form, |
|
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187 | e.g.: |
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188 | |
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189 | #define SQL_LIMIT 100 |
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190 | sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); |
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191 | |
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192 | =item ECB_STRINGIFY_EXPR (expr) |
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193 | |
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194 | Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it |
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195 | is a valid expression. This is useful to catch typos or cases where the |
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196 | macro isn't available: |
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197 | |
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198 | #include <errno.h> |
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199 | |
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200 | ECB_STRINGIFY (EDOM); // "33" (on my system at least) |
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201 | ECB_STRINGIFY_EXPR (EDOM); // "33" |
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202 | |
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203 | // now imagine we had a typo: |
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204 | |
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205 | ECB_STRINGIFY (EDAM); // "EDAM" |
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206 | ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined |
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207 | |
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208 | =back |
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209 | |
95 | =head2 GCC ATTRIBUTES |
210 | =head2 ATTRIBUTES |
96 | |
211 | |
97 | A major part of libecb deals with GCC attributes. These are additional |
212 | A major part of libecb deals with additional attributes that can be |
98 | attributes that you can assign to functions, variables and sometimes even |
213 | assigned to functions, variables and sometimes even types - much like |
99 | types - much like C<const> or C<volatile> in C. |
214 | C<const> or C<volatile> in C. They are implemented using either GCC |
100 | |
215 | attributes or other compiler/language specific features. Attributes |
101 | While GCC allows declarations to show up in many surprising places, |
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102 | but not in many expected places, the safest way is to put attribute |
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103 | declarations before the whole declaration: |
216 | declarations must be put before the whole declaration: |
104 | |
217 | |
105 | ecb_const int mysqrt (int a); |
218 | ecb_const int mysqrt (int a); |
106 | ecb_unused int i; |
219 | ecb_unused int i; |
107 | |
220 | |
108 | For variables, it is often nicer to put the attribute after the name, and |
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109 | avoid multiple declarations using commas: |
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110 | |
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111 | int i ecb_unused; |
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112 | |
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113 | =over 4 |
221 | =over 4 |
114 | |
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115 | =item ecb_attribute ((attrs...)) |
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116 | |
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117 | A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to |
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118 | nothing on other compilers, so the effect is that only GCC sees these. |
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119 | |
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120 | Example: use the C<deprecated> attribute on a function. |
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121 | |
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122 | ecb_attribute((__deprecated__)) void |
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123 | do_not_use_me_anymore (void); |
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124 | |
222 | |
125 | =item ecb_unused |
223 | =item ecb_unused |
126 | |
224 | |
127 | Marks a function or a variable as "unused", which simply suppresses a |
225 | Marks a function or a variable as "unused", which simply suppresses a |
128 | warning by GCC when it detects it as unused. This is useful when you e.g. |
226 | warning by GCC when it detects it as unused. This is useful when you e.g. |
129 | declare a variable but do not always use it: |
227 | declare a variable but do not always use it: |
130 | |
228 | |
131 | { |
229 | { |
132 | int var ecb_unused; |
230 | ecb_unused int var; |
133 | |
231 | |
134 | #ifdef SOMECONDITION |
232 | #ifdef SOMECONDITION |
135 | var = ...; |
233 | var = ...; |
136 | return var; |
234 | return var; |
137 | #else |
235 | #else |
138 | return 0; |
236 | return 0; |
139 | #endif |
237 | #endif |
140 | } |
238 | } |
141 | |
239 | |
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240 | =item ecb_deprecated |
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241 | |
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242 | Similar to C<ecb_unused>, but marks a function, variable or type as |
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243 | deprecated. This makes some compilers warn when the type is used. |
|
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244 | |
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245 | =item ecb_deprecated_message (message) |
|
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246 | |
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247 | Same as C<ecb_deprecated>, but if possible, supplies a diagnostic that is |
|
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248 | used instead of a generic depreciation message when the object is being |
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249 | used. |
|
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250 | |
142 | =item ecb_inline |
251 | =item ecb_inline |
143 | |
252 | |
144 | This is not actually an attribute, but you use it like one. It expands |
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145 | either to C<static inline> or to just C<static>, if inline isn't |
253 | Expands either to C<static inline> or to just C<static>, if inline |
146 | supported. It should be used to declare functions that should be inlined, |
254 | isn't supported. It should be used to declare functions that should be |
147 | for code size or speed reasons. |
255 | inlined, for code size or speed reasons. |
148 | |
256 | |
149 | Example: inline this function, it surely will reduce codesize. |
257 | Example: inline this function, it surely will reduce codesize. |
150 | |
258 | |
151 | ecb_inline int |
259 | ecb_inline int |
152 | negmul (int a, int b) |
260 | negmul (int a, int b) |
… | |
… | |
154 | return - (a * b); |
262 | return - (a * b); |
155 | } |
263 | } |
156 | |
264 | |
157 | =item ecb_noinline |
265 | =item ecb_noinline |
158 | |
266 | |
159 | Prevent a function from being inlined - it might be optimised away, but |
267 | Prevents a function from being inlined - it might be optimised away, but |
160 | not inlined into other functions. This is useful if you know your function |
268 | not inlined into other functions. This is useful if you know your function |
161 | is rarely called and large enough for inlining not to be helpful. |
269 | is rarely called and large enough for inlining not to be helpful. |
162 | |
270 | |
163 | =item ecb_noreturn |
271 | =item ecb_noreturn |
164 | |
272 | |
… | |
… | |
174 | } |
282 | } |
175 | |
283 | |
176 | In this case, the compiler would probably be smart enough to deduce it on |
284 | In this case, the compiler would probably be smart enough to deduce it on |
177 | its own, so this is mainly useful for declarations. |
285 | its own, so this is mainly useful for declarations. |
178 | |
286 | |
|
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287 | =item ecb_restrict |
|
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288 | |
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289 | Expands to the C<restrict> keyword or equivalent on compilers that support |
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290 | them, and to nothing on others. Must be specified on a pointer type or |
|
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291 | an array index to indicate that the memory doesn't alias with any other |
|
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292 | restricted pointer in the same scope. |
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293 | |
|
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294 | Example: multiply a vector, and allow the compiler to parallelise the |
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295 | loop, because it knows it doesn't overwrite input values. |
|
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296 | |
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297 | void |
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298 | multiply (ecb_restrict float *src, |
|
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299 | ecb_restrict float *dst, |
|
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300 | int len, float factor) |
|
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301 | { |
|
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302 | int i; |
|
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303 | |
|
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304 | for (i = 0; i < len; ++i) |
|
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305 | dst [i] = src [i] * factor; |
|
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306 | } |
|
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307 | |
179 | =item ecb_const |
308 | =item ecb_const |
180 | |
309 | |
181 | Declares that the function only depends on the values of its arguments, |
310 | Declares that the function only depends on the values of its arguments, |
182 | much like a mathematical function. It specifically does not read or write |
311 | much like a mathematical function. It specifically does not read or write |
183 | any memory any arguments might point to, global variables, or call any |
312 | any memory any arguments might point to, global variables, or call any |
… | |
… | |
243 | functions only called in exceptional or rare cases. |
372 | functions only called in exceptional or rare cases. |
244 | |
373 | |
245 | =item ecb_artificial |
374 | =item ecb_artificial |
246 | |
375 | |
247 | Declares the function as "artificial", in this case meaning that this |
376 | Declares the function as "artificial", in this case meaning that this |
248 | function is not really mean to be a function, but more like an accessor |
377 | function is not really meant to be a function, but more like an accessor |
249 | - many methods in C++ classes are mere accessor functions, and having a |
378 | - many methods in C++ classes are mere accessor functions, and having a |
250 | crash reported in such a method, or single-stepping through them, is not |
379 | crash reported in such a method, or single-stepping through them, is not |
251 | usually so helpful, especially when it's inlined to just a few instructions. |
380 | usually so helpful, especially when it's inlined to just a few instructions. |
252 | |
381 | |
253 | Marking them as artificial will instruct the debugger about just this, |
382 | Marking them as artificial will instruct the debugger about just this, |
… | |
… | |
273 | |
402 | |
274 | =head2 OPTIMISATION HINTS |
403 | =head2 OPTIMISATION HINTS |
275 | |
404 | |
276 | =over 4 |
405 | =over 4 |
277 | |
406 | |
278 | =item bool ecb_is_constant(expr) |
407 | =item bool ecb_is_constant (expr) |
279 | |
408 | |
280 | Returns true iff the expression can be deduced to be a compile-time |
409 | Returns true iff the expression can be deduced to be a compile-time |
281 | constant, and false otherwise. |
410 | constant, and false otherwise. |
282 | |
411 | |
283 | For example, when you have a C<rndm16> function that returns a 16 bit |
412 | For example, when you have a C<rndm16> function that returns a 16 bit |
… | |
… | |
301 | return is_constant (n) && !(n & (n - 1)) |
430 | return is_constant (n) && !(n & (n - 1)) |
302 | ? rndm16 () & (num - 1) |
431 | ? rndm16 () & (num - 1) |
303 | : (n * (uint32_t)rndm16 ()) >> 16; |
432 | : (n * (uint32_t)rndm16 ()) >> 16; |
304 | } |
433 | } |
305 | |
434 | |
306 | =item bool ecb_expect (expr, value) |
435 | =item ecb_expect (expr, value) |
307 | |
436 | |
308 | Evaluates C<expr> and returns it. In addition, it tells the compiler that |
437 | Evaluates C<expr> and returns it. In addition, it tells the compiler that |
309 | the C<expr> evaluates to C<value> a lot, which can be used for static |
438 | the C<expr> evaluates to C<value> a lot, which can be used for static |
310 | branch optimisations. |
439 | branch optimisations. |
311 | |
440 | |
… | |
… | |
358 | { |
487 | { |
359 | if (ecb_expect_false (current + size > end)) |
488 | if (ecb_expect_false (current + size > end)) |
360 | real_reserve_method (size); /* presumably noinline */ |
489 | real_reserve_method (size); /* presumably noinline */ |
361 | } |
490 | } |
362 | |
491 | |
363 | =item bool ecb_assume (cond) |
492 | =item ecb_assume (cond) |
364 | |
493 | |
365 | Try to tell the compiler that some condition is true, even if it's not |
494 | Tries to tell the compiler that some condition is true, even if it's not |
366 | obvious. |
495 | obvious. This is not a function, but a statement: it cannot be used in |
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496 | another expression. |
367 | |
497 | |
368 | This can be used to teach the compiler about invariants or other |
498 | This can be used to teach the compiler about invariants or other |
369 | conditions that might improve code generation, but which are impossible to |
499 | conditions that might improve code generation, but which are impossible to |
370 | deduce form the code itself. |
500 | deduce form the code itself. |
371 | |
501 | |
… | |
… | |
388 | |
518 | |
389 | Then the compiler I<might> be able to optimise out the second call |
519 | Then the compiler I<might> be able to optimise out the second call |
390 | completely, as it knows that C<< current + 1 > end >> is false and the |
520 | completely, as it knows that C<< current + 1 > end >> is false and the |
391 | call will never be executed. |
521 | call will never be executed. |
392 | |
522 | |
393 | =item bool ecb_unreachable () |
523 | =item ecb_unreachable () |
394 | |
524 | |
395 | This function does nothing itself, except tell the compiler that it will |
525 | This function does nothing itself, except tell the compiler that it will |
396 | never be executed. Apart from suppressing a warning in some cases, this |
526 | never be executed. Apart from suppressing a warning in some cases, this |
397 | function can be used to implement C<ecb_assume> or similar functions. |
527 | function can be used to implement C<ecb_assume> or similar functionality. |
398 | |
528 | |
399 | =item bool ecb_prefetch (addr, rw, locality) |
529 | =item ecb_prefetch (addr, rw, locality) |
400 | |
530 | |
401 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
531 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
402 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
532 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
403 | C<0> means that there will only be one access later, C<3> means that |
533 | C<0> means that there will only be one access later, C<3> means that |
404 | the data will likely be accessed very often, and values in between mean |
534 | the data will likely be accessed very often, and values in between mean |
405 | something... in between. The memory pointed to by the address does not |
535 | something... in between. The memory pointed to by the address does not |
406 | need to be accessible (it could be a null pointer for example), but C<rw> |
536 | need to be accessible (it could be a null pointer for example), but C<rw> |
407 | and C<locality> must be compile-time constants. |
537 | and C<locality> must be compile-time constants. |
408 | |
538 | |
|
|
539 | This is a statement, not a function: you cannot use it as part of an |
|
|
540 | expression. |
|
|
541 | |
409 | An obvious way to use this is to prefetch some data far away, in a big |
542 | An obvious way to use this is to prefetch some data far away, in a big |
410 | array you loop over. This prefetches memory some 128 array elements later, |
543 | array you loop over. This prefetches memory some 128 array elements later, |
411 | in the hope that it will be ready when the CPU arrives at that location. |
544 | in the hope that it will be ready when the CPU arrives at that location. |
412 | |
545 | |
413 | int sum = 0; |
546 | int sum = 0; |
… | |
… | |
465 | |
598 | |
466 | =item bool ecb_is_pot32 (uint32_t x) |
599 | =item bool ecb_is_pot32 (uint32_t x) |
467 | |
600 | |
468 | =item bool ecb_is_pot64 (uint32_t x) |
601 | =item bool ecb_is_pot64 (uint32_t x) |
469 | |
602 | |
470 | Return true iff C<x> is a power of two or C<x == 0>. |
603 | Returns true iff C<x> is a power of two or C<x == 0>. |
471 | |
604 | |
472 | For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. |
605 | For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>. |
473 | |
606 | |
474 | =item int ecb_ld32 (uint32_t x) |
607 | =item int ecb_ld32 (uint32_t x) |
475 | |
608 | |
476 | =item int ecb_ld64 (uint64_t x) |
609 | =item int ecb_ld64 (uint64_t x) |
477 | |
610 | |
… | |
… | |
546 | (C<ecb_rotl>). |
679 | (C<ecb_rotl>). |
547 | |
680 | |
548 | Current GCC versions understand these functions and usually compile them |
681 | Current GCC versions understand these functions and usually compile them |
549 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
682 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
550 | x86). |
683 | x86). |
|
|
684 | |
|
|
685 | =back |
|
|
686 | |
|
|
687 | =head2 FLOATING POINT FIDDLING |
|
|
688 | |
|
|
689 | =over 4 |
|
|
690 | |
|
|
691 | =item ECB_INFINITY |
|
|
692 | |
|
|
693 | Evaluates to positive infinity if supported by the platform, otherwise to |
|
|
694 | a truly huge number. |
|
|
695 | |
|
|
696 | =item ECB_NAN |
|
|
697 | |
|
|
698 | Evaluates to a quiet NAN if supported by the platform, otherwise to |
|
|
699 | C<ECB_INFINITY>. |
|
|
700 | |
|
|
701 | =item float ecb_ldexpf (float x, int exp) |
|
|
702 | |
|
|
703 | Same as C<ldexpf>, but always available. |
|
|
704 | |
|
|
705 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
|
|
706 | |
|
|
707 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
|
|
708 | |
|
|
709 | These functions each take an argument in the native C<float> or C<double> |
|
|
710 | type and return the IEEE 754 bit representation of it. |
|
|
711 | |
|
|
712 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
|
|
713 | will be the most significant bit, followed by exponent and mantissa. |
|
|
714 | |
|
|
715 | This function should work even when the native floating point format isn't |
|
|
716 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
717 | also within reasonable limits (it tries to convert NaNs, infinities and |
|
|
718 | denormals, but will likely convert negative zero to positive zero). |
|
|
719 | |
|
|
720 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
721 | be able to optimise away this function completely. |
|
|
722 | |
|
|
723 | These functions can be helpful when serialising floats to the network - you |
|
|
724 | can serialise the return value like a normal uint32_t/uint64_t. |
|
|
725 | |
|
|
726 | Another use for these functions is to manipulate floating point values |
|
|
727 | directly. |
|
|
728 | |
|
|
729 | Silly example: toggle the sign bit of a float. |
|
|
730 | |
|
|
731 | /* On gcc-4.7 on amd64, */ |
|
|
732 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
|
|
733 | /* instructions to move the float value to an integer register and back. */ |
|
|
734 | |
|
|
735 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
|
|
736 | |
|
|
737 | =item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] |
|
|
738 | |
|
|
739 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
|
|
740 | |
|
|
741 | =item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] |
|
|
742 | |
|
|
743 | The reverse operation of the previous function - takes the bit |
|
|
744 | representation of an IEEE binary16, binary32 or binary64 number and |
|
|
745 | converts it to the native C<float> or C<double> format. |
|
|
746 | |
|
|
747 | This function should work even when the native floating point format isn't |
|
|
748 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
749 | also within reasonable limits (it tries to convert normals and denormals, |
|
|
750 | and might be lucky for infinities, and with extraordinary luck, also for |
|
|
751 | negative zero). |
|
|
752 | |
|
|
753 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
754 | be able to optimise away this function completely. |
551 | |
755 | |
552 | =back |
756 | =back |
553 | |
757 | |
554 | =head2 ARITHMETIC |
758 | =head2 ARITHMETIC |
555 | |
759 | |
… | |
… | |
612 | |
816 | |
613 | These symbols need to be defined before including F<ecb.h> the first time. |
817 | These symbols need to be defined before including F<ecb.h> the first time. |
614 | |
818 | |
615 | =over 4 |
819 | =over 4 |
616 | |
820 | |
617 | =item ECB_NO_THRADS |
821 | =item ECB_NO_THREADS |
618 | |
822 | |
619 | If F<ecb.h> is never used from multiple threads, then this symbol can |
823 | If F<ecb.h> is never used from multiple threads, then this symbol can |
620 | be defined, in which case memory fences (and similar constructs) are |
824 | be defined, in which case memory fences (and similar constructs) are |
621 | completely removed, leading to more efficient code and fewer dependencies. |
825 | completely removed, leading to more efficient code and fewer dependencies. |
622 | |
826 | |
… | |
… | |
628 | multiple threads, but never concurrently (e.g. if the system the program |
832 | multiple threads, but never concurrently (e.g. if the system the program |
629 | runs on has only a single CPU with a single core, no hyperthreading and so |
833 | runs on has only a single CPU with a single core, no hyperthreading and so |
630 | on), then this symbol can be defined, leading to more efficient code and |
834 | on), then this symbol can be defined, leading to more efficient code and |
631 | fewer dependencies. |
835 | fewer dependencies. |
632 | |
836 | |
|
|
837 | =item ECB_NO_LIBM |
|
|
838 | |
|
|
839 | When defined to C<1>, do not export any functions that might introduce |
|
|
840 | dependencies on the math library (usually called F<-lm>) - these are |
|
|
841 | marked with [-UECB_NO_LIBM]. |
|
|
842 | |
633 | =back |
843 | =back |
634 | |
844 | |
635 | |
845 | |