… | |
… | |
68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
69 | expressions. |
69 | expressions. |
70 | |
70 | |
71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
72 | |
72 | |
73 | =head2 LANGUAGE/COMPILER VERSIONS |
73 | =head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS |
74 | |
74 | |
75 | All the following symbols expand to an expression that can be tested in |
75 | All the following symbols expand to an expression that can be tested in |
76 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
76 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
77 | ensure it's either C<0> or C<1> if you need that). |
77 | ensure it's either C<0> or C<1> if you need that). |
78 | |
78 | |
… | |
… | |
163 | C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
163 | C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
164 | necessary. |
164 | necessary. |
165 | |
165 | |
166 | =back |
166 | =back |
167 | |
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 | |
168 | =head2 GCC ATTRIBUTES |
210 | =head2 ATTRIBUTES |
169 | |
211 | |
170 | 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 |
171 | attributes that you can assign to functions, variables and sometimes even |
213 | assigned to functions, variables and sometimes even types - much like |
172 | types - much like C<const> or C<volatile> in C. |
214 | C<const> or C<volatile> in C. They are implemented using either GCC |
173 | |
215 | attributes or other compiler/language specific features. Attributes |
174 | While GCC allows declarations to show up in many surprising places, |
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175 | but not in many expected places, the safest way is to put attribute |
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176 | declarations before the whole declaration: |
216 | declarations must be put before the whole declaration: |
177 | |
217 | |
178 | ecb_const int mysqrt (int a); |
218 | ecb_const int mysqrt (int a); |
179 | ecb_unused int i; |
219 | ecb_unused int i; |
180 | |
220 | |
181 | For variables, it is often nicer to put the attribute after the name, and |
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182 | avoid multiple declarations using commas: |
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183 | |
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184 | int i ecb_unused; |
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185 | |
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186 | =over 4 |
221 | =over 4 |
187 | |
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188 | =item ecb_attribute ((attrs...)) |
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189 | |
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190 | A simple wrapper that expands to C<__attribute__((attrs))> on GCC 3.1+ and |
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191 | Clang 2.8+, and to nothing on other compilers, so the effect is that only |
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192 | GCC and Clang see these. |
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193 | |
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194 | Example: use the C<deprecated> attribute on a function. |
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195 | |
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196 | ecb_attribute((__deprecated__)) void |
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197 | do_not_use_me_anymore (void); |
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198 | |
222 | |
199 | =item ecb_unused |
223 | =item ecb_unused |
200 | |
224 | |
201 | 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 |
202 | 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. |
203 | declare a variable but do not always use it: |
227 | declare a variable but do not always use it: |
204 | |
228 | |
205 | { |
229 | { |
206 | int var ecb_unused; |
230 | ecb_unused int var; |
207 | |
231 | |
208 | #ifdef SOMECONDITION |
232 | #ifdef SOMECONDITION |
209 | var = ...; |
233 | var = ...; |
210 | return var; |
234 | return var; |
211 | #else |
235 | #else |
… | |
… | |
216 | =item ecb_deprecated |
240 | =item ecb_deprecated |
217 | |
241 | |
218 | Similar to C<ecb_unused>, but marks a function, variable or type as |
242 | Similar to C<ecb_unused>, but marks a function, variable or type as |
219 | deprecated. This makes some compilers warn when the type is used. |
243 | deprecated. This makes some compilers warn when the type is used. |
220 | |
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, the specified diagnostic 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 | |
221 | =item ecb_inline |
251 | =item ecb_inline |
222 | |
252 | |
223 | This is not actually an attribute, but you use it like one. It expands |
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224 | 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 |
225 | 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 |
226 | for code size or speed reasons. |
255 | inlined, for code size or speed reasons. |
227 | |
256 | |
228 | Example: inline this function, it surely will reduce codesize. |
257 | Example: inline this function, it surely will reduce codesize. |
229 | |
258 | |
230 | ecb_inline int |
259 | ecb_inline int |
231 | negmul (int a, int b) |
260 | negmul (int a, int b) |
… | |
… | |
233 | return - (a * b); |
262 | return - (a * b); |
234 | } |
263 | } |
235 | |
264 | |
236 | =item ecb_noinline |
265 | =item ecb_noinline |
237 | |
266 | |
238 | 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 |
239 | 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 |
240 | 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. |
241 | |
270 | |
242 | =item ecb_noreturn |
271 | =item ecb_noreturn |
243 | |
272 | |
… | |
… | |
264 | |
293 | |
265 | Example: multiply a vector, and allow the compiler to parallelise the |
294 | Example: multiply a vector, and allow the compiler to parallelise the |
266 | loop, because it knows it doesn't overwrite input values. |
295 | loop, because it knows it doesn't overwrite input values. |
267 | |
296 | |
268 | void |
297 | void |
269 | multiply (float *ecb_restrict src, |
298 | multiply (ecb_restrict float *src, |
270 | float *ecb_restrict dst, |
299 | ecb_restrict float *dst, |
271 | int len, float factor) |
300 | int len, float factor) |
272 | { |
301 | { |
273 | int i; |
302 | int i; |
274 | |
303 | |
275 | for (i = 0; i < len; ++i) |
304 | for (i = 0; i < len; ++i) |
… | |
… | |
373 | |
402 | |
374 | =head2 OPTIMISATION HINTS |
403 | =head2 OPTIMISATION HINTS |
375 | |
404 | |
376 | =over 4 |
405 | =over 4 |
377 | |
406 | |
378 | =item bool ecb_is_constant(expr) |
407 | =item bool ecb_is_constant (expr) |
379 | |
408 | |
380 | 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 |
381 | constant, and false otherwise. |
410 | constant, and false otherwise. |
382 | |
411 | |
383 | 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 |
… | |
… | |
401 | return is_constant (n) && !(n & (n - 1)) |
430 | return is_constant (n) && !(n & (n - 1)) |
402 | ? rndm16 () & (num - 1) |
431 | ? rndm16 () & (num - 1) |
403 | : (n * (uint32_t)rndm16 ()) >> 16; |
432 | : (n * (uint32_t)rndm16 ()) >> 16; |
404 | } |
433 | } |
405 | |
434 | |
406 | =item bool ecb_expect (expr, value) |
435 | =item ecb_expect (expr, value) |
407 | |
436 | |
408 | 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 |
409 | 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 |
410 | branch optimisations. |
439 | branch optimisations. |
411 | |
440 | |
… | |
… | |
458 | { |
487 | { |
459 | if (ecb_expect_false (current + size > end)) |
488 | if (ecb_expect_false (current + size > end)) |
460 | real_reserve_method (size); /* presumably noinline */ |
489 | real_reserve_method (size); /* presumably noinline */ |
461 | } |
490 | } |
462 | |
491 | |
463 | =item bool ecb_assume (cond) |
492 | =item ecb_assume (cond) |
464 | |
493 | |
465 | 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 |
466 | obvious. |
495 | obvious. This is not a function, but a statement: it cannot be used in |
|
|
496 | another expression. |
467 | |
497 | |
468 | 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 |
469 | conditions that might improve code generation, but which are impossible to |
499 | conditions that might improve code generation, but which are impossible to |
470 | deduce form the code itself. |
500 | deduce form the code itself. |
471 | |
501 | |
… | |
… | |
488 | |
518 | |
489 | 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 |
490 | 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 |
491 | call will never be executed. |
521 | call will never be executed. |
492 | |
522 | |
493 | =item bool ecb_unreachable () |
523 | =item ecb_unreachable () |
494 | |
524 | |
495 | 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 |
496 | 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 |
497 | 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. |
498 | |
528 | |
499 | =item bool ecb_prefetch (addr, rw, locality) |
529 | =item ecb_prefetch (addr, rw, locality) |
500 | |
530 | |
501 | 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 |
502 | 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 |
503 | 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 |
504 | 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 |
505 | 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 |
506 | 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> |
507 | and C<locality> must be compile-time constants. |
537 | and C<locality> must be compile-time constants. |
508 | |
538 | |
|
|
539 | This is a statement, not a function: you cannot use it as part of an |
|
|
540 | expression. |
|
|
541 | |
509 | 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 |
510 | 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, |
511 | 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. |
512 | |
545 | |
513 | int sum = 0; |
546 | int sum = 0; |
… | |
… | |
565 | |
598 | |
566 | =item bool ecb_is_pot32 (uint32_t x) |
599 | =item bool ecb_is_pot32 (uint32_t x) |
567 | |
600 | |
568 | =item bool ecb_is_pot64 (uint32_t x) |
601 | =item bool ecb_is_pot64 (uint32_t x) |
569 | |
602 | |
570 | 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>. |
571 | |
604 | |
572 | 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>. |
573 | |
606 | |
574 | =item int ecb_ld32 (uint32_t x) |
607 | =item int ecb_ld32 (uint32_t x) |
575 | |
608 | |
576 | =item int ecb_ld64 (uint64_t x) |
609 | =item int ecb_ld64 (uint64_t x) |
577 | |
610 | |
… | |
… | |
653 | |
686 | |
654 | =head2 FLOATING POINT FIDDLING |
687 | =head2 FLOATING POINT FIDDLING |
655 | |
688 | |
656 | =over 4 |
689 | =over 4 |
657 | |
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 | |
658 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
705 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
659 | |
706 | |
660 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
707 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
661 | |
708 | |
662 | These functions each take an argument in the native C<float> or C<double> |
709 | These functions each take an argument in the native C<float> or C<double> |
… | |
… | |
685 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
732 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
686 | /* instructions to move the float value to an integer register and back. */ |
733 | /* instructions to move the float value to an integer register and back. */ |
687 | |
734 | |
688 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
735 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
689 | |
736 | |
|
|
737 | =item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] |
|
|
738 | |
690 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
739 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
691 | |
740 | |
692 | =item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] |
741 | =item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM] |
693 | |
742 | |
694 | The reverse operation of the previos function - takes the bit representation |
743 | The reverse operation of the previous function - takes the bit |
695 | of an IEEE binary32 or binary64 number and converts it to the native C<float> |
744 | representation of an IEEE binary16, binary32 or binary64 number and |
696 | or C<double> format. |
745 | converts it to the native C<float> or C<double> format. |
697 | |
746 | |
698 | This function should work even when the native floating point format isn't |
747 | This function should work even when the native floating point format isn't |
699 | IEEE compliant, of course at a speed and code size penalty, and of course |
748 | IEEE compliant, of course at a speed and code size penalty, and of course |
700 | also within reasonable limits (it tries to convert normals and denormals, |
749 | also within reasonable limits (it tries to convert normals and denormals, |
701 | and might be lucky for infinities, and with extraordinary luck, also for |
750 | and might be lucky for infinities, and with extraordinary luck, also for |
… | |
… | |
791 | dependencies on the math library (usually called F<-lm>) - these are |
840 | dependencies on the math library (usually called F<-lm>) - these are |
792 | marked with [-UECB_NO_LIBM]. |
841 | marked with [-UECB_NO_LIBM]. |
793 | |
842 | |
794 | =back |
843 | =back |
795 | |
844 | |
|
|
845 | =head1 UNDOCUMENTED FUNCTIONALITY |
796 | |
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 | |