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

Comparing libecb/ecb.pod (file contents):
Revision 1.25 by root, Tue May 31 21:52:31 2011 UTC vs.
Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC

…		…
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
		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++.
		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
59	=head2 GCC ATTRIBUTES	222	=head2 ATTRIBUTES
60		223
61	A major part of libecb deals with GCC attributes. These are additional	224	A major part of libecb deals with additional attributes that can be
62	attributes that you cna assign to functions, variables and sometimes even	225	assigned to functions, variables and sometimes even types - much like
63	types - much like C<const> or C<volatile> in C.	226	C<const> or C<volatile> in C. They are implemented using either GCC
64		227	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 expeted places, the safest way is to put attribute
67	declarations before the whole declaration:	228	declarations must be put before the whole declaration:
68		229
69	ecb_const int mysqrt (int a);	230	ecb_const int mysqrt (int a);
70	ecb_unused int i;	231	ecb_unused int i;
71		232
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	233	=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		234
89	=item ecb_unused	235	=item ecb_unused
90		236
91	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
92	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.
93	declare a variable but do not always use it:	239	declare a variable but do not always use it:
94		240
95	{	241	{
96	int var ecb_unused;	242	ecb_unused int var;
97		243
98	#ifdef SOMECONDITION	244	#ifdef SOMECONDITION
99	var = ...;	245	var = ...;
100	return var;	246	return var;
101	#else	247	#else
102	return 0;	248	return 0;
103	#endif	249	#endif
104	}	250	}
105		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
106	=item ecb_noinline	277	=item ecb_noinline
107		278
108	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
109	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
110	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.
111		282
112	=item ecb_noreturn	283	=item ecb_noreturn
113		284
…		…
123	}	294	}
124		295
125	In this case, the compiler would probably be smart enough to deduce it on	296	In this case, the compiler would probably be smart enough to deduce it on
126	its own, so this is mainly useful for declarations.	297	its own, so this is mainly useful for declarations.
127		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	}
		319
128	=item ecb_const	320	=item ecb_const
129		321
130	Declares that the function only depends on the values of its arguments,	322	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	323	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	324	any memory any arguments might point to, global variables, or call any
…		…
184		376
185	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
186	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
187	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
188	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
189	C<ecb_unlikely> had been used to reach them.	381	C<ecb_expect_false> had been used to reach them.
190		382
191	Good examples for such functions would be error reporting functions, or	383	Good examples for such functions would be error reporting functions, or
192	functions only called in exceptional or rare cases.	384	functions only called in exceptional or rare cases.
193		385
194	=item ecb_artificial	386	=item ecb_artificial
195		387
196	Declares the function as "artificial", in this case meaning that this	388	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	389	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	390	- 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	391	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.	392	usually so helpful, especially when it's inlined to just a few instructions.
201		393
202	Marking them as artificial will instruct the debugger about just this,	394	Marking them as artificial will instruct the debugger about just this,
…		…
222		414
223	=head2 OPTIMISATION HINTS	415	=head2 OPTIMISATION HINTS
224		416
225	=over 4	417	=over 4
226		418
227	=item bool ecb_is_constant(expr)	419	=item bool ecb_is_constant (expr)
228		420
229	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
230	constant, and false otherwise.	422	constant, and false otherwise.
231		423
232	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
…		…
250	return is_constant (n) && !(n & (n - 1))	442	return is_constant (n) && !(n & (n - 1))
251	? rndm16 () & (num - 1)	443	? rndm16 () & (num - 1)
252	: (n * (uint32_t)rndm16 ()) >> 16;	444	: (n * (uint32_t)rndm16 ()) >> 16;
253	}	445	}
254		446
255	=item bool ecb_expect (expr, value)	447	=item ecb_expect (expr, value)
256		448
257	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
258	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
259	branch optimisations.	451	branch optimisations.
260		452
261	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
262	C<ecb_unlikely> functions instead.	454	C<ecb_expect_false> functions instead.
263		455
		456	=item bool ecb_expect_true (cond)
		457
264	=item bool ecb_likely (cond)	458	=item bool ecb_expect_false (cond)
265
266	=item bool ecb_unlikely (cond)
267		459
268	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
269	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
270	other conditional statement, it will not change the program:	462	other conditional statement, it will not change the program:
271		463
272	/* these two do the same thing */	464	/* these two do the same thing */
273	if (some_condition) ...;	465	if (some_condition) ...;
274	if (ecb_likely (some_condition)) ...;	466	if (ecb_expect_true (some_condition)) ...;
275		467
276	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
277	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
278	true).	470	unlikely to be true).
279		471
280	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
281	rare, exceptional, case, then use C<ecb_unlikely>:	473	rare, exceptional, case, then use C<ecb_expect_false>:
282		474
283	void my_free (void *ptr)	475	void my_free (void *ptr)
284	{	476	{
285	if (ecb_unlikely (ptr == 0))	477	if (ecb_expect_false (ptr == 0))
286	return;	478	return;
287	}	479	}
288		480
289	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
290	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
291	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.
292		490
293	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
294	memory block (for example, inside an implementation of a string stream) -	492	memory block (for example, inside an implementation of a string stream) -
295	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
296	you expect that most checks will turn out to be false:	494	you expect that most checks will turn out to be false:
297		495
298	/* make sure we have "size" extra room in our buffer */	496	/* make sure we have "size" extra room in our buffer */
299	ecb_inline void	497	ecb_inline void
300	reserve (int size)	498	reserve (int size)
301	{	499	{
302	if (ecb_unlikely (current + size > end))	500	if (ecb_expect_false (current + size > end))
303	real_reserve_method (size); /* presumably noinline */	501	real_reserve_method (size); /* presumably noinline */
304	}	502	}
305		503
306	=item bool ecb_assume (cond)	504	=item ecb_assume (cond)
307		505
308	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
309	obvious.	507	obvious. This is not a function, but a statement: it cannot be used in
		508	another expression.
310		509
311	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
312	conditions that might improve code generation, but which are impossible to	511	conditions that might improve code generation, but which are impossible to
313	deduce form the code itself.	512	deduce form the code itself.
314		513
315	For example, the example reservation function from the C<ecb_unlikely>	514	For example, the example reservation function from the C<ecb_expect_false>
316	description could be written thus (only C<ecb_assume> was added):	515	description could be written thus (only C<ecb_assume> was added):
317		516
318	ecb_inline void	517	ecb_inline void
319	reserve (int size)	518	reserve (int size)
320	{	519	{
321	if (ecb_unlikely (current + size > end))	520	if (ecb_expect_false (current + size > end))
322	real_reserve_method (size); /* presumably noinline */	521	real_reserve_method (size); /* presumably noinline */
323		522
324	ecb_assume (current + size <= end);	523	ecb_assume (current + size <= end);
325	}	524	}
326		525
…		…
331		530
332	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
333	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
334	call will never be executed.	533	call will never be executed.
335		534
336	=item bool ecb_unreachable ()	535	=item ecb_unreachable ()
337		536
338	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
339	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
340	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.
341		540
342	=item bool ecb_prefetch (addr, rw, locality)	541	=item ecb_prefetch (addr, rw, locality)
343		542
344	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
345	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
346	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
347	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
348	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
349	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>
350	and C<locality> must be compile-time constants.	549	and C<locality> must be compile-time constants.
351		550
		551	This is a statement, not a function: you cannot use it as part of an
		552	expression.
		553
352	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
353	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,
354	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.
355		557
356	int sum = 0;	558	int sum = 0;
…		…
375	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
376	cache.	578	cache.
377		579
378	=back	580	=back
379		581
380	=head2 BIT FIDDLING / BITSTUFFS	582	=head2 BIT FIDDLING / BIT WIZARDRY
381		583
382	=over 4	584	=over 4
383		585
384	=item bool ecb_big_endian ()	586	=item bool ecb_big_endian ()
385		587
…		…
391		593
392	On systems that are neither, their return values are unspecified.	594	On systems that are neither, their return values are unspecified.
393		595
394	=item int ecb_ctz32 (uint32_t x)	596	=item int ecb_ctz32 (uint32_t x)
395		597
		598	=item int ecb_ctz64 (uint64_t x)
		599
		600	=item int ecb_ctz (T x) [C++]
		601
396	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
397	equivalently the number of bits set to 0 before the least significant bit	603	equivalently the number of bits set to 0 before the least significant bit
398	set), starting from 0. If C<x> is 0 the result is undefined. A common use	604	set), starting from 0. If C<x> is 0 the result is undefined.
399	case is to compute the integer binary logarithm, i.e., C<floor (log2	605
		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
400	(n))>. For example:	611	For example:
401		612
402	ecb_ctz32 (3) = 0	613	ecb_ctz32 (3) = 0
403	ecb_ctz32 (6) = 1	614	ecb_ctz32 (6) = 1
404		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
405	=item int ecb_popcount32 (uint32_t x)	651	=item int ecb_popcount32 (uint32_t x)
406		652
		653	=item int ecb_popcount64 (uint64_t x)
		654
		655	=item int ecb_popcount (T x) [C++]
		656
407	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:
408		665
409	ecb_popcount32 (7) = 3	666	ecb_popcount32 (7) = 3
410	ecb_popcount32 (255) = 8	667	ecb_popcount32 (255) = 8
411		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
412	=item uint32_t ecb_bswap16 (uint32_t x)	693	=item uint32_t ecb_bswap16 (uint32_t x)
413		694
414	=item uint32_t ecb_bswap32 (uint32_t x)	695	=item uint32_t ecb_bswap32 (uint32_t x)
415		696
		697	=item uint64_t ecb_bswap64 (uint64_t x)
		698
		699	=item T ecb_bswap (T x)
		700
416	These two functions return the value of the 16-bit (32-bit) value C<x>	701	These functions return the value of the 16-bit (32-bit, 64-bit) value
417	after reversing the order of bytes (0x11223344 becomes 0x44332211).	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)
418		719
419	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	720	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
420		721
421	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	722	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
422		723
423	These two functions return the value of C<x> after rotating all the bits	724	These two families of functions return the value of C<x> after rotating
424	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>).
425		727
426	Current GCC versions understand these functions and usually compile them	728	Current GCC versions understand these functions and usually compile them
427	to "optimal" code (e.g. a single C<roll> on x86).	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>.
		739
		740	=back
		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.
428		994
429	=back	995	=back
430		996
431	=head2 ARITHMETIC	997	=head2 ARITHMETIC
432		998
…		…
442	C<ecb_mod> implements the mathematical modulo operation, which is missing	1008	C<ecb_mod> implements the mathematical modulo operation, which is missing
443	in the language.	1009	in the language.
444		1010
445	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
446	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
447	type (this typically includes the minimum signed integer value, the same	1013	type (this typically excludes the minimum signed integer value, the same
448	limitation as for C</> and C<%> in C).	1014	limitation as for C</> and C<%> in C).
449		1015
450	Current GCC versions compile this into an efficient branchless sequence on	1016	Current GCC versions compile this into an efficient branchless sequence on
451	many systems.	1017	almost all CPUs.
452		1018
453	For example, when you want to rotate forward through the members of an	1019	For example, when you want to rotate forward through the members of an
454	array for increasing C<m> (which might be negative), then you should use	1020	array for increasing C<m> (which might be negative), then you should use
455	C<ecb_mod>, as the C<%> operator might give either negative results, or	1021	C<ecb_mod>, as the C<%> operator might give either negative results, or
456	change direction for negative values:	1022	change direction for negative values:
457		1023
458	for (m = -100; m <= 100; ++m)	1024	for (m = -100; m <= 100; ++m)
459	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];	1025	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
460		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++.
		1035
461	=back	1036	=back
462		1037
463	=head2 UTILITY	1038	=head2 UTILITY
464		1039
465	=over 4	1040	=over 4
…		…
474	for (i = 0; i < ecb_array_length (primes); i++)	1049	for (i = 0; i < ecb_array_length (primes); i++)
475	sum += primes [i];	1050	sum += primes [i];
476		1051
477	=back	1052	=back
478		1053
		1054	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
479		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 1.25 by root, Tue May 31 21:52:31 2011 UTC vs. Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.25 by root, Tue May 31 21:52:31 2011 UTC vs.
Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC