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1 | =head1 LIBECB - e-C-Builtins |
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1 | =head1 LIBECB |
3 | =head2 ABOUT LIBECB |
2 | |
4 | |
3 | You suck, we don't(tm) |
5 | Libecb is currently a simple header file that doesn't require any |
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6 | configuration to use or include in your project. |
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7 | |
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8 | It's part of the e-suite of libraries, other memembers of which include |
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9 | libev and libeio. |
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10 | |
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11 | Its homepage can be found here: |
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12 | |
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13 | http://software.schmorp.de/pkg/libecb |
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14 | |
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15 | It mainly provides a number of wrappers around GCC built-ins, together |
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16 | with replacement functions for other compilers. In addition to this, |
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17 | it provides a number of other lowlevel C utilities, such endienness |
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18 | detection, byte swapping or bit rotations. |
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19 | |
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20 | More might come. |
4 | |
21 | |
5 | =head2 ABOUT THE HEADER |
22 | =head2 ABOUT THE HEADER |
6 | |
23 | |
7 | - how to include it |
24 | At the moment, all you have to do is copy F<ecb.h> somewhere where your |
8 | - it includes inttypes.h |
25 | compiler can find it and include it: |
9 | - no .a |
26 | |
10 | - whats a bool |
27 | #include <ecb.h> |
11 | - function mean macro or function |
28 | |
12 | - macro means untyped |
29 | The header should work fine for both C and C++ compilation, and gives you |
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30 | all of F<inttypes.h> in addition to the ECB symbols. |
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31 | |
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32 | There are currently no objetc files to link to - future versions might |
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33 | come with an (optional) object code library to link against, to reduce |
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34 | code size or gain access to additional features. |
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35 | |
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36 | It also currently includes everything from F<inttypes.h>. |
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37 | |
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38 | =head2 ABOUT THIS MANUAL / CONVENTIONS |
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39 | |
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40 | This manual mainly describes each (public) function available after |
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41 | including the F<ecb.h> header. The header might define other symbols than |
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42 | these, but these are not part of the public API, and not supported in any |
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43 | way. |
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44 | |
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45 | When the manual mentions a "function" then this could be defined either as |
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46 | as inline function, a macro, or an external symbol. |
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47 | |
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48 | When functions use a concrete standard type, such as C<int> or |
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49 | C<uint32_t>, then the corresponding function works only with that type. If |
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50 | only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
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51 | the corresponding function relies on C to implement the correct types, and |
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52 | is usually implemented as a macro. Specifically, a "bool" in this manual |
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53 | refers to any kind of boolean value, not a specific type. |
13 | |
54 | |
14 | =head2 GCC ATTRIBUTES |
55 | =head2 GCC ATTRIBUTES |
15 | |
56 | |
16 | blabla where to put, what others |
57 | blabla where to put, what others |
17 | |
58 | |
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61 | |
102 | |
62 | =head2 OPTIMISATION HINTS |
103 | =head2 OPTIMISATION HINTS |
63 | |
104 | |
64 | =over 4 |
105 | =over 4 |
65 | |
106 | |
66 | =item bool ecb_is_constant(expr) [MACRO] |
107 | =item bool ecb_is_constant(expr) |
67 | |
108 | |
68 | Returns true iff the expression can be deduced to be a compile-time |
109 | Returns true iff the expression can be deduced to be a compile-time |
69 | constant, and false otherwise. |
110 | constant, and false otherwise. |
70 | |
111 | |
71 | For example, when you have a C<rndm16> function that returns a 16 bit |
112 | For example, when you have a C<rndm16> function that returns a 16 bit |
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89 | return is_constant (n) && !(n & (n - 1)) |
130 | return is_constant (n) && !(n & (n - 1)) |
90 | ? rndm16 () & (num - 1) |
131 | ? rndm16 () & (num - 1) |
91 | : (n * (uint32_t)rndm16 ()) >> 16; |
132 | : (n * (uint32_t)rndm16 ()) >> 16; |
92 | } |
133 | } |
93 | |
134 | |
94 | =item bool ecb_expect (expr, value) [MACRO] |
135 | =item bool ecb_expect (expr, value) |
95 | |
136 | |
96 | Evaluates C<expr> and returns it. In addition, it tells the compiler that |
137 | Evaluates C<expr> and returns it. In addition, it tells the compiler that |
97 | the C<expr> evaluates to C<value> a lot, which can be used for static |
138 | the C<expr> evaluates to C<value> a lot, which can be used for static |
98 | branch optimisations. |
139 | branch optimisations. |
99 | |
140 | |
100 | Usually, you want to use the more intuitive C<ecb_likely> and |
141 | Usually, you want to use the more intuitive C<ecb_likely> and |
101 | C<ecb_unlikely> functions instead. |
142 | C<ecb_unlikely> functions instead. |
102 | |
143 | |
103 | =item bool ecb_likely (bool) [MACRO] |
144 | =item bool ecb_likely (bool) |
104 | |
145 | |
105 | =item bool ecb_unlikely (bool) [MACRO] |
146 | =item bool ecb_unlikely (bool) |
106 | |
147 | |
107 | These two functions expect a expression that is true or false and return |
148 | These two functions expect a expression that is true or false and return |
108 | C<1> or C<0>, respectively, so when used in the condition of an C<if> or |
149 | C<1> or C<0>, respectively, so when used in the condition of an C<if> or |
109 | other conditional statement, it will not change the program: |
150 | other conditional statement, it will not change the program: |
110 | |
151 | |
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140 | { |
181 | { |
141 | if (ecb_unlikely (current + size > end)) |
182 | if (ecb_unlikely (current + size > end)) |
142 | real_reserve_method (size); /* presumably noinline */ |
183 | real_reserve_method (size); /* presumably noinline */ |
143 | } |
184 | } |
144 | |
185 | |
145 | =item bool ecb_assume (cond) [MACRO] |
186 | =item bool ecb_assume (cond) |
146 | |
187 | |
147 | Try to tell the compiler that some condition is true, even if it's not |
188 | Try to tell the compiler that some condition is true, even if it's not |
148 | obvious. |
189 | obvious. |
149 | |
190 | |
150 | This can be used to teach the compiler about invariants or other |
191 | This can be used to teach the compiler about invariants or other |
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176 | |
217 | |
177 | This function does nothing itself, except tell the compiler that it will |
218 | This function does nothing itself, except tell the compiler that it will |
178 | never be executed. Apart from suppressing a warning in some cases, this |
219 | never be executed. Apart from suppressing a warning in some cases, this |
179 | function can be used to implement C<ecb_assume> or similar functions. |
220 | function can be used to implement C<ecb_assume> or similar functions. |
180 | |
221 | |
181 | =item bool ecb_prefetch (addr, rw, locality) [MACRO] |
222 | =item bool ecb_prefetch (addr, rw, locality) |
182 | |
223 | |
183 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
224 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
184 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
225 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
185 | C<0> means that there will only be one access later, C<3> means that |
226 | C<0> means that there will only be one access later, C<3> means that |
186 | the data will likely be accessed very often, and values in between mean |
227 | the data will likely be accessed very often, and values in between mean |
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248 | |
289 | |
249 | =item uint32_t ecb_bswap16 (uint32_t x) |
290 | =item uint32_t ecb_bswap16 (uint32_t x) |
250 | |
291 | |
251 | =item uint32_t ecb_bswap32 (uint32_t x) |
292 | =item uint32_t ecb_bswap32 (uint32_t x) |
252 | |
293 | |
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294 | These two functions return the value of the 16-bit (32-bit) variable |
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295 | C<x> after reversing the order of bytes. |
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296 | |
253 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
297 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
254 | |
298 | |
255 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
299 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
256 | |
300 | |
257 | These two functions return the value of C<x> after shifting all the bits |
301 | These two functions return the value of C<x> after shifting all the bits |
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261 | |
305 | |
262 | =head2 ARITHMETIC |
306 | =head2 ARITHMETIC |
263 | |
307 | |
264 | =over 4 |
308 | =over 4 |
265 | |
309 | |
266 | =item x = ecb_mod (m, n) [MACRO] |
310 | =item x = ecb_mod (m, n) |
267 | |
311 | |
268 | Returns the positive remainder of the modulo operation between C<m> |
312 | Returns the positive remainder of the modulo operation between C<m> and |
269 | and C<n>. |
313 | C<n>. Unlike the C moduloe operator C<%>, this function ensures that the |
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314 | return value is always positive). |
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315 | |
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316 | C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be |
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317 | negatable, that is, both C<m> and C<-m> must be representable in its |
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318 | type. |
270 | |
319 | |
271 | =back |
320 | =back |
272 | |
321 | |
273 | =head2 UTILITY |
322 | =head2 UTILITY |
274 | |
323 | |
275 | =over 4 |
324 | =over 4 |
276 | |
325 | |
277 | =item element_count = ecb_array_length (name) [MACRO] |
326 | =item element_count = ecb_array_length (name) [MACRO] |
278 | |
327 | |
279 | =back |
328 | Returns the number of elements in the array C<name>. For example: |
280 | |
329 | |
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330 | int primes[] = { 2, 3, 5, 7, 11 }; |
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331 | int sum = 0; |
281 | |
332 | |
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333 | for (i = 0; i < ecb_array_length (primes); i++) |
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334 | sum += primes [i]; |
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335 | |
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336 | =back |
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337 | |
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338 | |