[ViewVC] Diff of: cvs/libecb/ecb.pod

Comparing libecb/ecb.pod (file contents):
Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.82 by root, Mon Jan 20 21:02:28 2020 UTC

…		…
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around GCC built-ins, together
16	with replacement functions for other compilers. In addition to this,	16	with replacement functions for other compilers. In addition to this,
17	it provides a number of other lowlevel C utilities, such as endianness	17	it provides a number of other lowlevel C utilities, such as endianness
18	detection, byte swapping or bit rotations.	18	detection, byte swapping or bit rotations.
19		19
20	Or in other words, things that should be built-in into any standard C	20	Or in other words, things that should be built into any standard C system,
21	system, but aren't.	21	but aren't, implemented as efficient as possible with GCC, and still
		22	correct with other compilers.
22		23
23	More might come.	24	More might come.
24		25
25	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
26		27
…		…
53	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
54	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
55	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
56	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
57		58
		59	=head2 TYPES / TYPE SUPPORT
		60
		61	ecb.h makes sure that the following types are defined (in the expected way):
		62
		63	int8_t uint8_
		64	int16_t uint16_t
		65	int32_t uint32_
		66	int64_t uint64_t
		67	int_fast8_t uint_fast8_t
		68	int_fast16_t uint_fast16_t
		69	int_fast32_t uint_fast32_t
		70	int_fast64_t uint_fast64_t
		71	intptr_t uintptr_t
		72
		73	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
		74	platform (currently C<4> or C<8>) and can be used in preprocessor
		75	expressions.
		76
		77	For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>.
		78
		79	=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
		80
		81	All the following symbols expand to an expression that can be tested in
		82	preprocessor instructions as well as treated as a boolean (use C<!!> to
		83	ensure it's either C<0> or C<1> if you need that).
		84
		85	=over 4
		86
		87	=item ECB_C
		88
		89	True if the implementation defines the C<__STDC__> macro to a true value,
		90	while not claiming to be C++, i..e C, but not C++.
		91
		92	=item ECB_C99
		93
		94	True if the implementation claims to be compliant to C99 (ISO/IEC
		95	9899:1999) or any later version, while not claiming to be C++.
		96
		97	Note that later versions (ECB_C11) remove core features again (for
		98	example, variable length arrays).
		99
		100	=item ECB_C11, ECB_C17
		101
		102	True if the implementation claims to be compliant to C11/C17 (ISO/IEC
		103	9899:2011, :20187) or any later version, while not claiming to be C++.
		104
		105	=item ECB_CPP
		106
		107	True if the implementation defines the C<__cplusplus__> macro to a true
		108	value, which is typically true for C++ compilers.
		109
		110	=item ECB_CPP11, ECB_CPP14, ECB_CPP17
		111
		112	True if the implementation claims to be compliant to C++11/C++14/C++17
		113	(ISO/IEC 14882:2011, :2014, :2017) or any later version.
		114
		115	=item ECB_OPTIMIZE_SIZE
		116
		117	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
		118	can also be defined before including F<ecb.h>, in which case it will be
		119	unchanged.
		120
		121	=item ECB_GCC_VERSION (major, minor)
		122
		123	Expands to a true value (suitable for testing in by the preprocessor)
		124	if the compiler used is GNU C and the version is the given version, or
		125	higher.
		126
		127	This macro tries to return false on compilers that claim to be GCC
		128	compatible but aren't.
		129
		130	=item ECB_EXTERN_C
		131
		132	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		133
		134	This can be used to declare a single external C function:
		135
		136	ECB_EXTERN_C int printf (const char *format, ...);
		137
		138	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		139
		140	These two macros can be used to wrap multiple C<extern "C"> definitions -
		141	they expand to nothing in C.
		142
		143	They are most useful in header files:
		144
		145	ECB_EXTERN_C_BEG
		146
		147	int mycfun1 (int x);
		148	int mycfun2 (int x);
		149
		150	ECB_EXTERN_C_END
		151
		152	=item ECB_STDFP
		153
		154	If this evaluates to a true value (suitable for testing in by the
		155	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		156	and double/binary64 representations internally I<and> the endianness of
		157	both types match the endianness of C<uint32_t> and C<uint64_t>.
		158
		159	This means you can just copy the bits of a C<float> (or C<double>) to an
		160	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		161	without having to think about format or endianness.
		162
		163	This is true for basically all modern platforms, although F<ecb.h> might
		164	not be able to deduce this correctly everywhere and might err on the safe
		165	side.
		166
		167	=item ECB_AMD64, ECB_AMD64_X32
		168
		169	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		170	ABI, respectively, and undefined elsewhere.
		171
		172	The designers of the new X32 ABI for some inexplicable reason decided to
		173	make it look exactly like amd64, even though it's completely incompatible
		174	to that ABI, breaking about every piece of software that assumed that
		175	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		176	necessary.
		177
		178	=back
		179
		180	=head2 MACRO TRICKERY
		181
		182	=over 4
		183
		184	=item ECB_CONCAT (a, b)
		185
		186	Expands any macros in C<a> and C<b>, then concatenates the result to form
		187	a single token. This is mainly useful to form identifiers from components,
		188	e.g.:
		189
		190	#define S1 str
		191	#define S2 cpy
		192
		193	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		194
		195	=item ECB_STRINGIFY (arg)
		196
		197	Expands any macros in C<arg> and returns the stringified version of
		198	it. This is mainly useful to get the contents of a macro in string form,
		199	e.g.:
		200
		201	#define SQL_LIMIT 100
		202	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		203
		204	=item ECB_STRINGIFY_EXPR (expr)
		205
		206	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		207	is a valid expression. This is useful to catch typos or cases where the
		208	macro isn't available:
		209
		210	#include <errno.h>
		211
		212	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		213	ECB_STRINGIFY_EXPR (EDOM); // "33"
		214
		215	// now imagine we had a typo:
		216
		217	ECB_STRINGIFY (EDAM); // "EDAM"
		218	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		219
		220	=back
		221
58	=head2 GCC ATTRIBUTES	222	=head2 ATTRIBUTES
59		223
60	blabla where to put, what others	224	A major part of libecb deals with additional attributes that can be
		225	assigned to functions, variables and sometimes even types - much like
		226	C<const> or C<volatile> in C. They are implemented using either GCC
		227	attributes or other compiler/language specific features. Attributes
		228	declarations must be put before the whole declaration:
61		229
62	=over 4	230	ecb_const int mysqrt (int a);
		231	ecb_unused int i;
63		232
64	=item ecb_attribute ((attrs...))	233	=over 4
65
66	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
67	nothing on other compilers, so the effect is that only GCC sees these.
68
69	Example: use the C<deprecated> attribute on a function.
70
71	ecb_attribute((__deprecated__)) void
72	do_not_use_me_anymore (void);
73		234
74	=item ecb_unused	235	=item ecb_unused
75		236
76	Marks a function or a variable as "unused", which simply suppresses a	237	Marks a function or a variable as "unused", which simply suppresses a
77	warning by GCC when it detects it as unused. This is useful when you e.g.	238	warning by GCC when it detects it as unused. This is useful when you e.g.
78	declare a variable but do not always use it:	239	declare a variable but do not always use it:
79		240
80	{	241	{
81	int var ecb_unused;	242	ecb_unused int var;
82		243
83	#ifdef SOMECONDITION	244	#ifdef SOMECONDITION
84	var = ...;	245	var = ...;
85	return var;	246	return var;
86	#else	247	#else
87	return 0;	248	return 0;
88	#endif	249	#endif
89	}	250	}
90		251
		252	=item ecb_deprecated
		253
		254	Similar to C<ecb_unused>, but marks a function, variable or type as
		255	deprecated. This makes some compilers warn when the type is used.
		256
		257	=item ecb_deprecated_message (message)
		258
		259	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		260	used instead of a generic depreciation message when the object is being
		261	used.
		262
		263	=item ecb_inline
		264
		265	Expands either to (a compiler-specific equivalent of) C<static inline> or
		266	to just C<static>, if inline isn't supported. It should be used to declare
		267	functions that should be inlined, for code size or speed reasons.
		268
		269	Example: inline this function, it surely will reduce codesize.
		270
		271	ecb_inline int
		272	negmul (int a, int b)
		273	{
		274	return - (a * b);
		275	}
		276
91	=item ecb_noinline	277	=item ecb_noinline
92		278
93	Prevent a function from being inlined - it might be optimised away, but	279	Prevents a function from being inlined - it might be optimised away, but
94	not inlined into other functions. This is useful if you know your function	280	not inlined into other functions. This is useful if you know your function
95	is rarely called and large enough for inlining not to be helpful.	281	is rarely called and large enough for inlining not to be helpful.
96		282
97	=item ecb_noreturn	283	=item ecb_noreturn
98		284
…		…
105	{	291	{
106	puts (errline);	292	puts (errline);
107	abort ();	293	abort ();
108	}	294	}
109		295
110	In this case, the compiler would probbaly be smart enough to decude it on	296	In this case, the compiler would probably be smart enough to deduce it on
111	it's own, so this is mainly useful for declarations.	297	its own, so this is mainly useful for declarations.
		298
		299	=item ecb_restrict
		300
		301	Expands to the C<restrict> keyword or equivalent on compilers that support
		302	them, and to nothing on others. Must be specified on a pointer type or
		303	an array index to indicate that the memory doesn't alias with any other
		304	restricted pointer in the same scope.
		305
		306	Example: multiply a vector, and allow the compiler to parallelise the
		307	loop, because it knows it doesn't overwrite input values.
		308
		309	void
		310	multiply (ecb_restrict float *src,
		311	ecb_restrict float *dst,
		312	int len, float factor)
		313	{
		314	int i;
		315
		316	for (i = 0; i < len; ++i)
		317	dst [i] = src [i] * factor;
		318	}
112		319
113	=item ecb_const	320	=item ecb_const
114		321
115	Declares that the function only depends on the values of it's arguments,	322	Declares that the function only depends on the values of its arguments,
116	much like a mathematical function. It specifically does not read or write	323	much like a mathematical function. It specifically does not read or write
117	any memory any arguments might point to, global variables, or call any	324	any memory any arguments might point to, global variables, or call any
118	non-const functions. It also must not have any side effects.	325	non-const functions. It also must not have any side effects.
119		326
120	Such a function can be optimised much more aggressively by the compiler -	327	Such a function can be optimised much more aggressively by the compiler -
121	for example, multiple calls with the same arguments can be optimised into	328	for example, multiple calls with the same arguments can be optimised into
122	a single call, which wouldn't be possible if the compiler would have to	329	a single call, which wouldn't be possible if the compiler would have to
123	expect any side effects.	330	expect any side effects.
124		331
125	It is best suited for functions in the sense of mathematical functions,	332	It is best suited for functions in the sense of mathematical functions,
126	such as a function return the square root of its input argument.	333	such as a function returning the square root of its input argument.
127		334
128	Not suited would be a function that calculates the hash of some memory	335	Not suited would be a function that calculates the hash of some memory
129	area you pass in, prints some messages or looks at a global variable to	336	area you pass in, prints some messages or looks at a global variable to
130	decide on rounding.	337	decide on rounding.
131		338
…		…
154	possible.	361	possible.
155		362
156	The compiler reacts by trying to place hot functions near to each other in	363	The compiler reacts by trying to place hot functions near to each other in
157	memory.	364	memory.
158		365
159	Whether a function is hot or not often depend son the whole program,	366	Whether a function is hot or not often depends on the whole program,
160	and less on the function itself. C<ecb_cold> is likely more useful in	367	and less on the function itself. C<ecb_cold> is likely more useful in
161	practise.	368	practise.
162		369
163	=item ecb_cold	370	=item ecb_cold
164		371
…		…
169		376
170	In addition to placing cold functions together (or at least away from hot	377	In addition to placing cold functions together (or at least away from hot
171	functions), this knowledge can be used in other ways, for example, the	378	functions), this knowledge can be used in other ways, for example, the
172	function will be optimised for size, as opposed to speed, and codepaths	379	function will be optimised for size, as opposed to speed, and codepaths
173	leading to calls to those functions can automatically be marked as if	380	leading to calls to those functions can automatically be marked as if
174	C<ecb_unlikel> had been used to reach them.	381	C<ecb_expect_false> had been used to reach them.
175		382
176	Good examples for such functions would be error reporting functions, or	383	Good examples for such functions would be error reporting functions, or
177	functions only called in exceptional or rare cases.	384	functions only called in exceptional or rare cases.
178		385
179	=item ecb_artificial	386	=item ecb_artificial
180		387
181	Declares the function as "artificial", in this case meaning that this	388	Declares the function as "artificial", in this case meaning that this
182	function is not really mean to be a function, but more like an accessor	389	function is not really meant to be a function, but more like an accessor
183	- many methods in C++ classes are mere accessor functions, and having a	390	- many methods in C++ classes are mere accessor functions, and having a
184	crash reported in such a method, or single-stepping through them, is not	391	crash reported in such a method, or single-stepping through them, is not
185	usually so helpful, especially when it's inlined to just a few instructions.	392	usually so helpful, especially when it's inlined to just a few instructions.
186		393
187	Marking them as artificial will instruct the debugger about just this,	394	Marking them as artificial will instruct the debugger about just this,
…		…
207		414
208	=head2 OPTIMISATION HINTS	415	=head2 OPTIMISATION HINTS
209		416
210	=over 4	417	=over 4
211		418
212	=item bool ecb_is_constant(expr)	419	=item bool ecb_is_constant (expr)
213		420
214	Returns true iff the expression can be deduced to be a compile-time	421	Returns true iff the expression can be deduced to be a compile-time
215	constant, and false otherwise.	422	constant, and false otherwise.
216		423
217	For example, when you have a C<rndm16> function that returns a 16 bit	424	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
235	return is_constant (n) && !(n & (n - 1))	442	return is_constant (n) && !(n & (n - 1))
236	? rndm16 () & (num - 1)	443	? rndm16 () & (num - 1)
237	: (n * (uint32_t)rndm16 ()) >> 16;	444	: (n * (uint32_t)rndm16 ()) >> 16;
238	}	445	}
239		446
240	=item bool ecb_expect (expr, value)	447	=item ecb_expect (expr, value)
241		448
242	Evaluates C<expr> and returns it. In addition, it tells the compiler that	449	Evaluates C<expr> and returns it. In addition, it tells the compiler that
243	the C<expr> evaluates to C<value> a lot, which can be used for static	450	the C<expr> evaluates to C<value> a lot, which can be used for static
244	branch optimisations.	451	branch optimisations.
245		452
246	Usually, you want to use the more intuitive C<ecb_likely> and	453	Usually, you want to use the more intuitive C<ecb_expect_true> and
247	C<ecb_unlikely> functions instead.	454	C<ecb_expect_false> functions instead.
248		455
		456	=item bool ecb_expect_true (cond)
		457
249	=item bool ecb_likely (cond)	458	=item bool ecb_expect_false (cond)
250
251	=item bool ecb_unlikely (cond)
252		459
253	These two functions expect a expression that is true or false and return	460	These two functions expect a expression that is true or false and return
254	C<1> or C<0>, respectively, so when used in the condition of an C<if> or	461	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
255	other conditional statement, it will not change the program:	462	other conditional statement, it will not change the program:
256		463
257	/* these two do the same thing */	464	/* these two do the same thing */
258	if (some_condition) ...;	465	if (some_condition) ...;
259	if (ecb_likely (some_condition)) ...;	466	if (ecb_expect_true (some_condition)) ...;
260		467
261	However, by using C<ecb_likely>, you tell the compiler that the condition	468	However, by using C<ecb_expect_true>, you tell the compiler that the
262	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be	469	condition is likely to be true (and for C<ecb_expect_false>, that it is
263	true).	470	unlikely to be true).
264		471
265	For example, when you check for a null pointer and expect this to be a	472	For example, when you check for a null pointer and expect this to be a
266	rare, exceptional, case, then use C<ecb_unlikely>:	473	rare, exceptional, case, then use C<ecb_expect_false>:
267		474
268	void my_free (void *ptr)	475	void my_free (void *ptr)
269	{	476	{
270	if (ecb_unlikely (ptr == 0))	477	if (ecb_expect_false (ptr == 0))
271	return;	478	return;
272	}	479	}
273		480
274	Consequent use of these functions to mark away exceptional cases or to	481	Consequent use of these functions to mark away exceptional cases or to
275	tell the compiler what the hot path through a function is can increase	482	tell the compiler what the hot path through a function is can increase
276	performance considerably.	483	performance considerably.
		484
		485	You might know these functions under the name C<likely> and C<unlikely>
		486	- while these are common aliases, we find that the expect name is easier
		487	to understand when quickly skimming code. If you wish, you can use
		488	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		489	C<ecb_expect_false> - these are simply aliases.
277		490
278	A very good example is in a function that reserves more space for some	491	A very good example is in a function that reserves more space for some
279	memory block (for example, inside an implementation of a string stream) -	492	memory block (for example, inside an implementation of a string stream) -
280	each time something is added, you have to check for a buffer overrun, but	493	each time something is added, you have to check for a buffer overrun, but
281	you expect that most checks will turn out to be false:	494	you expect that most checks will turn out to be false:
282		495
283	/* make sure we have "size" extra room in our buffer */	496	/* make sure we have "size" extra room in our buffer */
284	ecb_inline void	497	ecb_inline void
285	reserve (int size)	498	reserve (int size)
286	{	499	{
287	if (ecb_unlikely (current + size > end))	500	if (ecb_expect_false (current + size > end))
288	real_reserve_method (size); /* presumably noinline */	501	real_reserve_method (size); /* presumably noinline */
289	}	502	}
290		503
291	=item bool ecb_assume (cond)	504	=item ecb_assume (cond)
292		505
293	Try to tell the compiler that some condition is true, even if it's not	506	Tries to tell the compiler that some condition is true, even if it's not
294	obvious.	507	obvious. This is not a function, but a statement: it cannot be used in
		508	another expression.
295		509
296	This can be used to teach the compiler about invariants or other	510	This can be used to teach the compiler about invariants or other
297	conditions that might improve code generation, but which are impossible to	511	conditions that might improve code generation, but which are impossible to
298	deduce form the code itself.	512	deduce form the code itself.
299		513
300	For example, the example reservation function from the C<ecb_unlikely>	514	For example, the example reservation function from the C<ecb_expect_false>
301	description could be written thus (only C<ecb_assume> was added):	515	description could be written thus (only C<ecb_assume> was added):
302		516
303	ecb_inline void	517	ecb_inline void
304	reserve (int size)	518	reserve (int size)
305	{	519	{
306	if (ecb_unlikely (current + size > end))	520	if (ecb_expect_false (current + size > end))
307	real_reserve_method (size); /* presumably noinline */	521	real_reserve_method (size); /* presumably noinline */
308		522
309	ecb_assume (current + size <= end);	523	ecb_assume (current + size <= end);
310	}	524	}
311		525
…		…
316		530
317	Then the compiler I<might> be able to optimise out the second call	531	Then the compiler I<might> be able to optimise out the second call
318	completely, as it knows that C<< current + 1 > end >> is false and the	532	completely, as it knows that C<< current + 1 > end >> is false and the
319	call will never be executed.	533	call will never be executed.
320		534
321	=item bool ecb_unreachable ()	535	=item ecb_unreachable ()
322		536
323	This function does nothing itself, except tell the compiler that it will	537	This function does nothing itself, except tell the compiler that it will
324	never be executed. Apart from suppressing a warning in some cases, this	538	never be executed. Apart from suppressing a warning in some cases, this
325	function can be used to implement C<ecb_assume> or similar functions.	539	function can be used to implement C<ecb_assume> or similar functionality.
326		540
327	=item bool ecb_prefetch (addr, rw, locality)	541	=item ecb_prefetch (addr, rw, locality)
328		542
329	Tells the compiler to try to prefetch memory at the given C<addr>ess	543	Tells the compiler to try to prefetch memory at the given C<addr>ess
330	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of	544	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
331	C<0> means that there will only be one access later, C<3> means that	545	C<0> means that there will only be one access later, C<3> means that
332	the data will likely be accessed very often, and values in between mean	546	the data will likely be accessed very often, and values in between mean
333	something... in between. The memory pointed to by the address does not	547	something... in between. The memory pointed to by the address does not
334	need to be accessible (it could be a null pointer for example), but C<rw>	548	need to be accessible (it could be a null pointer for example), but C<rw>
335	and C<locality> must be compile-time constants.	549	and C<locality> must be compile-time constants.
336		550
		551	This is a statement, not a function: you cannot use it as part of an
		552	expression.
		553
337	An obvious way to use this is to prefetch some data far away, in a big	554	An obvious way to use this is to prefetch some data far away, in a big
338	array you loop over. This prefetches memory some 128 array elements later,	555	array you loop over. This prefetches memory some 128 array elements later,
339	in the hope that it will be ready when the CPU arrives at that location.	556	in the hope that it will be ready when the CPU arrives at that location.
340		557
341	int sum = 0;	558	int sum = 0;
…		…
360	After processing the node, (part of) the next node might already be in	577	After processing the node, (part of) the next node might already be in
361	cache.	578	cache.
362		579
363	=back	580	=back
364		581
365	=head2 BIT FIDDLING / BITSTUFFS	582	=head2 BIT FIDDLING / BIT WIZARDRY
366		583
367	=over 4	584	=over 4
368		585
369	=item bool ecb_big_endian ()	586	=item bool ecb_big_endian ()
370		587
…		…
372		589
373	These two functions return true if the byte order is big endian	590	These two functions return true if the byte order is big endian
374	(most-significant byte first) or little endian (least-significant byte	591	(most-significant byte first) or little endian (least-significant byte
375	first) respectively.	592	first) respectively.
376		593
		594	On systems that are neither, their return values are unspecified.
		595
377	=item int ecb_ctz32 (uint32_t x)	596	=item int ecb_ctz32 (uint32_t x)
378		597
		598	=item int ecb_ctz64 (uint64_t x)
		599
		600	=item int ecb_ctz (T x) [C++]
		601
379	Returns the index of the least significant bit set in C<x> (or	602	Returns the index of the least significant bit set in C<x> (or
380	equivalently the number of bits set to 0 before the least significant	603	equivalently the number of bits set to 0 before the least significant bit
381	bit set), starting from 0. If C<x> is 0 the result is undefined. A	604	set), starting from 0. If C<x> is 0 the result is undefined.
382	common use case is to compute the integer binary logarithm, i.e.,	605
383	floor(log2(n)). For example:	606	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		607
		608	The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
		609	C<uint32_t> and C<uint64_t> types.
		610
		611	For example:
384		612
385	ecb_ctz32 (3) = 0	613	ecb_ctz32 (3) = 0
386	ecb_ctz32 (6) = 1	614	ecb_ctz32 (6) = 1
387		615
		616	=item bool ecb_is_pot32 (uint32_t x)
		617
		618	=item bool ecb_is_pot64 (uint32_t x)
		619
		620	=item bool ecb_is_pot (T x) [C++]
		621
		622	Returns true iff C<x> is a power of two or C<x == 0>.
		623
		624	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		625
		626	The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
		627	C<uint32_t> and C<uint64_t> types.
		628
		629	=item int ecb_ld32 (uint32_t x)
		630
		631	=item int ecb_ld64 (uint64_t x)
		632
		633	=item int ecb_ld64 (T x) [C++]
		634
		635	Returns the index of the most significant bit set in C<x>, or the number
		636	of digits the number requires in binary (so that C<< 2**ld <= x <
		637	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		638	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		639	example to see how many bits a certain number requires to be encoded.
		640
		641	This function is similar to the "count leading zero bits" function, except
		642	that that one returns how many zero bits are "in front" of the number (in
		643	the given data type), while C<ecb_ld> returns how many bits the number
		644	itself requires.
		645
		646	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		647
		648	The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
		649	C<uint32_t> and C<uint64_t> types.
		650
388	=item int ecb_popcount32 (uint32_t x)	651	=item int ecb_popcount32 (uint32_t x)
389		652
		653	=item int ecb_popcount64 (uint64_t x)
		654
		655	=item int ecb_popcount (T x) [C++]
		656
390	Returns the number of bits set to 1 in C<x>. For example:	657	Returns the number of bits set to 1 in C<x>.
		658
		659	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		660
		661	The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
		662	C<uint32_t> and C<uint64_t> types.
		663
		664	For example:
391		665
392	ecb_popcount32 (7) = 3	666	ecb_popcount32 (7) = 3
393	ecb_popcount32 (255) = 8	667	ecb_popcount32 (255) = 8
394		668
		669	=item uint8_t ecb_bitrev8 (uint8_t x)
		670
		671	=item uint16_t ecb_bitrev16 (uint16_t x)
		672
		673	=item uint32_t ecb_bitrev32 (uint32_t x)
		674
		675	=item T ecb_bitrev (T x) [C++]
		676
		677	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		678	and so on.
		679
		680	The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
		681
		682	Example:
		683
		684	ecb_bitrev8 (0xa7) = 0xea
		685	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		686
		687	=item T ecb_bitrev (T x) [C++]
		688
		689	Overloaded C++ bitrev function.
		690
		691	C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
		692
395	=item uint32_t ecb_bswap16 (uint32_t x)	693	=item uint32_t ecb_bswap16 (uint32_t x)
396		694
397	=item uint32_t ecb_bswap32 (uint32_t x)	695	=item uint32_t ecb_bswap32 (uint32_t x)
398		696
		697	=item uint64_t ecb_bswap64 (uint64_t x)
		698
		699	=item T ecb_bswap (T x)
		700
399	These two functions return the value of the 16-bit (32-bit) variable	701	These functions return the value of the 16-bit (32-bit, 64-bit) value
400	C<x> after reversing the order of bytes.	702	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		703	C<ecb_bswap32>).
		704
		705	The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
		706	C<uint32_t> and C<uint64_t> types.
		707
		708	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		709
		710	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		711
		712	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		713
		714	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		715
		716	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		717
		718	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
401		719
402	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	720	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
403		721
404	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	722	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
405		723
406	These two functions return the value of C<x> after shifting all the bits	724	These two families of functions return the value of C<x> after rotating
407	by C<count> positions to the right or left respectively.	725	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		726	(C<ecb_rotl>).
		727
		728	Current GCC versions understand these functions and usually compile them
		729	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		730	x86).
		731
		732	=item T ecb_rotl (T x, unsigned int count) [C++]
		733
		734	=item T ecb_rotr (T x, unsigned int count) [C++]
		735
		736	Overloaded C++ rotl/rotr functions.
		737
		738	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
408		739
409	=back	740	=back
410		741
		742	=head2 HOST ENDIANNESS CONVERSION
		743
		744	=over 4
		745
		746	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		747
		748	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		749
		750	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		751
		752	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		753
		754	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		755
		756	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		757
		758	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		759
		760	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		761	where C<be> and C<le> stand for big endian and little endian, respectively.
		762
		763	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		764
		765	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		766
		767	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		768
		769	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		770
		771	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		772
		773	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		774
		775	Like above, but converts I<from> host byte order to the specified
		776	endianness.
		777
		778	=back
		779
		780	In C++ the following additional template functions are supported:
		781
		782	=over 4
		783
		784	=item T ecb_be_to_host (T v)
		785
		786	=item T ecb_le_to_host (T v)
		787
		788	=item T ecb_host_to_be (T v)
		789
		790	=item T ecb_host_to_le (T v)
		791
		792	These functions work like their C counterparts, above, but use templates,
		793	which make them useful in generic code.
		794
		795	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		796	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		797	again can be useful in generic code).
		798
		799	=head2 UNALIGNED LOAD/STORE
		800
		801	These function load or store unaligned multi-byte values.
		802
		803	=over 4
		804
		805	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		806
		807	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		808
		809	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		810
		811	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		812	memory.
		813
		814	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		815
		816	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		817
		818	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		819
		820	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		821
		822	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		823
		824	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		825
		826	Like above, but additionally convert from big endian (C<be>) or little
		827	endian (C<le>) byte order to host byte order while doing so.
		828
		829	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		830
		831	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		832
		833	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		834
		835	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		836	memory.
		837
		838	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		839
		840	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		841
		842	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		843
		844	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		845
		846	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		847
		848	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		849
		850	Like above, but additionally convert from host byte order to big endian
		851	(C<be>) or little endian (C<le>) byte order while doing so.
		852
		853	=back
		854
		855	In C++ the following additional template functions are supported:
		856
		857	=over 4
		858
		859	=item T ecb_peek<T> (const void *ptr)
		860
		861	=item T ecb_peek_be<T> (const void *ptr)
		862
		863	=item T ecb_peek_le<T> (const void *ptr)
		864
		865	=item T ecb_peek_u<T> (const void *ptr)
		866
		867	=item T ecb_peek_be_u<T> (const void *ptr)
		868
		869	=item T ecb_peek_le_u<T> (const void *ptr)
		870
		871	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		872	32 or 64 bit value from memory, with optional conversion from big/little
		873	endian.
		874
		875	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		876
		877	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		878
		879	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		880
		881	Unlike their C counterparts, these functions support 8 bit quantities
		882	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		883	all of which hopefully makes them more useful in generic code.
		884
		885	=item ecb_poke (void *ptr, T v)
		886
		887	=item ecb_poke_be (void *ptr, T v)
		888
		889	=item ecb_poke_le (void *ptr, T v)
		890
		891	=item ecb_poke_u (void *ptr, T v)
		892
		893	=item ecb_poke_be_u (void *ptr, T v)
		894
		895	=item ecb_poke_le_u (void *ptr, T v)
		896
		897	Again, similarly to their C counterparts, these functions store an
		898	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		899	big/little endian.
		900
		901	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		902
		903	Unlike their C counterparts, these functions support 8 bit quantities
		904	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		905	all of which hopefully makes them more useful in generic code.
		906
		907	=back
		908
		909	=head2 FLOATING POINT FIDDLING
		910
		911	=over 4
		912
		913	=item ECB_INFINITY [-UECB_NO_LIBM]
		914
		915	Evaluates to positive infinity if supported by the platform, otherwise to
		916	a truly huge number.
		917
		918	=item ECB_NAN [-UECB_NO_LIBM]
		919
		920	Evaluates to a quiet NAN if supported by the platform, otherwise to
		921	C<ECB_INFINITY>.
		922
		923	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		924
		925	Same as C<ldexpf>, but always available.
		926
		927	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		928
		929	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		930
		931	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		932
		933	These functions each take an argument in the native C<float> or C<double>
		934	type and return the IEEE 754 bit representation of it (binary16/half,
		935	binary32/single or binary64/double precision).
		936
		937	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		938	will be the most significant bit, followed by exponent and mantissa.
		939
		940	This function should work even when the native floating point format isn't
		941	IEEE compliant, of course at a speed and code size penalty, and of course
		942	also within reasonable limits (it tries to convert NaNs, infinities and
		943	denormals, but will likely convert negative zero to positive zero).
		944
		945	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		946	be able to optimise away this function completely.
		947
		948	These functions can be helpful when serialising floats to the network - you
		949	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		950
		951	Another use for these functions is to manipulate floating point values
		952	directly.
		953
		954	Silly example: toggle the sign bit of a float.
		955
		956	/* On gcc-4.7 on amd64, */
		957	/* this results in a single add instruction to toggle the bit, and 4 extra */
		958	/* instructions to move the float value to an integer register and back. */
		959
		960	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		961
		962	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		963
		964	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		965
		966	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		967
		968	The reverse operation of the previous function - takes the bit
		969	representation of an IEEE binary16, binary32 or binary64 number (half,
		970	single or double precision) and converts it to the native C<float> or
		971	C<double> format.
		972
		973	This function should work even when the native floating point format isn't
		974	IEEE compliant, of course at a speed and code size penalty, and of course
		975	also within reasonable limits (it tries to convert normals and denormals,
		976	and might be lucky for infinities, and with extraordinary luck, also for
		977	negative zero).
		978
		979	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		980	be able to optimise away this function completely.
		981
		982	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		983
		984	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		985
		986	Convert a IEEE binary32/single precision to binary16/half format, and vice
		987	versa, handling all details (round-to-nearest-even, subnormals, infinity
		988	and NaNs) correctly.
		989
		990	These are functions are available under C<-DECB_NO_LIBM>, since
		991	they do not rely on the platform floating point format. The
		992	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		993	usually what you want.
		994
		995	=back
		996
411	=head2 ARITHMETIC	997	=head2 ARITHMETIC
412		998
413	=over 4	999	=over 4
414		1000
415	=item x = ecb_mod (m, n)	1001	=item x = ecb_mod (m, n)
416		1002
417	Returns the positive remainder of the modulo operation between C<m> and	1003	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1004	of the division operation between C<m> and C<n>, using floored
418	C<n>. Unlike the C modulo operator C<%>, this function ensures that the	1005	division. Unlike the C remainder operator C<%>, this function ensures that
419	return value is always positive).	1006	the return value is always positive and that the two numbers I<m> and
		1007	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1008	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1009	in the language.
420		1010
421	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	1011	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
422	negatable, that is, both C<m> and C<-m> must be representable in its	1012	negatable, that is, both C<m> and C<-m> must be representable in its
423	type.	1013	type (this typically excludes the minimum signed integer value, the same
		1014	limitation as for C</> and C<%> in C).
		1015
		1016	Current GCC versions compile this into an efficient branchless sequence on
		1017	almost all CPUs.
		1018
		1019	For example, when you want to rotate forward through the members of an
		1020	array for increasing C<m> (which might be negative), then you should use
		1021	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1022	change direction for negative values:
		1023
		1024	for (m = -100; m <= 100; ++m)
		1025	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1026
		1027	=item x = ecb_div_rd (val, div)
		1028
		1029	=item x = ecb_div_ru (val, div)
		1030
		1031	Returns C<val> divided by C<div> rounded down or up, respectively.
		1032	C<val> and C<div> must have integer types and C<div> must be strictly
		1033	positive. Note that these functions are implemented with macros in C
		1034	and with function templates in C++.
424		1035
425	=back	1036	=back
426		1037
427	=head2 UTILITY	1038	=head2 UTILITY
428		1039
429	=over 4	1040	=over 4
430		1041
431	=item element_count = ecb_array_length (name) [MACRO]	1042	=item element_count = ecb_array_length (name)
432		1043
433	Returns the number of elements in the array C<name>. For example:	1044	Returns the number of elements in the array C<name>. For example:
434		1045
435	int primes[] = { 2, 3, 5, 7, 11 };	1046	int primes[] = { 2, 3, 5, 7, 11 };
436	int sum = 0;	1047	int sum = 0;
…		…
438	for (i = 0; i < ecb_array_length (primes); i++)	1049	for (i = 0; i < ecb_array_length (primes); i++)
439	sum += primes [i];	1050	sum += primes [i];
440		1051
441	=back	1052	=back
442		1053
		1054	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
443		1055
		1056	These symbols need to be defined before including F<ecb.h> the first time.
		1057
		1058	=over 4
		1059
		1060	=item ECB_NO_THREADS
		1061
		1062	If F<ecb.h> is never used from multiple threads, then this symbol can
		1063	be defined, in which case memory fences (and similar constructs) are
		1064	completely removed, leading to more efficient code and fewer dependencies.
		1065
		1066	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1067
		1068	=item ECB_NO_SMP
		1069
		1070	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1071	multiple threads, but never concurrently (e.g. if the system the program
		1072	runs on has only a single CPU with a single core, no hyperthreading and so
		1073	on), then this symbol can be defined, leading to more efficient code and
		1074	fewer dependencies.
		1075
		1076	=item ECB_NO_LIBM
		1077
		1078	When defined to C<1>, do not export any functions that might introduce
		1079	dependencies on the math library (usually called F<-lm>) - these are
		1080	marked with [-UECB_NO_LIBM].
		1081
		1082	=back
		1083
		1084	=head1 UNDOCUMENTED FUNCTIONALITY
		1085
		1086	F<ecb.h> is full of undocumented functionality as well, some of which is
		1087	intended to be internal-use only, some of which we forgot to document, and
		1088	some of which we hide because we are not sure we will keep the interface
		1089	stable.
		1090
		1091	While you are welcome to rummage around and use whatever you find useful
		1092	(we can't stop you), keep in mind that we will change undocumented
		1093	functionality in incompatible ways without thinking twice, while we are
		1094	considerably more conservative with documented things.
		1095
		1096	=head1 AUTHORS
		1097
		1098	C<libecb> is designed and maintained by:
		1099
		1100	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1101	Marc Alexander Lehmann <schmorp@schmorp.de>
		1102
		1103

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Comparing libecb/ecb.pod (file contents): Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs. Revision 1.82 by root, Mon Jan 20 21:02:28 2020 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.82 by root, Mon Jan 20 21:02:28 2020 UTC