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		1	=head1 LIBECB - e-C-Builtins
1		2
		3	=head2 ABOUT LIBECB
		4
		5	Libecb is currently a simple header file that doesn't require any
		6	configuration to use or include in your project.
		7
		8	It's part of the e-suite of libraries, other members of which include
		9	libev and libeio.
		10
		11	Its homepage can be found here:
		12
		13	http://software.schmorp.de/pkg/libecb
		14
		15	It mainly provides a number of wrappers around many compiler built-ins,
		16	together with replacement functions for other compilers. In addition
		17	to this, it provides a number of other lowlevel C utilities, such as
		18	endianness detection, byte swapping or bit rotations.
		19
		20	Or in other words, things that should be built into any standard C
		21	system, but aren't, implemented as efficient as possible with GCC (clang,
		22	msvc...), and still correct with other compilers.
		23
		24	More might come.
		25
		26	=head2 ABOUT THE HEADER
		27
		28	At the moment, all you have to do is copy F<ecb.h> somewhere where your
		29	compiler can find it and include it:
		30
		31	#include <ecb.h>
		32
		33	The header should work fine for both C and C++ compilation, and gives you
		34	all of F<inttypes.h> in addition to the ECB symbols.
		35
		36	There are currently no object files to link to - future versions might
		37	come with an (optional) object code library to link against, to reduce
		38	code size or gain access to additional features.
		39
		40	It also currently includes everything from F<inttypes.h>.
		41
		42	=head2 ABOUT THIS MANUAL / CONVENTIONS
		43
		44	This manual mainly describes each (public) function available after
		45	including the F<ecb.h> header. The header might define other symbols than
		46	these, but these are not part of the public API, and not supported in any
		47	way.
		48
		49	When the manual mentions a "function" then this could be defined either as
		50	as inline function, a macro, or an external symbol.
		51
		52	When functions use a concrete standard type, such as C<int> or
		53	C<uint32_t>, then the corresponding function works only with that type. If
		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
		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.
		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
		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	Note that many C++20 features will likely have their own feature test
		116	macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>).
		117
		118	=item ECB_OPTIMIZE_SIZE
		119
		120	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
		121	can also be defined before including F<ecb.h>, in which case it will be
		122	unchanged.
		123
		124	=item ECB_GCC_VERSION (major, minor)
		125
		126	Expands to a true value (suitable for testing by the preprocessor) if the
		127	compiler used is GNU C and the version is the given version, or higher.
		128
		129	This macro tries to return false on compilers that claim to be GCC
		130	compatible but aren't.
		131
		132	=item ECB_EXTERN_C
		133
		134	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		135
		136	This can be used to declare a single external C function:
		137
		138	ECB_EXTERN_C int printf (const char *format, ...);
		139
		140	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		141
		142	These two macros can be used to wrap multiple C<extern "C"> definitions -
		143	they expand to nothing in C.
		144
		145	They are most useful in header files:
		146
		147	ECB_EXTERN_C_BEG
		148
		149	int mycfun1 (int x);
		150	int mycfun2 (int x);
		151
		152	ECB_EXTERN_C_END
		153
		154	=item ECB_STDFP
		155
		156	If this evaluates to a true value (suitable for testing by the
		157	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		158	and double/binary64 representations internally I<and> the endianness of
		159	both types match the endianness of C<uint32_t> and C<uint64_t>.
		160
		161	This means you can just copy the bits of a C<float> (or C<double>) to an
		162	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		163	without having to think about format or endianness.
		164
		165	This is true for basically all modern platforms, although F<ecb.h> might
		166	not be able to deduce this correctly everywhere and might err on the safe
		167	side.
		168
		169	=item ECB_64BIT_NATIVE
		170
		171	Evaluates to a true value (suitable for both preprocessor and C code
		172	testing) if 64 bit integer types on this architecture are evaluated
		173	"natively", that is, with similar speeds as 32 bit integerss. While 64 bit
		174	integer support is very common (and in fatc required by libecb), 32 bit
		175	cpus have to emulate operations on them, so you might want to avoid them.
		176
		177	=item ECB_AMD64, ECB_AMD64_X32
		178
		179	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		180	ABI, respectively, and undefined elsewhere.
		181
		182	The designers of the new X32 ABI for some inexplicable reason decided to
		183	make it look exactly like amd64, even though it's completely incompatible
		184	to that ABI, breaking about every piece of software that assumed that
		185	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		186	necessary.
		187
		188	=back
		189
		190	=head2 MACRO TRICKERY
		191
		192	=over
		193
		194	=item ECB_CONCAT (a, b)
		195
		196	Expands any macros in C<a> and C<b>, then concatenates the result to form
		197	a single token. This is mainly useful to form identifiers from components,
		198	e.g.:
		199
		200	#define S1 str
		201	#define S2 cpy
		202
		203	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		204
		205	=item ECB_STRINGIFY (arg)
		206
		207	Expands any macros in C<arg> and returns the stringified version of
		208	it. This is mainly useful to get the contents of a macro in string form,
		209	e.g.:
		210
		211	#define SQL_LIMIT 100
		212	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		213
		214	=item ECB_STRINGIFY_EXPR (expr)
		215
		216	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		217	is a valid expression. This is useful to catch typos or cases where the
		218	macro isn't available:
		219
		220	#include <errno.h>
		221
		222	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		223	ECB_STRINGIFY_EXPR (EDOM); // "33"
		224
		225	// now imagine we had a typo:
		226
		227	ECB_STRINGIFY (EDAM); // "EDAM"
		228	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		229
		230	=back
		231
2	=head2 GCC ATTRIBUTES	232	=head2 ATTRIBUTES
3		233
		234	A major part of libecb deals with additional attributes that can be
		235	assigned to functions, variables and sometimes even types - much like
		236	C<const> or C<volatile> in C. They are implemented using either GCC
		237	attributes or other compiler/language specific features. Attributes
		238	declarations must be put before the whole declaration:
		239
		240	ecb_const int mysqrt (int a);
		241	ecb_unused int i;
		242
4	=over 4	243	=over
5		244
6	=item ecb_attribute(attrlist)	245	=item ecb_unused
7	=item ecb_noinline ecb_attribute ((noinline))
8	=item ecb_noreturn ecb_attribute ((noreturn))
9	=item ecb_unused ecb_attribute ((unused))
10	=item ecb_const ecb_attribute ((const))
11	=item ecb_pure ecb_attribute ((pure))
12	=item ecb_hot ecb_attribute ((hot)) /* 4.3 */
13	=item ecb_cold ecb_attribute ((cold)) /* 4.3 */
14		246
		247	Marks a function or a variable as "unused", which simply suppresses a
		248	warning by the compiler when it detects it as unused. This is useful when
		249	you e.g. declare a variable but do not always use it:
		250
		251	{
		252	ecb_unused int var;
		253
		254	#ifdef SOMECONDITION
		255	var = ...;
		256	return var;
		257	#else
		258	return 0;
		259	#endif
		260	}
		261
		262	=item ecb_deprecated
		263
		264	Similar to C<ecb_unused>, but marks a function, variable or type as
		265	deprecated. This makes some compilers warn when the type is used.
		266
		267	=item ecb_deprecated_message (message)
		268
		269	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		270	used instead of a generic depreciation message when the object is being
		271	used.
		272
		273	=item ecb_inline
		274
		275	Expands either to (a compiler-specific equivalent of) C<static inline> or
		276	to just C<static>, if inline isn't supported. It should be used to declare
		277	functions that should be inlined, for code size or speed reasons.
		278
		279	Example: inline this function, it surely will reduce codesize.
		280
		281	ecb_inline int
		282	negmul (int a, int b)
		283	{
		284	return - (a * b);
		285	}
		286
		287	=item ecb_noinline
		288
		289	Prevents a function from being inlined - it might be optimised away, but
		290	not inlined into other functions. This is useful if you know your function
		291	is rarely called and large enough for inlining not to be helpful.
		292
		293	=item ecb_noreturn
		294
		295	Marks a function as "not returning, ever". Some typical functions that
		296	don't return are C<exit> or C<abort> (which really works hard to not
		297	return), and now you can make your own:
		298
		299	ecb_noreturn void
		300	my_abort (const char *errline)
		301	{
		302	puts (errline);
		303	abort ();
		304	}
		305
		306	In this case, the compiler would probably be smart enough to deduce it on
		307	its own, so this is mainly useful for declarations.
		308
		309	=item ecb_restrict
		310
		311	Expands to the C<restrict> keyword or equivalent on compilers that support
		312	them, and to nothing on others. Must be specified on a pointer type or
		313	an array index to indicate that the memory doesn't alias with any other
		314	restricted pointer in the same scope.
		315
		316	Example: multiply a vector, and allow the compiler to parallelise the
		317	loop, because it knows it doesn't overwrite input values.
		318
		319	void
		320	multiply (ecb_restrict float *src,
		321	ecb_restrict float *dst,
		322	int len, float factor)
		323	{
		324	int i;
		325
		326	for (i = 0; i < len; ++i)
		327	dst [i] = src [i] * factor;
		328	}
		329
		330	=item ecb_const
		331
		332	Declares that the function only depends on the values of its arguments,
		333	much like a mathematical function. It specifically does not read or write
		334	any memory any arguments might point to, global variables, or call any
		335	non-const functions. It also must not have any side effects.
		336
		337	Such a function can be optimised much more aggressively by the compiler -
		338	for example, multiple calls with the same arguments can be optimised into
		339	a single call, which wouldn't be possible if the compiler would have to
		340	expect any side effects.
		341
		342	It is best suited for functions in the sense of mathematical functions,
		343	such as a function returning the square root of its input argument.
		344
		345	Not suited would be a function that calculates the hash of some memory
		346	area you pass in, prints some messages or looks at a global variable to
		347	decide on rounding.
		348
		349	See C<ecb_pure> for a slightly less restrictive class of functions.
		350
		351	=item ecb_pure
		352
		353	Similar to C<ecb_const>, declares a function that has no side
		354	effects. Unlike C<ecb_const>, the function is allowed to examine global
		355	variables and any other memory areas (such as the ones passed to it via
		356	pointers).
		357
		358	While these functions cannot be optimised as aggressively as C<ecb_const>
		359	functions, they can still be optimised away in many occasions, and the
		360	compiler has more freedom in moving calls to them around.
		361
		362	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		363	function that calculates the MD5 sum of some input and updates some MD5
		364	state passed as argument would I<NOT> be pure, however, as it would modify
		365	some memory area that is not the return value.
		366
		367	=item ecb_hot
		368
		369	This declares a function as "hot" with regards to the cache - the function
		370	is used so often, that it is very beneficial to keep it in the cache if
		371	possible.
		372
		373	The compiler reacts by trying to place hot functions near to each other in
		374	memory.
		375
		376	Whether a function is hot or not often depends on the whole program,
		377	and less on the function itself. C<ecb_cold> is likely more useful in
		378	practise.
		379
		380	=item ecb_cold
		381
		382	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		383	the cache, or in other words, this function is not called often, or not at
		384	speed-critical times, and keeping it in the cache might be a waste of said
		385	cache.
		386
		387	In addition to placing cold functions together (or at least away from hot
		388	functions), this knowledge can be used in other ways, for example, the
		389	function will be optimised for size, as opposed to speed, and codepaths
		390	leading to calls to those functions can automatically be marked as if
		391	C<ecb_expect_false> had been used to reach them.
		392
		393	Good examples for such functions would be error reporting functions, or
		394	functions only called in exceptional or rare cases.
		395
		396	=item ecb_artificial
		397
		398	Declares the function as "artificial", in this case meaning that this
		399	function is not really meant to be a function, but more like an accessor
		400	- many methods in C++ classes are mere accessor functions, and having a
		401	crash reported in such a method, or single-stepping through them, is not
		402	usually so helpful, especially when it's inlined to just a few instructions.
		403
		404	Marking them as artificial will instruct the debugger about just this,
		405	leading to happier debugging and thus happier lives.
		406
		407	Example: in some kind of smart-pointer class, mark the pointer accessor as
		408	artificial, so that the whole class acts more like a pointer and less like
		409	some C++ abstraction monster.
		410
		411	template<typename T>
		412	struct my_smart_ptr
		413	{
		414	T *value;
		415
		416	ecb_artificial
		417	operator T *()
		418	{
		419	return value;
		420	}
		421	};
		422
15	=back	423	=back
16		424
17	=head2 OPTIMISATION HINTS	425	=head2 OPTIMISATION HINTS
18		426
19	=over 4	427	=over
20		428
21	=item bool ecb_is_constant(expr)	429	=item bool ecb_is_constant (expr)
22		430
		431	Returns true iff the expression can be deduced to be a compile-time
		432	constant, and false otherwise.
		433
		434	For example, when you have a C<rndm16> function that returns a 16 bit
		435	random number, and you have a function that maps this to a range from
		436	0..n-1, then you could use this inline function in a header file:
		437
		438	ecb_inline uint32_t
		439	rndm (uint32_t n)
		440	{
		441	return (n * (uint32_t)rndm16 ()) >> 16;
		442	}
		443
		444	However, for powers of two, you could use a normal mask, but that is only
		445	worth it if, at compile time, you can detect this case. This is the case
		446	when the passed number is a constant and also a power of two (C<n & (n -
		447	1) == 0>):
		448
		449	ecb_inline uint32_t
		450	rndm (uint32_t n)
		451	{
		452	return is_constant (n) && !(n & (n - 1))
		453	? rndm16 () & (num - 1)
		454	: (n * (uint32_t)rndm16 ()) >> 16;
		455	}
		456
23	=item bool ecb_expect(expr,value)	457	=item ecb_expect (expr, value)
24		458
25	=item bool ecb_unlikely(bool)	459	Evaluates C<expr> and returns it. In addition, it tells the compiler that
		460	the C<expr> evaluates to C<value> a lot, which can be used for static
		461	branch optimisations.
26		462
27	=item bool ecb_likely(bool)	463	Usually, you want to use the more intuitive C<ecb_expect_true> and
		464	C<ecb_expect_false> functions instead.
28		465
		466	=item bool ecb_expect_true (cond)
		467
		468	=item bool ecb_expect_false (cond)
		469
		470	These two functions expect a expression that is true or false and return
		471	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
		472	other conditional statement, it will not change the program:
		473
		474	/* these two do the same thing */
		475	if (some_condition) ...;
		476	if (ecb_expect_true (some_condition)) ...;
		477
		478	However, by using C<ecb_expect_true>, you tell the compiler that the
		479	condition is likely to be true (and for C<ecb_expect_false>, that it is
		480	unlikely to be true).
		481
		482	For example, when you check for a null pointer and expect this to be a
		483	rare, exceptional, case, then use C<ecb_expect_false>:
		484
		485	void my_free (void *ptr)
		486	{
		487	if (ecb_expect_false (ptr == 0))
		488	return;
		489	}
		490
		491	Consequent use of these functions to mark away exceptional cases or to
		492	tell the compiler what the hot path through a function is can increase
		493	performance considerably.
		494
		495	You might know these functions under the name C<likely> and C<unlikely>
		496	- while these are common aliases, we find that the expect name is easier
		497	to understand when quickly skimming code. If you wish, you can use
		498	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		499	C<ecb_expect_false> - these are simply aliases.
		500
		501	A very good example is in a function that reserves more space for some
		502	memory block (for example, inside an implementation of a string stream) -
		503	each time something is added, you have to check for a buffer overrun, but
		504	you expect that most checks will turn out to be false:
		505
		506	/* make sure we have "size" extra room in our buffer */
		507	ecb_inline void
		508	reserve (int size)
		509	{
		510	if (ecb_expect_false (current + size > end))
		511	real_reserve_method (size); /* presumably noinline */
		512	}
		513
29	=item bool ecb_assume(cond)	514	=item ecb_assume (cond)
30		515
		516	Tries to tell the compiler that some condition is true, even if it's not
		517	obvious. This is not a function, but a statement: it cannot be used in
		518	another expression.
		519
		520	This can be used to teach the compiler about invariants or other
		521	conditions that might improve code generation, but which are impossible to
		522	deduce form the code itself.
		523
		524	For example, the example reservation function from the C<ecb_expect_false>
		525	description could be written thus (only C<ecb_assume> was added):
		526
		527	ecb_inline void
		528	reserve (int size)
		529	{
		530	if (ecb_expect_false (current + size > end))
		531	real_reserve_method (size); /* presumably noinline */
		532
		533	ecb_assume (current + size <= end);
		534	}
		535
		536	If you then call this function twice, like this:
		537
		538	reserve (10);
		539	reserve (1);
		540
		541	Then the compiler I<might> be able to optimise out the second call
		542	completely, as it knows that C<< current + 1 > end >> is false and the
		543	call will never be executed.
		544
31	=item bool ecb_unreachable()	545	=item ecb_unreachable ()
32		546
		547	This function does nothing itself, except tell the compiler that it will
		548	never be executed. Apart from suppressing a warning in some cases, this
		549	function can be used to implement C<ecb_assume> or similar functionality.
		550
33	=item bool ecb_prefetch(addr,rw,locality)	551	=item ecb_prefetch (addr, rw, locality)
34		552
		553	Tells the compiler to try to prefetch memory at the given C<addr>ess
		554	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
		555	C<0> means that there will only be one access later, C<3> means that
		556	the data will likely be accessed very often, and values in between mean
		557	something... in between. The memory pointed to by the address does not
		558	need to be accessible (it could be a null pointer for example), but C<rw>
		559	and C<locality> must be compile-time constants.
		560
		561	This is a statement, not a function: you cannot use it as part of an
		562	expression.
		563
		564	An obvious way to use this is to prefetch some data far away, in a big
		565	array you loop over. This prefetches memory some 128 array elements later,
		566	in the hope that it will be ready when the CPU arrives at that location.
		567
		568	int sum = 0;
		569
		570	for (i = 0; i < N; ++i)
		571	{
		572	sum += arr [i]
		573	ecb_prefetch (arr + i + 128, 0, 0);
		574	}
		575
		576	It's hard to predict how far to prefetch, and most CPUs that can prefetch
		577	are often good enough to predict this kind of behaviour themselves. It
		578	gets more interesting with linked lists, especially when you do some fair
		579	processing on each list element:
		580
		581	for (node *n = start; n; n = n->next)
		582	{
		583	ecb_prefetch (n->next, 0, 0);
		584	... do medium amount of work with *n
		585	}
		586
		587	After processing the node, (part of) the next node might already be in
		588	cache.
		589
35	=back	590	=back
36		591
37	=head2 BIT FIDDLING / BITSTUFFS	592	=head2 BIT FIDDLING / BIT WIZARDRY
38		593
		594	=over
		595
39	bool ecb_big_endian ();	596	=item bool ecb_big_endian ()
		597
40	bool ecb_little_endian ();	598	=item bool ecb_little_endian ()
		599
		600	These two functions return true if the byte order is big endian
		601	(most-significant byte first) or little endian (least-significant byte
		602	first) respectively.
		603
		604	On systems that are neither, their return values are unspecified.
		605
41	int ecb_ctz32 (uint32_t x);	606	=item int ecb_ctz32 (uint32_t x)
		607
		608	=item int ecb_ctz64 (uint64_t x)
		609
		610	=item int ecb_ctz (T x) [C++]
		611
		612	Returns the index of the least significant bit set in C<x> (or
		613	equivalently the number of bits set to 0 before the least significant bit
		614	set), starting from 0. If C<x> is 0 the result is undefined.
		615
		616	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		617
		618	The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
		619	C<uint32_t> and C<uint64_t> types.
		620
		621	For example:
		622
		623	ecb_ctz32 (3) = 0
		624	ecb_ctz32 (6) = 1
		625
		626	=item bool ecb_is_pot32 (uint32_t x)
		627
		628	=item bool ecb_is_pot64 (uint32_t x)
		629
		630	=item bool ecb_is_pot (T x) [C++]
		631
		632	Returns true iff C<x> is a power of two or C<x == 0>.
		633
		634	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		635
		636	The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
		637	C<uint32_t> and C<uint64_t> types.
		638
		639	=item int ecb_ld32 (uint32_t x)
		640
		641	=item int ecb_ld64 (uint64_t x)
		642
		643	=item int ecb_ld64 (T x) [C++]
		644
		645	Returns the index of the most significant bit set in C<x>, or the number
		646	of digits the number requires in binary (so that C<< 2**ld <= x <
		647	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		648	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		649	example to see how many bits a certain number requires to be encoded.
		650
		651	This function is similar to the "count leading zero bits" function, except
		652	that that one returns how many zero bits are "in front" of the number (in
		653	the given data type), while C<ecb_ld> returns how many bits the number
		654	itself requires.
		655
		656	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		657
		658	The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
		659	C<uint32_t> and C<uint64_t> types.
		660
42	int ecb_popcount32 (uint32_t x);	661	=item int ecb_popcount32 (uint32_t x)
		662
		663	=item int ecb_popcount64 (uint64_t x)
		664
		665	=item int ecb_popcount (T x) [C++]
		666
		667	Returns the number of bits set to 1 in C<x>.
		668
		669	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		670
		671	The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
		672	C<uint32_t> and C<uint64_t> types.
		673
		674	For example:
		675
		676	ecb_popcount32 (7) = 3
		677	ecb_popcount32 (255) = 8
		678
		679	=item uint8_t ecb_bitrev8 (uint8_t x)
		680
		681	=item uint16_t ecb_bitrev16 (uint16_t x)
		682
43	uint32_t ecb_bswap32 (uint32_t x);	683	=item uint32_t ecb_bitrev32 (uint32_t x)
		684
		685	=item T ecb_bitrev (T x) [C++]
		686
		687	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		688	and so on.
		689
		690	The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
		691
		692	Example:
		693
		694	ecb_bitrev8 (0xa7) = 0xea
		695	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		696
		697	=item T ecb_bitrev (T x) [C++]
		698
		699	Overloaded C++ bitrev function.
		700
		701	C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
		702
44	uint32_t ecb_bswap16 (uint32_t x);	703	=item uint32_t ecb_bswap16 (uint32_t x)
		704
		705	=item uint32_t ecb_bswap32 (uint32_t x)
		706
		707	=item uint64_t ecb_bswap64 (uint64_t x)
		708
		709	=item T ecb_bswap (T x)
		710
		711	These functions return the value of the 16-bit (32-bit, 64-bit) value
		712	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		713	C<ecb_bswap32>).
		714
		715	The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
		716	C<uint32_t> and C<uint64_t> types.
		717
45	uint32_t ecb_rotr32 (uint32_t x, unsigned int count);	718	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		719
		720	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		721
46	uint32_t ecb_rotl32 (uint32_t x, unsigned int count);	722	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		723
		724	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		725
		726	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		727
		728	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
		729
		730	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
		731
		732	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
		733
		734	These two families of functions return the value of C<x> after rotating
		735	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		736	(C<ecb_rotl>).
		737
		738	Current GCC/clang versions understand these functions and usually compile
		739	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
		740	on x86).
		741
		742	=item T ecb_rotl (T x, unsigned int count) [C++]
		743
		744	=item T ecb_rotr (T x, unsigned int count) [C++]
		745
		746	Overloaded C++ rotl/rotr functions.
		747
		748	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		749
		750	=back
		751
		752	=head2 HOST ENDIANNESS CONVERSION
		753
		754	=over
		755
		756	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		757
		758	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		759
		760	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		761
		762	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		763
		764	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		765
		766	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		767
		768	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		769
		770	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		771	where C<be> and C<le> stand for big endian and little endian, respectively.
		772
		773	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		774
		775	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		776
		777	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		778
		779	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		780
		781	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		782
		783	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		784
		785	Like above, but converts I<from> host byte order to the specified
		786	endianness.
		787
		788	=back
		789
		790	In C++ the following additional template functions are supported:
		791
		792	=over
		793
		794	=item T ecb_be_to_host (T v)
		795
		796	=item T ecb_le_to_host (T v)
		797
		798	=item T ecb_host_to_be (T v)
		799
		800	=item T ecb_host_to_le (T v)
		801
		802	=back
		803
		804	These functions work like their C counterparts, above, but use templates,
		805	which make them useful in generic code.
		806
		807	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		808	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		809	again can be useful in generic code).
		810
		811	=head2 UNALIGNED LOAD/STORE
		812
		813	These function load or store unaligned multi-byte values.
		814
		815	=over
		816
		817	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		818
		819	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		820
		821	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		822
		823	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		824	memory.
		825
		826	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		827
		828	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		829
		830	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		831
		832	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		833
		834	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		835
		836	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		837
		838	Like above, but additionally convert from big endian (C<be>) or little
		839	endian (C<le>) byte order to host byte order while doing so.
		840
		841	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		842
		843	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		844
		845	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		846
		847	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		848	memory.
		849
		850	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		851
		852	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		853
		854	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		855
		856	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		857
		858	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		859
		860	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		861
		862	Like above, but additionally convert from host byte order to big endian
		863	(C<be>) or little endian (C<le>) byte order while doing so.
		864
		865	=back
		866
		867	In C++ the following additional template functions are supported:
		868
		869	=over
		870
		871	=item T ecb_peek<T> (const void *ptr)
		872
		873	=item T ecb_peek_be<T> (const void *ptr)
		874
		875	=item T ecb_peek_le<T> (const void *ptr)
		876
		877	=item T ecb_peek_u<T> (const void *ptr)
		878
		879	=item T ecb_peek_be_u<T> (const void *ptr)
		880
		881	=item T ecb_peek_le_u<T> (const void *ptr)
		882
		883	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		884	32 or 64 bit value from memory, with optional conversion from big/little
		885	endian.
		886
		887	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		888
		889	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		890
		891	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		892
		893	Unlike their C counterparts, these functions support 8 bit quantities
		894	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		895	all of which hopefully makes them more useful in generic code.
		896
		897	=item ecb_poke (void *ptr, T v)
		898
		899	=item ecb_poke_be (void *ptr, T v)
		900
		901	=item ecb_poke_le (void *ptr, T v)
		902
		903	=item ecb_poke_u (void *ptr, T v)
		904
		905	=item ecb_poke_be_u (void *ptr, T v)
		906
		907	=item ecb_poke_le_u (void *ptr, T v)
		908
		909	Again, similarly to their C counterparts, these functions store an
		910	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		911	big/little endian.
		912
		913	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		914
		915	Unlike their C counterparts, these functions support 8 bit quantities
		916	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		917	all of which hopefully makes them more useful in generic code.
		918
		919	=back
		920
		921	=head2 FLOATING POINT FIDDLING
		922
		923	=over
		924
		925	=item ECB_INFINITY [-UECB_NO_LIBM]
		926
		927	Evaluates to positive infinity if supported by the platform, otherwise to
		928	a truly huge number.
		929
		930	=item ECB_NAN [-UECB_NO_LIBM]
		931
		932	Evaluates to a quiet NAN if supported by the platform, otherwise to
		933	C<ECB_INFINITY>.
		934
		935	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		936
		937	Same as C<ldexpf>, but always available.
		938
		939	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		940
		941	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		942
		943	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		944
		945	These functions each take an argument in the native C<float> or C<double>
		946	type and return the IEEE 754 bit representation of it (binary16/half,
		947	binary32/single or binary64/double precision).
		948
		949	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		950	will be the most significant bit, followed by exponent and mantissa.
		951
		952	This function should work even when the native floating point format isn't
		953	IEEE compliant, of course at a speed and code size penalty, and of course
		954	also within reasonable limits (it tries to convert NaNs, infinities and
		955	denormals, but will likely convert negative zero to positive zero).
		956
		957	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		958	be able to optimise away this function completely.
		959
		960	These functions can be helpful when serialising floats to the network - you
		961	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		962
		963	Another use for these functions is to manipulate floating point values
		964	directly.
		965
		966	Silly example: toggle the sign bit of a float.
		967
		968	/* On gcc-4.7 on amd64, */
		969	/* this results in a single add instruction to toggle the bit, and 4 extra */
		970	/* instructions to move the float value to an integer register and back. */
		971
		972	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		973
		974	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		975
		976	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		977
		978	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		979
		980	The reverse operation of the previous function - takes the bit
		981	representation of an IEEE binary16, binary32 or binary64 number (half,
		982	single or double precision) and converts it to the native C<float> or
		983	C<double> format.
		984
		985	This function should work even when the native floating point format isn't
		986	IEEE compliant, of course at a speed and code size penalty, and of course
		987	also within reasonable limits (it tries to convert normals and denormals,
		988	and might be lucky for infinities, and with extraordinary luck, also for
		989	negative zero).
		990
		991	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		992	be able to optimise away this function completely.
		993
		994	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		995
		996	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		997
		998	Convert a IEEE binary32/single precision to binary16/half format, and vice
		999	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1000	and NaNs) correctly.
		1001
		1002	These are functions are available under C<-DECB_NO_LIBM>, since
		1003	they do not rely on the platform floating point format. The
		1004	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1005	usually what you want.
		1006
		1007	=back
47		1008
48	=head2 ARITHMETIC	1009	=head2 ARITHMETIC
49		1010
		1011	=over
		1012
50	x = ecb_mod (m, n)	1013	=item x = ecb_mod (m, n)
		1014
		1015	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1016	of the division operation between C<m> and C<n>, using floored
		1017	division. Unlike the C remainder operator C<%>, this function ensures that
		1018	the return value is always positive and that the two numbers I<m> and
		1019	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1020	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1021	in the language.
		1022
		1023	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
		1024	negatable, that is, both C<m> and C<-m> must be representable in its
		1025	type (this typically excludes the minimum signed integer value, the same
		1026	limitation as for C</> and C<%> in C).
		1027
		1028	Current GCC/clang versions compile this into an efficient branchless
		1029	sequence on almost all CPUs.
		1030
		1031	For example, when you want to rotate forward through the members of an
		1032	array for increasing C<m> (which might be negative), then you should use
		1033	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1034	change direction for negative values:
		1035
		1036	for (m = -100; m <= 100; ++m)
		1037	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1038
		1039	=item x = ecb_div_rd (val, div)
		1040
		1041	=item x = ecb_div_ru (val, div)
		1042
		1043	Returns C<val> divided by C<div> rounded down or up, respectively.
		1044	C<val> and C<div> must have integer types and C<div> must be strictly
		1045	positive. Note that these functions are implemented with macros in C
		1046	and with function templates in C++.
		1047
		1048	=back
51		1049
52	=head2 UTILITY	1050	=head2 UTILITY
53		1051
54	ecb_array_length (name)	1052	=over
55		1053
		1054	=item element_count = ecb_array_length (name)
56		1055
		1056	Returns the number of elements in the array C<name>. For example:
		1057
		1058	int primes[] = { 2, 3, 5, 7, 11 };
		1059	int sum = 0;
		1060
		1061	for (i = 0; i < ecb_array_length (primes); i++)
		1062	sum += primes [i];
		1063
		1064	=back
		1065
		1066	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
		1067
		1068	These symbols need to be defined before including F<ecb.h> the first time.
		1069
		1070	=over
		1071
		1072	=item ECB_NO_THREADS
		1073
		1074	If F<ecb.h> is never used from multiple threads, then this symbol can
		1075	be defined, in which case memory fences (and similar constructs) are
		1076	completely removed, leading to more efficient code and fewer dependencies.
		1077
		1078	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1079
		1080	=item ECB_NO_SMP
		1081
		1082	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1083	multiple threads, but never concurrently (e.g. if the system the program
		1084	runs on has only a single CPU with a single core, no hyperthreading and so
		1085	on), then this symbol can be defined, leading to more efficient code and
		1086	fewer dependencies.
		1087
		1088	=item ECB_NO_LIBM
		1089
		1090	When defined to C<1>, do not export any functions that might introduce
		1091	dependencies on the math library (usually called F<-lm>) - these are
		1092	marked with [-UECB_NO_LIBM].
		1093
		1094	=back
		1095
		1096	=head1 UNDOCUMENTED FUNCTIONALITY
		1097
		1098	F<ecb.h> is full of undocumented functionality as well, some of which is
		1099	intended to be internal-use only, some of which we forgot to document, and
		1100	some of which we hide because we are not sure we will keep the interface
		1101	stable.
		1102
		1103	While you are welcome to rummage around and use whatever you find useful
		1104	(we can't stop you), keep in mind that we will change undocumented
		1105	functionality in incompatible ways without thinking twice, while we are
		1106	considerably more conservative with documented things.
		1107
		1108	=head1 AUTHORS
		1109
		1110	C<libecb> is designed and maintained by:
		1111
		1112	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1113	Marc Alexander Lehmann <schmorp@schmorp.de>
		1114
		1115

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Comparing libecb/ecb.pod (file contents): Revision 1.1 by root, Thu May 26 19:39:40 2011 UTC vs. Revision 1.88 by root, Mon Jun 21 21:49:51 2021 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.1 by root, Thu May 26 19:39:40 2011 UTC vs.
Revision 1.88 by root, Mon Jun 21 21:49:51 2021 UTC