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		1	=head1 LIBECB - e-C-Builtins
1		2
2	=head2 GCC ATTRIBUTES	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 GCC built-ins, together
		16	with replacement functions for other compilers. In addition to this,
		17	it provides a number of other lowlevel C utilities, such as endianness
		18	detection, byte swapping or bit rotations.
		19
		20	Or in other words, things that should be built into any standard C system,
		21	but aren't, implemented as efficient as possible with GCC, and still
		22	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_t int16_t uint16_t
		64	int32_t uint32_t int64_t uint64_t
		65	intptr_t uintptr_t
		66
		67	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
		68	platform (currently C<4> or C<8>) and can be used in preprocessor
		69	expressions.
		70
		71	For C<ptrdiff_t> and C<size_t> use C<stddef.h>.
		72
		73	=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
		74
		75	All the following symbols expand to an expression that can be tested in
		76	preprocessor instructions as well as treated as a boolean (use C<!!> to
		77	ensure it's either C<0> or C<1> if you need that).
3		78
4	=over 4	79	=over 4
5		80
6	=item ecb_attribute(attrlist)	81	=item ECB_C
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		82
		83	True if the implementation defines the C<__STDC__> macro to a true value,
		84	while not claiming to be C++.
		85
		86	=item ECB_C99
		87
		88	True if the implementation claims to be compliant to C99 (ISO/IEC
		89	9899:1999) or any later version, while not claiming to be C++.
		90
		91	Note that later versions (ECB_C11) remove core features again (for
		92	example, variable length arrays).
		93
		94	=item ECB_C11
		95
		96	True if the implementation claims to be compliant to C11 (ISO/IEC
		97	9899:2011) or any later version, while not claiming to be C++.
		98
		99	=item ECB_CPP
		100
		101	True if the implementation defines the C<__cplusplus__> macro to a true
		102	value, which is typically true for C++ compilers.
		103
		104	=item ECB_CPP11
		105
		106	True if the implementation claims to be compliant to ISO/IEC 14882:2011
		107	(C++11) or any later version.
		108
		109	=item ECB_GCC_VERSION (major, minor)
		110
		111	Expands to a true value (suitable for testing in by the preprocessor)
		112	if the compiler used is GNU C and the version is the given version, or
		113	higher.
		114
		115	This macro tries to return false on compilers that claim to be GCC
		116	compatible but aren't.
		117
		118	=item ECB_EXTERN_C
		119
		120	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		121
		122	This can be used to declare a single external C function:
		123
		124	ECB_EXTERN_C int printf (const char *format, ...);
		125
		126	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		127
		128	These two macros can be used to wrap multiple C<extern "C"> definitions -
		129	they expand to nothing in C.
		130
		131	They are most useful in header files:
		132
		133	ECB_EXTERN_C_BEG
		134
		135	int mycfun1 (int x);
		136	int mycfun2 (int x);
		137
		138	ECB_EXTERN_C_END
		139
		140	=item ECB_STDFP
		141
		142	If this evaluates to a true value (suitable for testing in by the
		143	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		144	and double/binary64 representations internally I<and> the endianness of
		145	both types match the endianness of C<uint32_t> and C<uint64_t>.
		146
		147	This means you can just copy the bits of a C<float> (or C<double>) to an
		148	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		149	without having to think about format or endianness.
		150
		151	This is true for basically all modern platforms, although F<ecb.h> might
		152	not be able to deduce this correctly everywhere and might err on the safe
		153	side.
		154
		155	=item ECB_AMD64, ECB_AMD64_X32
		156
		157	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		158	ABI, respectively, and undefined elsewhere.
		159
		160	The designers of the new X32 ABI for some inexplicable reason decided to
		161	make it look exactly like amd64, even though it's completely incompatible
		162	to that ABI, breaking about every piece of software that assumed that
		163	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		164	necessary.
		165
15	=back	166	=back
		167
		168	=head2 MACRO TRICKERY
		169
		170	=over 4
		171
		172	=item ECB_CONCAT (a, b)
		173
		174	Expands any macros in C<a> and C<b>, then concatenates the result to form
		175	a single token. This is mainly useful to form identifiers from components,
		176	e.g.:
		177
		178	#define S1 str
		179	#define S2 cpy
		180
		181	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		182
		183	=item ECB_STRINGIFY (arg)
		184
		185	Expands any macros in C<arg> and returns the stringified version of
		186	it. This is mainly useful to get the contents of a macro in string form,
		187	e.g.:
		188
		189	#define SQL_LIMIT 100
		190	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		191
		192	=item ECB_STRINGIFY_EXPR (expr)
		193
		194	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		195	is a valid expression. This is useful to catch typos or cases where the
		196	macro isn't available:
		197
		198	#include <errno.h>
		199
		200	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		201	ECB_STRINGIFY_EXPR (EDOM); // "33"
		202
		203	// now imagine we had a typo:
		204
		205	ECB_STRINGIFY (EDAM); // "EDAM"
		206	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		207
		208	=back
		209
		210	=head2 ATTRIBUTES
		211
		212	A major part of libecb deals with additional attributes that can be
		213	assigned to functions, variables and sometimes even types - much like
		214	C<const> or C<volatile> in C. They are implemented using either GCC
		215	attributes or other compiler/language specific features. Attributes
		216	declarations must be put before the whole declaration:
		217
		218	ecb_const int mysqrt (int a);
		219	ecb_unused int i;
		220
		221	=over 4
		222
		223	=item ecb_unused
		224
		225	Marks a function or a variable as "unused", which simply suppresses a
		226	warning by GCC when it detects it as unused. This is useful when you e.g.
		227	declare a variable but do not always use it:
		228
		229	{
		230	ecb_unused int var;
		231
		232	#ifdef SOMECONDITION
		233	var = ...;
		234	return var;
		235	#else
		236	return 0;
		237	#endif
		238	}
		239
		240	=item ecb_deprecated
		241
		242	Similar to C<ecb_unused>, but marks a function, variable or type as
		243	deprecated. This makes some compilers warn when the type is used.
		244
		245	=item ecb_deprecated_message (message)
		246
		247	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		248	used instead of a generic depreciation message when the object is being
		249	used.
		250
		251	=item ecb_inline
		252
		253	Expands either to C<static inline> or to just C<static>, if inline
		254	isn't supported. It should be used to declare functions that should be
		255	inlined, for code size or speed reasons.
		256
		257	Example: inline this function, it surely will reduce codesize.
		258
		259	ecb_inline int
		260	negmul (int a, int b)
		261	{
		262	return - (a * b);
		263	}
		264
		265	=item ecb_noinline
		266
		267	Prevents a function from being inlined - it might be optimised away, but
		268	not inlined into other functions. This is useful if you know your function
		269	is rarely called and large enough for inlining not to be helpful.
		270
		271	=item ecb_noreturn
		272
		273	Marks a function as "not returning, ever". Some typical functions that
		274	don't return are C<exit> or C<abort> (which really works hard to not
		275	return), and now you can make your own:
		276
		277	ecb_noreturn void
		278	my_abort (const char *errline)
		279	{
		280	puts (errline);
		281	abort ();
		282	}
		283
		284	In this case, the compiler would probably be smart enough to deduce it on
		285	its own, so this is mainly useful for declarations.
		286
		287	=item ecb_restrict
		288
		289	Expands to the C<restrict> keyword or equivalent on compilers that support
		290	them, and to nothing on others. Must be specified on a pointer type or
		291	an array index to indicate that the memory doesn't alias with any other
		292	restricted pointer in the same scope.
		293
		294	Example: multiply a vector, and allow the compiler to parallelise the
		295	loop, because it knows it doesn't overwrite input values.
		296
		297	void
		298	multiply (ecb_restrict float *src,
		299	ecb_restrict float *dst,
		300	int len, float factor)
		301	{
		302	int i;
		303
		304	for (i = 0; i < len; ++i)
		305	dst [i] = src [i] * factor;
		306	}
		307
		308	=item ecb_const
		309
		310	Declares that the function only depends on the values of its arguments,
		311	much like a mathematical function. It specifically does not read or write
		312	any memory any arguments might point to, global variables, or call any
		313	non-const functions. It also must not have any side effects.
		314
		315	Such a function can be optimised much more aggressively by the compiler -
		316	for example, multiple calls with the same arguments can be optimised into
		317	a single call, which wouldn't be possible if the compiler would have to
		318	expect any side effects.
		319
		320	It is best suited for functions in the sense of mathematical functions,
		321	such as a function returning the square root of its input argument.
		322
		323	Not suited would be a function that calculates the hash of some memory
		324	area you pass in, prints some messages or looks at a global variable to
		325	decide on rounding.
		326
		327	See C<ecb_pure> for a slightly less restrictive class of functions.
		328
		329	=item ecb_pure
		330
		331	Similar to C<ecb_const>, declares a function that has no side
		332	effects. Unlike C<ecb_const>, the function is allowed to examine global
		333	variables and any other memory areas (such as the ones passed to it via
		334	pointers).
		335
		336	While these functions cannot be optimised as aggressively as C<ecb_const>
		337	functions, they can still be optimised away in many occasions, and the
		338	compiler has more freedom in moving calls to them around.
		339
		340	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		341	function that calculates the MD5 sum of some input and updates some MD5
		342	state passed as argument would I<NOT> be pure, however, as it would modify
		343	some memory area that is not the return value.
		344
		345	=item ecb_hot
		346
		347	This declares a function as "hot" with regards to the cache - the function
		348	is used so often, that it is very beneficial to keep it in the cache if
		349	possible.
		350
		351	The compiler reacts by trying to place hot functions near to each other in
		352	memory.
		353
		354	Whether a function is hot or not often depends on the whole program,
		355	and less on the function itself. C<ecb_cold> is likely more useful in
		356	practise.
		357
		358	=item ecb_cold
		359
		360	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		361	the cache, or in other words, this function is not called often, or not at
		362	speed-critical times, and keeping it in the cache might be a waste of said
		363	cache.
		364
		365	In addition to placing cold functions together (or at least away from hot
		366	functions), this knowledge can be used in other ways, for example, the
		367	function will be optimised for size, as opposed to speed, and codepaths
		368	leading to calls to those functions can automatically be marked as if
		369	C<ecb_expect_false> had been used to reach them.
		370
		371	Good examples for such functions would be error reporting functions, or
		372	functions only called in exceptional or rare cases.
		373
		374	=item ecb_artificial
		375
		376	Declares the function as "artificial", in this case meaning that this
		377	function is not really meant to be a function, but more like an accessor
		378	- many methods in C++ classes are mere accessor functions, and having a
		379	crash reported in such a method, or single-stepping through them, is not
		380	usually so helpful, especially when it's inlined to just a few instructions.
		381
		382	Marking them as artificial will instruct the debugger about just this,
		383	leading to happier debugging and thus happier lives.
		384
		385	Example: in some kind of smart-pointer class, mark the pointer accessor as
		386	artificial, so that the whole class acts more like a pointer and less like
		387	some C++ abstraction monster.
		388
		389	template<typename T>
		390	struct my_smart_ptr
		391	{
		392	T *value;
		393
		394	ecb_artificial
		395	operator T *()
		396	{
		397	return value;
		398	}
		399	};
		400
		401	=back
16		402
17	=head2 OPTIMISATION HINTS	403	=head2 OPTIMISATION HINTS
18		404
19	=over 4	405	=over 4
20		406
21	=item bool ecb_is_constant(expr)	407	=item bool ecb_is_constant (expr)
22		408
		409	Returns true iff the expression can be deduced to be a compile-time
		410	constant, and false otherwise.
		411
		412	For example, when you have a C<rndm16> function that returns a 16 bit
		413	random number, and you have a function that maps this to a range from
		414	0..n-1, then you could use this inline function in a header file:
		415
		416	ecb_inline uint32_t
		417	rndm (uint32_t n)
		418	{
		419	return (n * (uint32_t)rndm16 ()) >> 16;
		420	}
		421
		422	However, for powers of two, you could use a normal mask, but that is only
		423	worth it if, at compile time, you can detect this case. This is the case
		424	when the passed number is a constant and also a power of two (C<n & (n -
		425	1) == 0>):
		426
		427	ecb_inline uint32_t
		428	rndm (uint32_t n)
		429	{
		430	return is_constant (n) && !(n & (n - 1))
		431	? rndm16 () & (num - 1)
		432	: (n * (uint32_t)rndm16 ()) >> 16;
		433	}
		434
23	=item bool ecb_expect(expr,value)	435	=item ecb_expect (expr, value)
24		436
25	=item bool ecb_unlikely(bool)	437	Evaluates C<expr> and returns it. In addition, it tells the compiler that
		438	the C<expr> evaluates to C<value> a lot, which can be used for static
		439	branch optimisations.
26		440
27	=item bool ecb_likely(bool)	441	Usually, you want to use the more intuitive C<ecb_expect_true> and
		442	C<ecb_expect_false> functions instead.
28		443
		444	=item bool ecb_expect_true (cond)
		445
		446	=item bool ecb_expect_false (cond)
		447
		448	These two functions expect a expression that is true or false and return
		449	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
		450	other conditional statement, it will not change the program:
		451
		452	/* these two do the same thing */
		453	if (some_condition) ...;
		454	if (ecb_expect_true (some_condition)) ...;
		455
		456	However, by using C<ecb_expect_true>, you tell the compiler that the
		457	condition is likely to be true (and for C<ecb_expect_false>, that it is
		458	unlikely to be true).
		459
		460	For example, when you check for a null pointer and expect this to be a
		461	rare, exceptional, case, then use C<ecb_expect_false>:
		462
		463	void my_free (void *ptr)
		464	{
		465	if (ecb_expect_false (ptr == 0))
		466	return;
		467	}
		468
		469	Consequent use of these functions to mark away exceptional cases or to
		470	tell the compiler what the hot path through a function is can increase
		471	performance considerably.
		472
		473	You might know these functions under the name C<likely> and C<unlikely>
		474	- while these are common aliases, we find that the expect name is easier
		475	to understand when quickly skimming code. If you wish, you can use
		476	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		477	C<ecb_expect_false> - these are simply aliases.
		478
		479	A very good example is in a function that reserves more space for some
		480	memory block (for example, inside an implementation of a string stream) -
		481	each time something is added, you have to check for a buffer overrun, but
		482	you expect that most checks will turn out to be false:
		483
		484	/* make sure we have "size" extra room in our buffer */
		485	ecb_inline void
		486	reserve (int size)
		487	{
		488	if (ecb_expect_false (current + size > end))
		489	real_reserve_method (size); /* presumably noinline */
		490	}
		491
29	=item bool ecb_assume(cond)	492	=item ecb_assume (cond)
30		493
		494	Tries to tell the compiler that some condition is true, even if it's not
		495	obvious. This is not a function, but a statement: it cannot be used in
		496	another expression.
		497
		498	This can be used to teach the compiler about invariants or other
		499	conditions that might improve code generation, but which are impossible to
		500	deduce form the code itself.
		501
		502	For example, the example reservation function from the C<ecb_expect_false>
		503	description could be written thus (only C<ecb_assume> was added):
		504
		505	ecb_inline void
		506	reserve (int size)
		507	{
		508	if (ecb_expect_false (current + size > end))
		509	real_reserve_method (size); /* presumably noinline */
		510
		511	ecb_assume (current + size <= end);
		512	}
		513
		514	If you then call this function twice, like this:
		515
		516	reserve (10);
		517	reserve (1);
		518
		519	Then the compiler I<might> be able to optimise out the second call
		520	completely, as it knows that C<< current + 1 > end >> is false and the
		521	call will never be executed.
		522
31	=item bool ecb_unreachable()	523	=item ecb_unreachable ()
32		524
		525	This function does nothing itself, except tell the compiler that it will
		526	never be executed. Apart from suppressing a warning in some cases, this
		527	function can be used to implement C<ecb_assume> or similar functionality.
		528
33	=item bool ecb_prefetch(addr,rw,locality)	529	=item ecb_prefetch (addr, rw, locality)
34		530
		531	Tells the compiler to try to prefetch memory at the given C<addr>ess
		532	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
		533	C<0> means that there will only be one access later, C<3> means that
		534	the data will likely be accessed very often, and values in between mean
		535	something... in between. The memory pointed to by the address does not
		536	need to be accessible (it could be a null pointer for example), but C<rw>
		537	and C<locality> must be compile-time constants.
		538
		539	This is a statement, not a function: you cannot use it as part of an
		540	expression.
		541
		542	An obvious way to use this is to prefetch some data far away, in a big
		543	array you loop over. This prefetches memory some 128 array elements later,
		544	in the hope that it will be ready when the CPU arrives at that location.
		545
		546	int sum = 0;
		547
		548	for (i = 0; i < N; ++i)
		549	{
		550	sum += arr [i]
		551	ecb_prefetch (arr + i + 128, 0, 0);
		552	}
		553
		554	It's hard to predict how far to prefetch, and most CPUs that can prefetch
		555	are often good enough to predict this kind of behaviour themselves. It
		556	gets more interesting with linked lists, especially when you do some fair
		557	processing on each list element:
		558
		559	for (node *n = start; n; n = n->next)
		560	{
		561	ecb_prefetch (n->next, 0, 0);
		562	... do medium amount of work with *n
		563	}
		564
		565	After processing the node, (part of) the next node might already be in
		566	cache.
		567
35	=back	568	=back
36		569
37	=head2 BIT FIDDLING / BITSTUFFS	570	=head2 BIT FIDDLING / BIT WIZARDRY
38		571
		572	=over 4
		573
39	bool ecb_big_endian ();	574	=item bool ecb_big_endian ()
		575
40	bool ecb_little_endian ();	576	=item bool ecb_little_endian ()
		577
		578	These two functions return true if the byte order is big endian
		579	(most-significant byte first) or little endian (least-significant byte
		580	first) respectively.
		581
		582	On systems that are neither, their return values are unspecified.
		583
41	int ecb_ctz32 (uint32_t x);	584	=item int ecb_ctz32 (uint32_t x)
		585
		586	=item int ecb_ctz64 (uint64_t x)
		587
		588	Returns the index of the least significant bit set in C<x> (or
		589	equivalently the number of bits set to 0 before the least significant bit
		590	set), starting from 0. If C<x> is 0 the result is undefined.
		591
		592	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		593
		594	For example:
		595
		596	ecb_ctz32 (3) = 0
		597	ecb_ctz32 (6) = 1
		598
		599	=item bool ecb_is_pot32 (uint32_t x)
		600
		601	=item bool ecb_is_pot64 (uint32_t x)
		602
		603	Returns true iff C<x> is a power of two or C<x == 0>.
		604
		605	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		606
		607	=item int ecb_ld32 (uint32_t x)
		608
		609	=item int ecb_ld64 (uint64_t x)
		610
		611	Returns the index of the most significant bit set in C<x>, or the number
		612	of digits the number requires in binary (so that C<< 2**ld <= x <
		613	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		614	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		615	example to see how many bits a certain number requires to be encoded.
		616
		617	This function is similar to the "count leading zero bits" function, except
		618	that that one returns how many zero bits are "in front" of the number (in
		619	the given data type), while C<ecb_ld> returns how many bits the number
		620	itself requires.
		621
		622	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		623
42	int ecb_popcount32 (uint32_t x);	624	=item int ecb_popcount32 (uint32_t x)
		625
		626	=item int ecb_popcount64 (uint64_t x)
		627
		628	Returns the number of bits set to 1 in C<x>.
		629
		630	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		631
		632	For example:
		633
		634	ecb_popcount32 (7) = 3
		635	ecb_popcount32 (255) = 8
		636
		637	=item uint8_t ecb_bitrev8 (uint8_t x)
		638
		639	=item uint16_t ecb_bitrev16 (uint16_t x)
		640
43	uint32_t ecb_bswap32 (uint32_t x);	641	=item uint32_t ecb_bitrev32 (uint32_t x)
		642
		643	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		644	and so on.
		645
		646	Example:
		647
		648	ecb_bitrev8 (0xa7) = 0xea
		649	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		650
44	uint32_t ecb_bswap16 (uint32_t x);	651	=item uint32_t ecb_bswap16 (uint32_t x)
		652
		653	=item uint32_t ecb_bswap32 (uint32_t x)
		654
		655	=item uint64_t ecb_bswap64 (uint64_t x)
		656
		657	These functions return the value of the 16-bit (32-bit, 64-bit) value
		658	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		659	C<ecb_bswap32>).
		660
45	uint32_t ecb_rotr32 (uint32_t x, unsigned int count);	661	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		662
		663	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		664
46	uint32_t ecb_rotl32 (uint32_t x, unsigned int count);	665	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		666
		667	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		668
		669	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		670
		671	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
		672
		673	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
		674
		675	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
		676
		677	These two families of functions return the value of C<x> after rotating
		678	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		679	(C<ecb_rotl>).
		680
		681	Current GCC versions understand these functions and usually compile them
		682	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		683	x86).
		684
		685	=back
		686
		687	=head2 FLOATING POINT FIDDLING
		688
		689	=over 4
		690
		691	=item ECB_INFINITY
		692
		693	Evaluates to positive infinity if supported by the platform, otherwise to
		694	a truly huge number.
		695
		696	=item ECB_NAN
		697
		698	Evaluates to a quiet NAN if supported by the platform, otherwise to
		699	C<ECB_INFINITY>.
		700
		701	=item float ecb_ldexpf (float x, int exp)
		702
		703	Same as C<ldexpf>, but always available.
		704
		705	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		706
		707	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		708
		709	These functions each take an argument in the native C<float> or C<double>
		710	type and return the IEEE 754 bit representation of it.
		711
		712	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		713	will be the most significant bit, followed by exponent and mantissa.
		714
		715	This function should work even when the native floating point format isn't
		716	IEEE compliant, of course at a speed and code size penalty, and of course
		717	also within reasonable limits (it tries to convert NaNs, infinities and
		718	denormals, but will likely convert negative zero to positive zero).
		719
		720	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		721	be able to optimise away this function completely.
		722
		723	These functions can be helpful when serialising floats to the network - you
		724	can serialise the return value like a normal uint32_t/uint64_t.
		725
		726	Another use for these functions is to manipulate floating point values
		727	directly.
		728
		729	Silly example: toggle the sign bit of a float.
		730
		731	/* On gcc-4.7 on amd64, */
		732	/* this results in a single add instruction to toggle the bit, and 4 extra */
		733	/* instructions to move the float value to an integer register and back. */
		734
		735	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		736
		737	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		738
		739	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		740
		741	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		742
		743	The reverse operation of the previous function - takes the bit
		744	representation of an IEEE binary16, binary32 or binary64 number and
		745	converts it to the native C<float> or C<double> format.
		746
		747	This function should work even when the native floating point format isn't
		748	IEEE compliant, of course at a speed and code size penalty, and of course
		749	also within reasonable limits (it tries to convert normals and denormals,
		750	and might be lucky for infinities, and with extraordinary luck, also for
		751	negative zero).
		752
		753	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		754	be able to optimise away this function completely.
		755
		756	=back
47		757
48	=head2 ARITHMETIC	758	=head2 ARITHMETIC
49		759
		760	=over 4
		761
50	x = ecb_mod (m, n)	762	=item x = ecb_mod (m, n)
		763
		764	Returns C<m> modulo C<n>, which is the same as the positive remainder
		765	of the division operation between C<m> and C<n>, using floored
		766	division. Unlike the C remainder operator C<%>, this function ensures that
		767	the return value is always positive and that the two numbers I<m> and
		768	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		769	C<ecb_mod> implements the mathematical modulo operation, which is missing
		770	in the language.
		771
		772	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
		773	negatable, that is, both C<m> and C<-m> must be representable in its
		774	type (this typically excludes the minimum signed integer value, the same
		775	limitation as for C</> and C<%> in C).
		776
		777	Current GCC versions compile this into an efficient branchless sequence on
		778	almost all CPUs.
		779
		780	For example, when you want to rotate forward through the members of an
		781	array for increasing C<m> (which might be negative), then you should use
		782	C<ecb_mod>, as the C<%> operator might give either negative results, or
		783	change direction for negative values:
		784
		785	for (m = -100; m <= 100; ++m)
		786	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		787
		788	=item x = ecb_div_rd (val, div)
		789
		790	=item x = ecb_div_ru (val, div)
		791
		792	Returns C<val> divided by C<div> rounded down or up, respectively.
		793	C<val> and C<div> must have integer types and C<div> must be strictly
		794	positive. Note that these functions are implemented with macros in C
		795	and with function templates in C++.
		796
		797	=back
51		798
52	=head2 UTILITY	799	=head2 UTILITY
53		800
54	ecb_array_length (name)	801	=over 4
55		802
		803	=item element_count = ecb_array_length (name)
56		804
		805	Returns the number of elements in the array C<name>. For example:
		806
		807	int primes[] = { 2, 3, 5, 7, 11 };
		808	int sum = 0;
		809
		810	for (i = 0; i < ecb_array_length (primes); i++)
		811	sum += primes [i];
		812
		813	=back
		814
		815	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
		816
		817	These symbols need to be defined before including F<ecb.h> the first time.
		818
		819	=over 4
		820
		821	=item ECB_NO_THREADS
		822
		823	If F<ecb.h> is never used from multiple threads, then this symbol can
		824	be defined, in which case memory fences (and similar constructs) are
		825	completely removed, leading to more efficient code and fewer dependencies.
		826
		827	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		828
		829	=item ECB_NO_SMP
		830
		831	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		832	multiple threads, but never concurrently (e.g. if the system the program
		833	runs on has only a single CPU with a single core, no hyperthreading and so
		834	on), then this symbol can be defined, leading to more efficient code and
		835	fewer dependencies.
		836
		837	=item ECB_NO_LIBM
		838
		839	When defined to C<1>, do not export any functions that might introduce
		840	dependencies on the math library (usually called F<-lm>) - these are
		841	marked with [-UECB_NO_LIBM].
		842
		843	=back
		844
		845

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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 1.67 by root, Fri Feb 20 15:53:36 2015 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 1.67 by root, Fri Feb 20 15:53:36 2015 UTC