… | |
… | |
54 | only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
54 | only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
55 | the corresponding function relies on C to implement the correct types, and |
55 | the corresponding function relies on C to implement the correct types, and |
56 | is usually implemented as a macro. Specifically, a "bool" in this manual |
56 | is usually implemented as a macro. Specifically, a "bool" in this manual |
57 | refers to any kind of boolean value, not a specific type. |
57 | refers to any kind of boolean value, not a specific type. |
58 | |
58 | |
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59 | =head2 TYPES / TYPE SUPPORT |
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60 | |
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61 | ecb.h makes sure that the following types are defined (in the expected way): |
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62 | |
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63 | int8_t uint8_t int16_t uint16_t |
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64 | int32_t uint32_t int64_t uint64_t |
|
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65 | intptr_t uintptr_t |
|
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66 | |
|
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67 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
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68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
|
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69 | expressions. |
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70 | |
|
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71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
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72 | |
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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). |
|
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78 | |
|
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79 | =over 4 |
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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 | |
|
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86 | =item ECB_C99 |
|
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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 | |
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111 | Expands to a true value (suitable for testing in by the preprocessor) |
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112 | if the compiler used is GNU C and the version is the given version, or |
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113 | higher. |
|
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114 | |
|
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115 | This macro tries to return false on compilers that claim to be GCC |
|
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116 | compatible but aren't. |
|
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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 | |
|
|
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 | |
|
|
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 | |
|
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166 | =back |
|
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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, |
|
|
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 | |
|
|
185 | Expands any macros in C<arg> and returns the stringified version of |
|
|
186 | it. This is mainly useful to get the contents of a macro in string form, |
|
|
187 | e.g.: |
|
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188 | |
|
|
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 |
|
|
195 | is a valid expression. This is useful to catch typos or cases where the |
|
|
196 | macro isn't available: |
|
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197 | |
|
|
198 | #include <errno.h> |
|
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199 | |
|
|
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 | |
|
|
203 | // now imagine we had a typo: |
|
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204 | |
|
|
205 | ECB_STRINGIFY (EDAM); // "EDAM" |
|
|
206 | ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined |
|
|
207 | |
|
|
208 | =back |
|
|
209 | |
59 | =head2 GCC ATTRIBUTES |
210 | =head2 ATTRIBUTES |
60 | |
211 | |
61 | 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 |
62 | attributes that you can assign to functions, variables and sometimes even |
213 | assigned to functions, variables and sometimes even types - much like |
63 | types - much like C<const> or C<volatile> in C. |
214 | C<const> or C<volatile> in C. They are implemented using either GCC |
64 | |
215 | attributes or other compiler/language specific features. Attributes |
65 | While GCC allows declarations to show up in many surprising places, |
|
|
66 | but not in many expected places, the safest way is to put attribute |
|
|
67 | declarations before the whole declaration: |
216 | declarations must be put before the whole declaration: |
68 | |
217 | |
69 | ecb_const int mysqrt (int a); |
218 | ecb_const int mysqrt (int a); |
70 | ecb_unused int i; |
219 | ecb_unused int i; |
71 | |
220 | |
72 | For variables, it is often nicer to put the attribute after the name, and |
|
|
73 | avoid multiple declarations using commas: |
|
|
74 | |
|
|
75 | int i ecb_unused; |
|
|
76 | |
|
|
77 | =over 4 |
221 | =over 4 |
78 | |
|
|
79 | =item ecb_attribute ((attrs...)) |
|
|
80 | |
|
|
81 | A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to |
|
|
82 | nothing on other compilers, so the effect is that only GCC sees these. |
|
|
83 | |
|
|
84 | Example: use the C<deprecated> attribute on a function. |
|
|
85 | |
|
|
86 | ecb_attribute((__deprecated__)) void |
|
|
87 | do_not_use_me_anymore (void); |
|
|
88 | |
222 | |
89 | =item ecb_unused |
223 | =item ecb_unused |
90 | |
224 | |
91 | 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 |
92 | 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. |
93 | declare a variable but do not always use it: |
227 | declare a variable but do not always use it: |
94 | |
228 | |
95 | { |
229 | { |
96 | int var ecb_unused; |
230 | ecb_unused int var; |
97 | |
231 | |
98 | #ifdef SOMECONDITION |
232 | #ifdef SOMECONDITION |
99 | var = ...; |
233 | var = ...; |
100 | return var; |
234 | return var; |
101 | #else |
235 | #else |
102 | return 0; |
236 | return 0; |
103 | #endif |
237 | #endif |
104 | } |
238 | } |
105 | |
239 | |
|
|
240 | =item ecb_deprecated |
|
|
241 | |
|
|
242 | Similar to C<ecb_unused>, but marks a function, variable or type as |
|
|
243 | deprecated. This makes some compilers warn when the type is used. |
|
|
244 | |
|
|
245 | =item ecb_deprecated_message (message) |
|
|
246 | |
|
|
247 | Same as C<ecb_deprecated>, but if possible, the specified diagnostic is |
|
|
248 | used instead of a generic depreciation message when the object is being |
|
|
249 | used. |
|
|
250 | |
|
|
251 | =item ecb_inline |
|
|
252 | |
|
|
253 | Expands either to C<static inline> or to just C<static>, if inline |
|
|
254 | isn't supported. It should be used to declare functions that should be |
|
|
255 | inlined, for code size or speed reasons. |
|
|
256 | |
|
|
257 | Example: inline this function, it surely will reduce codesize. |
|
|
258 | |
|
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259 | ecb_inline int |
|
|
260 | negmul (int a, int b) |
|
|
261 | { |
|
|
262 | return - (a * b); |
|
|
263 | } |
|
|
264 | |
106 | =item ecb_noinline |
265 | =item ecb_noinline |
107 | |
266 | |
108 | 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 |
109 | 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 |
110 | 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. |
111 | |
270 | |
112 | =item ecb_noreturn |
271 | =item ecb_noreturn |
113 | |
272 | |
… | |
… | |
123 | } |
282 | } |
124 | |
283 | |
125 | 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 |
126 | its own, so this is mainly useful for declarations. |
285 | its own, so this is mainly useful for declarations. |
127 | |
286 | |
|
|
287 | =item ecb_restrict |
|
|
288 | |
|
|
289 | Expands to the C<restrict> keyword or equivalent on compilers that support |
|
|
290 | them, and to nothing on others. Must be specified on a pointer type or |
|
|
291 | an array index to indicate that the memory doesn't alias with any other |
|
|
292 | restricted pointer in the same scope. |
|
|
293 | |
|
|
294 | Example: multiply a vector, and allow the compiler to parallelise the |
|
|
295 | loop, because it knows it doesn't overwrite input values. |
|
|
296 | |
|
|
297 | void |
|
|
298 | multiply (ecb_restrict float *src, |
|
|
299 | ecb_restrict float *dst, |
|
|
300 | int len, float factor) |
|
|
301 | { |
|
|
302 | int i; |
|
|
303 | |
|
|
304 | for (i = 0; i < len; ++i) |
|
|
305 | dst [i] = src [i] * factor; |
|
|
306 | } |
|
|
307 | |
128 | =item ecb_const |
308 | =item ecb_const |
129 | |
309 | |
130 | 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, |
131 | 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 |
132 | 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 |
… | |
… | |
192 | functions only called in exceptional or rare cases. |
372 | functions only called in exceptional or rare cases. |
193 | |
373 | |
194 | =item ecb_artificial |
374 | =item ecb_artificial |
195 | |
375 | |
196 | Declares the function as "artificial", in this case meaning that this |
376 | Declares the function as "artificial", in this case meaning that this |
197 | 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 |
198 | - 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 |
199 | 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 |
200 | 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. |
201 | |
381 | |
202 | Marking them as artificial will instruct the debugger about just this, |
382 | Marking them as artificial will instruct the debugger about just this, |
… | |
… | |
222 | |
402 | |
223 | =head2 OPTIMISATION HINTS |
403 | =head2 OPTIMISATION HINTS |
224 | |
404 | |
225 | =over 4 |
405 | =over 4 |
226 | |
406 | |
227 | =item bool ecb_is_constant(expr) |
407 | =item bool ecb_is_constant (expr) |
228 | |
408 | |
229 | 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 |
230 | constant, and false otherwise. |
410 | constant, and false otherwise. |
231 | |
411 | |
232 | 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 |
… | |
… | |
250 | return is_constant (n) && !(n & (n - 1)) |
430 | return is_constant (n) && !(n & (n - 1)) |
251 | ? rndm16 () & (num - 1) |
431 | ? rndm16 () & (num - 1) |
252 | : (n * (uint32_t)rndm16 ()) >> 16; |
432 | : (n * (uint32_t)rndm16 ()) >> 16; |
253 | } |
433 | } |
254 | |
434 | |
255 | =item bool ecb_expect (expr, value) |
435 | =item ecb_expect (expr, value) |
256 | |
436 | |
257 | 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 |
258 | 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 |
259 | branch optimisations. |
439 | branch optimisations. |
260 | |
440 | |
… | |
… | |
307 | { |
487 | { |
308 | if (ecb_expect_false (current + size > end)) |
488 | if (ecb_expect_false (current + size > end)) |
309 | real_reserve_method (size); /* presumably noinline */ |
489 | real_reserve_method (size); /* presumably noinline */ |
310 | } |
490 | } |
311 | |
491 | |
312 | =item bool ecb_assume (cond) |
492 | =item ecb_assume (cond) |
313 | |
493 | |
314 | 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 |
315 | obvious. |
495 | obvious. This is not a function, but a statement: it cannot be used in |
|
|
496 | another expression. |
316 | |
497 | |
317 | 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 |
318 | conditions that might improve code generation, but which are impossible to |
499 | conditions that might improve code generation, but which are impossible to |
319 | deduce form the code itself. |
500 | deduce form the code itself. |
320 | |
501 | |
… | |
… | |
337 | |
518 | |
338 | 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 |
339 | 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 |
340 | call will never be executed. |
521 | call will never be executed. |
341 | |
522 | |
342 | =item bool ecb_unreachable () |
523 | =item ecb_unreachable () |
343 | |
524 | |
344 | 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 |
345 | 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 |
346 | 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. |
347 | |
528 | |
348 | =item bool ecb_prefetch (addr, rw, locality) |
529 | =item ecb_prefetch (addr, rw, locality) |
349 | |
530 | |
350 | 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 |
351 | 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 |
352 | 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 |
353 | 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 |
354 | 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 |
355 | 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> |
356 | and C<locality> must be compile-time constants. |
537 | and C<locality> must be compile-time constants. |
357 | |
538 | |
|
|
539 | This is a statement, not a function: you cannot use it as part of an |
|
|
540 | expression. |
|
|
541 | |
358 | 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 |
359 | 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, |
360 | 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. |
361 | |
545 | |
362 | int sum = 0; |
546 | int sum = 0; |
… | |
… | |
381 | After processing the node, (part of) the next node might already be in |
565 | After processing the node, (part of) the next node might already be in |
382 | cache. |
566 | cache. |
383 | |
567 | |
384 | =back |
568 | =back |
385 | |
569 | |
386 | =head2 BIT FIDDLING / BITSTUFFS |
570 | =head2 BIT FIDDLING / BIT WIZARDRY |
387 | |
571 | |
388 | =over 4 |
572 | =over 4 |
389 | |
573 | |
390 | =item bool ecb_big_endian () |
574 | =item bool ecb_big_endian () |
391 | |
575 | |
… | |
… | |
397 | |
581 | |
398 | On systems that are neither, their return values are unspecified. |
582 | On systems that are neither, their return values are unspecified. |
399 | |
583 | |
400 | =item int ecb_ctz32 (uint32_t x) |
584 | =item int ecb_ctz32 (uint32_t x) |
401 | |
585 | |
|
|
586 | =item int ecb_ctz64 (uint64_t x) |
|
|
587 | |
402 | Returns the index of the least significant bit set in C<x> (or |
588 | Returns the index of the least significant bit set in C<x> (or |
403 | equivalently the number of bits set to 0 before the least significant bit |
589 | equivalently the number of bits set to 0 before the least significant bit |
404 | set), starting from 0. If C<x> is 0 the result is undefined. A common use |
590 | set), starting from 0. If C<x> is 0 the result is undefined. |
405 | case is to compute the integer binary logarithm, i.e., C<floor (log2 |
591 | |
|
|
592 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
|
|
593 | |
406 | (n))>. For example: |
594 | For example: |
407 | |
595 | |
408 | ecb_ctz32 (3) = 0 |
596 | ecb_ctz32 (3) = 0 |
409 | ecb_ctz32 (6) = 1 |
597 | ecb_ctz32 (6) = 1 |
410 | |
598 | |
|
|
599 | =item bool ecb_is_pot32 (uint32_t x) |
|
|
600 | |
|
|
601 | =item bool ecb_is_pot64 (uint32_t x) |
|
|
602 | |
|
|
603 | Returns true iff C<x> is a power of two or C<x == 0>. |
|
|
604 | |
|
|
605 | For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>. |
|
|
606 | |
|
|
607 | =item int ecb_ld32 (uint32_t x) |
|
|
608 | |
|
|
609 | =item int ecb_ld64 (uint64_t x) |
|
|
610 | |
|
|
611 | Returns the index of the most significant bit set in C<x>, or the number |
|
|
612 | of digits the number requires in binary (so that C<< 2**ld <= x < |
|
|
613 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
|
|
614 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
|
|
615 | example to see how many bits a certain number requires to be encoded. |
|
|
616 | |
|
|
617 | This function is similar to the "count leading zero bits" function, except |
|
|
618 | that that one returns how many zero bits are "in front" of the number (in |
|
|
619 | the given data type), while C<ecb_ld> returns how many bits the number |
|
|
620 | itself requires. |
|
|
621 | |
|
|
622 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
|
|
623 | |
411 | =item int ecb_popcount32 (uint32_t x) |
624 | =item int ecb_popcount32 (uint32_t x) |
412 | |
625 | |
|
|
626 | =item int ecb_popcount64 (uint64_t x) |
|
|
627 | |
413 | Returns the number of bits set to 1 in C<x>. For example: |
628 | Returns the number of bits set to 1 in C<x>. |
|
|
629 | |
|
|
630 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
|
|
631 | |
|
|
632 | For example: |
414 | |
633 | |
415 | ecb_popcount32 (7) = 3 |
634 | ecb_popcount32 (7) = 3 |
416 | ecb_popcount32 (255) = 8 |
635 | ecb_popcount32 (255) = 8 |
417 | |
636 | |
|
|
637 | =item uint8_t ecb_bitrev8 (uint8_t x) |
|
|
638 | |
|
|
639 | =item uint16_t ecb_bitrev16 (uint16_t x) |
|
|
640 | |
|
|
641 | =item uint32_t ecb_bitrev32 (uint32_t x) |
|
|
642 | |
|
|
643 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
|
|
644 | and so on. |
|
|
645 | |
|
|
646 | Example: |
|
|
647 | |
|
|
648 | ecb_bitrev8 (0xa7) = 0xea |
|
|
649 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
|
|
650 | |
418 | =item uint32_t ecb_bswap16 (uint32_t x) |
651 | =item uint32_t ecb_bswap16 (uint32_t x) |
419 | |
652 | |
420 | =item uint32_t ecb_bswap32 (uint32_t x) |
653 | =item uint32_t ecb_bswap32 (uint32_t x) |
421 | |
654 | |
|
|
655 | =item uint64_t ecb_bswap64 (uint64_t x) |
|
|
656 | |
422 | These two functions return the value of the 16-bit (32-bit) value C<x> |
657 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
423 | after reversing the order of bytes (0x11223344 becomes 0x44332211). |
658 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
|
|
659 | C<ecb_bswap32>). |
|
|
660 | |
|
|
661 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
|
|
662 | |
|
|
663 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
|
|
664 | |
|
|
665 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
|
|
666 | |
|
|
667 | =item uint64_t ecb_rotl64 (uint64_t x, unsigned int count) |
|
|
668 | |
|
|
669 | =item uint8_t ecb_rotr8 (uint8_t x, unsigned int count) |
|
|
670 | |
|
|
671 | =item uint16_t ecb_rotr16 (uint16_t x, unsigned int count) |
424 | |
672 | |
425 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
673 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
426 | |
674 | |
427 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
675 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
428 | |
676 | |
429 | These two functions return the value of C<x> after rotating all the bits |
677 | These two families of functions return the value of C<x> after rotating |
430 | by C<count> positions to the right or left respectively. |
678 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
|
|
679 | (C<ecb_rotl>). |
431 | |
680 | |
432 | Current GCC versions understand these functions and usually compile them |
681 | Current GCC versions understand these functions and usually compile them |
433 | to "optimal" code (e.g. a single C<roll> on x86). |
682 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
|
|
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_binary64_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. |
434 | |
755 | |
435 | =back |
756 | =back |
436 | |
757 | |
437 | =head2 ARITHMETIC |
758 | =head2 ARITHMETIC |
438 | |
759 | |
… | |
… | |
448 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
769 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
449 | in the language. |
770 | in the language. |
450 | |
771 | |
451 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
772 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
452 | negatable, that is, both C<m> and C<-m> must be representable in its |
773 | negatable, that is, both C<m> and C<-m> must be representable in its |
453 | type (this typically includes the minimum signed integer value, the same |
774 | type (this typically excludes the minimum signed integer value, the same |
454 | limitation as for C</> and C<%> in C). |
775 | limitation as for C</> and C<%> in C). |
455 | |
776 | |
456 | Current GCC versions compile this into an efficient branchless sequence on |
777 | Current GCC versions compile this into an efficient branchless sequence on |
457 | almost all CPUs. |
778 | almost all CPUs. |
458 | |
779 | |
… | |
… | |
462 | change direction for negative values: |
783 | change direction for negative values: |
463 | |
784 | |
464 | for (m = -100; m <= 100; ++m) |
785 | for (m = -100; m <= 100; ++m) |
465 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
786 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
466 | |
787 | |
|
|
788 | =item x = ecb_div_rd (val, div) |
|
|
789 | |
|
|
790 | =item x = ecb_div_ru (val, div) |
|
|
791 | |
|
|
792 | Returns C<val> divided by C<div> rounded down or up, respectively. |
|
|
793 | C<val> and C<div> must have integer types and C<div> must be strictly |
|
|
794 | positive. Note that these functions are implemented with macros in C |
|
|
795 | and with function templates in C++. |
|
|
796 | |
467 | =back |
797 | =back |
468 | |
798 | |
469 | =head2 UTILITY |
799 | =head2 UTILITY |
470 | |
800 | |
471 | =over 4 |
801 | =over 4 |
… | |
… | |
480 | for (i = 0; i < ecb_array_length (primes); i++) |
810 | for (i = 0; i < ecb_array_length (primes); i++) |
481 | sum += primes [i]; |
811 | sum += primes [i]; |
482 | |
812 | |
483 | =back |
813 | =back |
484 | |
814 | |
|
|
815 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
485 | |
816 | |
|
|
817 | These symbols need to be defined before including F<ecb.h> the first time. |
|
|
818 | |
|
|
819 | =over 4 |
|
|
820 | |
|
|
821 | =item ECB_NO_THREADS |
|
|
822 | |
|
|
823 | If F<ecb.h> is never used from multiple threads, then this symbol can |
|
|
824 | be defined, in which case memory fences (and similar constructs) are |
|
|
825 | completely removed, leading to more efficient code and fewer dependencies. |
|
|
826 | |
|
|
827 | Setting this symbol to a true value implies C<ECB_NO_SMP>. |
|
|
828 | |
|
|
829 | =item ECB_NO_SMP |
|
|
830 | |
|
|
831 | The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from |
|
|
832 | multiple threads, but never concurrently (e.g. if the system the program |
|
|
833 | runs on has only a single CPU with a single core, no hyperthreading and so |
|
|
834 | on), then this symbol can be defined, leading to more efficient code and |
|
|
835 | fewer dependencies. |
|
|
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 | |
|
|
843 | =back |
|
|
844 | |
|
|
845 | =head1 UNDOCUMENTED FUNCTIONALITY |
|
|
846 | |
|
|
847 | F<ecb.h> is full of undocumented functionality as well, some of which is |
|
|
848 | intended to be internal-use only, some of which we forgot to document, and |
|
|
849 | some of which we hide because we are not sure we will keep the interface |
|
|
850 | stable. |
|
|
851 | |
|
|
852 | While you are welcome to rummage around and use whatever you find useful |
|
|
853 | (we can't stop you), keep in mind that we will change undocumented |
|
|
854 | functionality in incompatible ways without thinking twice, while we are |
|
|
855 | considerably more conservative with documented things. |
|
|
856 | |
|
|
857 | =head1 AUTHORS |
|
|
858 | |
|
|
859 | C<libecb> is designed and maintained by: |
|
|
860 | |
|
|
861 | Emanuele Giaquinta <e.giaquinta@glauco.it> |
|
|
862 | Marc Alexander Lehmann <schmorp@schmorp.de> |
|
|
863 | |
|
|
864 | |