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		1	=head1 LIBECB - e-C-Builtins
		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 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/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).
		78
		79	=over 4
		80
		81	=item ECB_C
		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
		166	=back
1		167
2	=head2 GCC ATTRIBUTES	168	=head2 GCC ATTRIBUTES
3		169
		170	A major part of libecb deals with GCC attributes. These are additional
		171	attributes that you can assign to functions, variables and sometimes even
		172	types - much like C<const> or C<volatile> in C.
		173
		174	While GCC allows declarations to show up in many surprising places,
		175	but not in many expected places, the safest way is to put attribute
		176	declarations before the whole declaration:
		177
		178	ecb_const int mysqrt (int a);
		179	ecb_unused int i;
		180
		181	For variables, it is often nicer to put the attribute after the name, and
		182	avoid multiple declarations using commas:
		183
		184	int i ecb_unused;
		185
4	=over 4	186	=over 4
5		187
6	=item ecb_attribute(attrlist)	188	=item ecb_attribute ((attrs...))
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		189
		190	A simple wrapper that expands to C<__attribute__((attrs))> on GCC 3.1+ and
		191	Clang 2.8+, and to nothing on other compilers, so the effect is that only
		192	GCC and Clang see these.
		193
		194	Example: use the C<deprecated> attribute on a function.
		195
		196	ecb_attribute((__deprecated__)) void
		197	do_not_use_me_anymore (void);
		198
		199	=item ecb_unused
		200
		201	Marks a function or a variable as "unused", which simply suppresses a
		202	warning by GCC when it detects it as unused. This is useful when you e.g.
		203	declare a variable but do not always use it:
		204
		205	{
		206	int var ecb_unused;
		207
		208	#ifdef SOMECONDITION
		209	var = ...;
		210	return var;
		211	#else
		212	return 0;
		213	#endif
		214	}
		215
		216	=item ecb_deprecated
		217
		218	Similar to C<ecb_unused>, but marks a function, variable or type as
		219	deprecated. This makes some compilers warn when the type is used.
		220
		221	=item ecb_inline
		222
		223	This is not actually an attribute, but you use it like one. It expands
		224	either to C<static inline> or to just C<static>, if inline isn't
		225	supported. It should be used to declare functions that should be inlined,
		226	for code size or speed reasons.
		227
		228	Example: inline this function, it surely will reduce codesize.
		229
		230	ecb_inline int
		231	negmul (int a, int b)
		232	{
		233	return - (a * b);
		234	}
		235
		236	=item ecb_noinline
		237
		238	Prevent a function from being inlined - it might be optimised away, but
		239	not inlined into other functions. This is useful if you know your function
		240	is rarely called and large enough for inlining not to be helpful.
		241
		242	=item ecb_noreturn
		243
		244	Marks a function as "not returning, ever". Some typical functions that
		245	don't return are C<exit> or C<abort> (which really works hard to not
		246	return), and now you can make your own:
		247
		248	ecb_noreturn void
		249	my_abort (const char *errline)
		250	{
		251	puts (errline);
		252	abort ();
		253	}
		254
		255	In this case, the compiler would probably be smart enough to deduce it on
		256	its own, so this is mainly useful for declarations.
		257
		258	=item ecb_restrict
		259
		260	Expands to the C<restrict> keyword or equivalent on compilers that support
		261	them, and to nothing on others. Must be specified on a pointer type or
		262	an array index to indicate that the memory doesn't alias with any other
		263	restricted pointer in the same scope.
		264
		265	Example: multiply a vector, and allow the compiler to parallelise the
		266	loop, because it knows it doesn't overwrite input values.
		267
		268	void
		269	multiply (float *ecb_restrict src,
		270	float *ecb_restrict dst,
		271	int len, float factor)
		272	{
		273	int i;
		274
		275	for (i = 0; i < len; ++i)
		276	dst [i] = src [i] * factor;
		277	}
		278
		279	=item ecb_const
		280
		281	Declares that the function only depends on the values of its arguments,
		282	much like a mathematical function. It specifically does not read or write
		283	any memory any arguments might point to, global variables, or call any
		284	non-const functions. It also must not have any side effects.
		285
		286	Such a function can be optimised much more aggressively by the compiler -
		287	for example, multiple calls with the same arguments can be optimised into
		288	a single call, which wouldn't be possible if the compiler would have to
		289	expect any side effects.
		290
		291	It is best suited for functions in the sense of mathematical functions,
		292	such as a function returning the square root of its input argument.
		293
		294	Not suited would be a function that calculates the hash of some memory
		295	area you pass in, prints some messages or looks at a global variable to
		296	decide on rounding.
		297
		298	See C<ecb_pure> for a slightly less restrictive class of functions.
		299
		300	=item ecb_pure
		301
		302	Similar to C<ecb_const>, declares a function that has no side
		303	effects. Unlike C<ecb_const>, the function is allowed to examine global
		304	variables and any other memory areas (such as the ones passed to it via
		305	pointers).
		306
		307	While these functions cannot be optimised as aggressively as C<ecb_const>
		308	functions, they can still be optimised away in many occasions, and the
		309	compiler has more freedom in moving calls to them around.
		310
		311	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		312	function that calculates the MD5 sum of some input and updates some MD5
		313	state passed as argument would I<NOT> be pure, however, as it would modify
		314	some memory area that is not the return value.
		315
		316	=item ecb_hot
		317
		318	This declares a function as "hot" with regards to the cache - the function
		319	is used so often, that it is very beneficial to keep it in the cache if
		320	possible.
		321
		322	The compiler reacts by trying to place hot functions near to each other in
		323	memory.
		324
		325	Whether a function is hot or not often depends on the whole program,
		326	and less on the function itself. C<ecb_cold> is likely more useful in
		327	practise.
		328
		329	=item ecb_cold
		330
		331	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		332	the cache, or in other words, this function is not called often, or not at
		333	speed-critical times, and keeping it in the cache might be a waste of said
		334	cache.
		335
		336	In addition to placing cold functions together (or at least away from hot
		337	functions), this knowledge can be used in other ways, for example, the
		338	function will be optimised for size, as opposed to speed, and codepaths
		339	leading to calls to those functions can automatically be marked as if
		340	C<ecb_expect_false> had been used to reach them.
		341
		342	Good examples for such functions would be error reporting functions, or
		343	functions only called in exceptional or rare cases.
		344
		345	=item ecb_artificial
		346
		347	Declares the function as "artificial", in this case meaning that this
		348	function is not really meant to be a function, but more like an accessor
		349	- many methods in C++ classes are mere accessor functions, and having a
		350	crash reported in such a method, or single-stepping through them, is not
		351	usually so helpful, especially when it's inlined to just a few instructions.
		352
		353	Marking them as artificial will instruct the debugger about just this,
		354	leading to happier debugging and thus happier lives.
		355
		356	Example: in some kind of smart-pointer class, mark the pointer accessor as
		357	artificial, so that the whole class acts more like a pointer and less like
		358	some C++ abstraction monster.
		359
		360	template<typename T>
		361	struct my_smart_ptr
		362	{
		363	T *value;
		364
		365	ecb_artificial
		366	operator T *()
		367	{
		368	return value;
		369	}
		370	};
		371
15	=back	372	=back
16		373
17	=head2 OPTIMISATION HINTS	374	=head2 OPTIMISATION HINTS
18		375
19	=over 4	376	=over 4
20		377
21	=item bool ecb_is_constant(expr)	378	=item bool ecb_is_constant(expr)
22		379
		380	Returns true iff the expression can be deduced to be a compile-time
		381	constant, and false otherwise.
		382
		383	For example, when you have a C<rndm16> function that returns a 16 bit
		384	random number, and you have a function that maps this to a range from
		385	0..n-1, then you could use this inline function in a header file:
		386
		387	ecb_inline uint32_t
		388	rndm (uint32_t n)
		389	{
		390	return (n * (uint32_t)rndm16 ()) >> 16;
		391	}
		392
		393	However, for powers of two, you could use a normal mask, but that is only
		394	worth it if, at compile time, you can detect this case. This is the case
		395	when the passed number is a constant and also a power of two (C<n & (n -
		396	1) == 0>):
		397
		398	ecb_inline uint32_t
		399	rndm (uint32_t n)
		400	{
		401	return is_constant (n) && !(n & (n - 1))
		402	? rndm16 () & (num - 1)
		403	: (n * (uint32_t)rndm16 ()) >> 16;
		404	}
		405
23	=item bool ecb_expect(expr,value)	406	=item bool ecb_expect (expr, value)
24		407
25	=item bool ecb_unlikely(bool)	408	Evaluates C<expr> and returns it. In addition, it tells the compiler that
		409	the C<expr> evaluates to C<value> a lot, which can be used for static
		410	branch optimisations.
26		411
27	=item bool ecb_likely(bool)	412	Usually, you want to use the more intuitive C<ecb_expect_true> and
		413	C<ecb_expect_false> functions instead.
28		414
		415	=item bool ecb_expect_true (cond)
		416
		417	=item bool ecb_expect_false (cond)
		418
		419	These two functions expect a expression that is true or false and return
		420	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
		421	other conditional statement, it will not change the program:
		422
		423	/* these two do the same thing */
		424	if (some_condition) ...;
		425	if (ecb_expect_true (some_condition)) ...;
		426
		427	However, by using C<ecb_expect_true>, you tell the compiler that the
		428	condition is likely to be true (and for C<ecb_expect_false>, that it is
		429	unlikely to be true).
		430
		431	For example, when you check for a null pointer and expect this to be a
		432	rare, exceptional, case, then use C<ecb_expect_false>:
		433
		434	void my_free (void *ptr)
		435	{
		436	if (ecb_expect_false (ptr == 0))
		437	return;
		438	}
		439
		440	Consequent use of these functions to mark away exceptional cases or to
		441	tell the compiler what the hot path through a function is can increase
		442	performance considerably.
		443
		444	You might know these functions under the name C<likely> and C<unlikely>
		445	- while these are common aliases, we find that the expect name is easier
		446	to understand when quickly skimming code. If you wish, you can use
		447	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		448	C<ecb_expect_false> - these are simply aliases.
		449
		450	A very good example is in a function that reserves more space for some
		451	memory block (for example, inside an implementation of a string stream) -
		452	each time something is added, you have to check for a buffer overrun, but
		453	you expect that most checks will turn out to be false:
		454
		455	/* make sure we have "size" extra room in our buffer */
		456	ecb_inline void
		457	reserve (int size)
		458	{
		459	if (ecb_expect_false (current + size > end))
		460	real_reserve_method (size); /* presumably noinline */
		461	}
		462
29	=item bool ecb_assume(cond)	463	=item bool ecb_assume (cond)
30		464
		465	Try to tell the compiler that some condition is true, even if it's not
		466	obvious.
		467
		468	This can be used to teach the compiler about invariants or other
		469	conditions that might improve code generation, but which are impossible to
		470	deduce form the code itself.
		471
		472	For example, the example reservation function from the C<ecb_expect_false>
		473	description could be written thus (only C<ecb_assume> was added):
		474
		475	ecb_inline void
		476	reserve (int size)
		477	{
		478	if (ecb_expect_false (current + size > end))
		479	real_reserve_method (size); /* presumably noinline */
		480
		481	ecb_assume (current + size <= end);
		482	}
		483
		484	If you then call this function twice, like this:
		485
		486	reserve (10);
		487	reserve (1);
		488
		489	Then the compiler I<might> be able to optimise out the second call
		490	completely, as it knows that C<< current + 1 > end >> is false and the
		491	call will never be executed.
		492
31	=item bool ecb_unreachable()	493	=item bool ecb_unreachable ()
32		494
		495	This function does nothing itself, except tell the compiler that it will
		496	never be executed. Apart from suppressing a warning in some cases, this
		497	function can be used to implement C<ecb_assume> or similar functions.
		498
33	=item bool ecb_prefetch(addr,rw,locality)	499	=item bool ecb_prefetch (addr, rw, locality)
34		500
		501	Tells the compiler to try to prefetch memory at the given C<addr>ess
		502	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
		503	C<0> means that there will only be one access later, C<3> means that
		504	the data will likely be accessed very often, and values in between mean
		505	something... in between. The memory pointed to by the address does not
		506	need to be accessible (it could be a null pointer for example), but C<rw>
		507	and C<locality> must be compile-time constants.
		508
		509	An obvious way to use this is to prefetch some data far away, in a big
		510	array you loop over. This prefetches memory some 128 array elements later,
		511	in the hope that it will be ready when the CPU arrives at that location.
		512
		513	int sum = 0;
		514
		515	for (i = 0; i < N; ++i)
		516	{
		517	sum += arr [i]
		518	ecb_prefetch (arr + i + 128, 0, 0);
		519	}
		520
		521	It's hard to predict how far to prefetch, and most CPUs that can prefetch
		522	are often good enough to predict this kind of behaviour themselves. It
		523	gets more interesting with linked lists, especially when you do some fair
		524	processing on each list element:
		525
		526	for (node *n = start; n; n = n->next)
		527	{
		528	ecb_prefetch (n->next, 0, 0);
		529	... do medium amount of work with *n
		530	}
		531
		532	After processing the node, (part of) the next node might already be in
		533	cache.
		534
35	=back	535	=back
36		536
37	=head2 BIT FIDDLING / BITSTUFFS	537	=head2 BIT FIDDLING / BIT WIZARDRY
38		538
		539	=over 4
		540
39	bool ecb_big_endian ();	541	=item bool ecb_big_endian ()
		542
40	bool ecb_little_endian ();	543	=item bool ecb_little_endian ()
		544
		545	These two functions return true if the byte order is big endian
		546	(most-significant byte first) or little endian (least-significant byte
		547	first) respectively.
		548
		549	On systems that are neither, their return values are unspecified.
		550
41	int ecb_ctz32 (uint32_t x);	551	=item int ecb_ctz32 (uint32_t x)
		552
		553	=item int ecb_ctz64 (uint64_t x)
		554
		555	Returns the index of the least significant bit set in C<x> (or
		556	equivalently the number of bits set to 0 before the least significant bit
		557	set), starting from 0. If C<x> is 0 the result is undefined.
		558
		559	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		560
		561	For example:
		562
		563	ecb_ctz32 (3) = 0
		564	ecb_ctz32 (6) = 1
		565
		566	=item bool ecb_is_pot32 (uint32_t x)
		567
		568	=item bool ecb_is_pot64 (uint32_t x)
		569
		570	Return true iff C<x> is a power of two or C<x == 0>.
		571
		572	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		573
		574	=item int ecb_ld32 (uint32_t x)
		575
		576	=item int ecb_ld64 (uint64_t x)
		577
		578	Returns the index of the most significant bit set in C<x>, or the number
		579	of digits the number requires in binary (so that C<< 2**ld <= x <
		580	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		581	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		582	example to see how many bits a certain number requires to be encoded.
		583
		584	This function is similar to the "count leading zero bits" function, except
		585	that that one returns how many zero bits are "in front" of the number (in
		586	the given data type), while C<ecb_ld> returns how many bits the number
		587	itself requires.
		588
		589	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		590
42	int ecb_popcount32 (uint32_t x);	591	=item int ecb_popcount32 (uint32_t x)
		592
		593	=item int ecb_popcount64 (uint64_t x)
		594
		595	Returns the number of bits set to 1 in C<x>.
		596
		597	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		598
		599	For example:
		600
		601	ecb_popcount32 (7) = 3
		602	ecb_popcount32 (255) = 8
		603
		604	=item uint8_t ecb_bitrev8 (uint8_t x)
		605
		606	=item uint16_t ecb_bitrev16 (uint16_t x)
		607
43	uint32_t ecb_bswap32 (uint32_t x);	608	=item uint32_t ecb_bitrev32 (uint32_t x)
		609
		610	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		611	and so on.
		612
		613	Example:
		614
		615	ecb_bitrev8 (0xa7) = 0xea
		616	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		617
44	uint32_t ecb_bswap16 (uint32_t x);	618	=item uint32_t ecb_bswap16 (uint32_t x)
		619
		620	=item uint32_t ecb_bswap32 (uint32_t x)
		621
		622	=item uint64_t ecb_bswap64 (uint64_t x)
		623
		624	These functions return the value of the 16-bit (32-bit, 64-bit) value
		625	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		626	C<ecb_bswap32>).
		627
45	uint32_t ecb_rotr32 (uint32_t x, unsigned int count);	628	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		629
		630	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		631
46	uint32_t ecb_rotl32 (uint32_t x, unsigned int count);	632	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		633
		634	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		635
		636	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		637
		638	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
		639
		640	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
		641
		642	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
		643
		644	These two families of functions return the value of C<x> after rotating
		645	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		646	(C<ecb_rotl>).
		647
		648	Current GCC versions understand these functions and usually compile them
		649	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		650	x86).
		651
		652	=back
		653
		654	=head2 FLOATING POINT FIDDLING
		655
		656	=over 4
		657
		658	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		659
		660	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		661
		662	These functions each take an argument in the native C<float> or C<double>
		663	type and return the IEEE 754 bit representation of it.
		664
		665	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		666	will be the most significant bit, followed by exponent and mantissa.
		667
		668	This function should work even when the native floating point format isn't
		669	IEEE compliant, of course at a speed and code size penalty, and of course
		670	also within reasonable limits (it tries to convert NaNs, infinities and
		671	denormals, but will likely convert negative zero to positive zero).
		672
		673	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		674	be able to optimise away this function completely.
		675
		676	These functions can be helpful when serialising floats to the network - you
		677	can serialise the return value like a normal uint32_t/uint64_t.
		678
		679	Another use for these functions is to manipulate floating point values
		680	directly.
		681
		682	Silly example: toggle the sign bit of a float.
		683
		684	/* On gcc-4.7 on amd64, */
		685	/* this results in a single add instruction to toggle the bit, and 4 extra */
		686	/* instructions to move the float value to an integer register and back. */
		687
		688	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		689
		690	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		691
		692	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		693
		694	The reverse operation of the previos function - takes the bit representation
		695	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		696	or C<double> format.
		697
		698	This function should work even when the native floating point format isn't
		699	IEEE compliant, of course at a speed and code size penalty, and of course
		700	also within reasonable limits (it tries to convert normals and denormals,
		701	and might be lucky for infinities, and with extraordinary luck, also for
		702	negative zero).
		703
		704	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		705	be able to optimise away this function completely.
		706
		707	=back
47		708
48	=head2 ARITHMETIC	709	=head2 ARITHMETIC
49		710
		711	=over 4
		712
50	x = ecb_mod (m, n)	713	=item x = ecb_mod (m, n)
		714
		715	Returns C<m> modulo C<n>, which is the same as the positive remainder
		716	of the division operation between C<m> and C<n>, using floored
		717	division. Unlike the C remainder operator C<%>, this function ensures that
		718	the return value is always positive and that the two numbers I<m> and
		719	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		720	C<ecb_mod> implements the mathematical modulo operation, which is missing
		721	in the language.
		722
		723	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
		724	negatable, that is, both C<m> and C<-m> must be representable in its
		725	type (this typically excludes the minimum signed integer value, the same
		726	limitation as for C</> and C<%> in C).
		727
		728	Current GCC versions compile this into an efficient branchless sequence on
		729	almost all CPUs.
		730
		731	For example, when you want to rotate forward through the members of an
		732	array for increasing C<m> (which might be negative), then you should use
		733	C<ecb_mod>, as the C<%> operator might give either negative results, or
		734	change direction for negative values:
		735
		736	for (m = -100; m <= 100; ++m)
		737	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		738
		739	=item x = ecb_div_rd (val, div)
		740
		741	=item x = ecb_div_ru (val, div)
		742
		743	Returns C<val> divided by C<div> rounded down or up, respectively.
		744	C<val> and C<div> must have integer types and C<div> must be strictly
		745	positive. Note that these functions are implemented with macros in C
		746	and with function templates in C++.
		747
		748	=back
51		749
52	=head2 UTILITY	750	=head2 UTILITY
53		751
54	ecb_array_length (name)	752	=over 4
55		753
		754	=item element_count = ecb_array_length (name)
56		755
		756	Returns the number of elements in the array C<name>. For example:
		757
		758	int primes[] = { 2, 3, 5, 7, 11 };
		759	int sum = 0;
		760
		761	for (i = 0; i < ecb_array_length (primes); i++)
		762	sum += primes [i];
		763
		764	=back
		765
		766	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
		767
		768	These symbols need to be defined before including F<ecb.h> the first time.
		769
		770	=over 4
		771
		772	=item ECB_NO_THREADS
		773
		774	If F<ecb.h> is never used from multiple threads, then this symbol can
		775	be defined, in which case memory fences (and similar constructs) are
		776	completely removed, leading to more efficient code and fewer dependencies.
		777
		778	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		779
		780	=item ECB_NO_SMP
		781
		782	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		783	multiple threads, but never concurrently (e.g. if the system the program
		784	runs on has only a single CPU with a single core, no hyperthreading and so
		785	on), then this symbol can be defined, leading to more efficient code and
		786	fewer dependencies.
		787
		788	=item ECB_NO_LIBM
		789
		790	When defined to C<1>, do not export any functions that might introduce
		791	dependencies on the math library (usually called F<-lm>) - these are
		792	marked with [-UECB_NO_LIBM].
		793
		794	=back
		795
		796

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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 1.57 by root, Thu Oct 16 14:47:20 2014 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 1.57 by root, Thu Oct 16 14:47:20 2014 UTC