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Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC vs.
Revision 1.56 by root, Mon Jun 9 17:31:57 2014 UTC

…		…
3	=head2 ABOUT LIBECB	3	=head2 ABOUT LIBECB
4		4
5	Libecb is currently a simple header file that doesn't require any	5	Libecb is currently a simple header file that doesn't require any
6	configuration to use or include in your project.	6	configuration to use or include in your project.
7		7
8	It's part of the e-suite of libraries, other memembers of which include	8	It's part of the e-suite of libraries, other members of which include
9	libev and libeio.	9	libev and libeio.
10		10
11	Its homepage can be found here:	11	Its homepage can be found here:
12		12
13	http://software.schmorp.de/pkg/libecb	13	http://software.schmorp.de/pkg/libecb
14		14
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around GCC built-ins, together
16	with replacement functions for other compilers. In addition to this,	16	with replacement functions for other compilers. In addition to this,
17	it provides a number of other lowlevel C utilities, such endienness	17	it provides a number of other lowlevel C utilities, such as endianness
18	detection, byte swapping or bit rotations.	18	detection, byte swapping or bit rotations.
		19
		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.
19		23
20	More might come.	24	More might come.
21		25
22	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
23		27
…		…
27	#include <ecb.h>	31	#include <ecb.h>
28		32
29	The header should work fine for both C and C++ compilation, and gives you	33	The header should work fine for both C and C++ compilation, and gives you
30	all of F<inttypes.h> in addition to the ECB symbols.	34	all of F<inttypes.h> in addition to the ECB symbols.
31		35
32	There are currently no objetc files to link to - future versions might	36	There are currently no object files to link to - future versions might
33	come with an (optional) object code library to link against, to reduce	37	come with an (optional) object code library to link against, to reduce
34	code size or gain access to additional features.	38	code size or gain access to additional features.
35		39
36	It also currently includes everything from F<inttypes.h>.	40	It also currently includes everything from F<inttypes.h>.
37		41
…		…
50	only a generic name is used (C<expr>, C<cond>, C<value> and so on), then	54	only a generic name is used (C<expr>, C<cond>, C<value> and so on), then
51	the corresponding function relies on C to implement the correct types, and	55	the corresponding function relies on C to implement the correct types, and
52	is usually implemented as a macro. Specifically, a "bool" in this manual	56	is usually implemented as a macro. Specifically, a "bool" in this manual
53	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
54		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
		167
55	=head2 GCC ATTRIBUTES	168	=head2 GCC ATTRIBUTES
56		169
57	blabla where to put, what others	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;
58		185
59	=over 4	186	=over 4
60		187
61	=item ecb_attribute ((attrs...))	188	=item ecb_attribute ((attrs...))
62		189
63	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and	190	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
64	to nothing on other compilers, so the effect is that only GCC sees these.	191	nothing on other compilers, so the effect is that only GCC sees these.
		192
		193	Example: use the C<deprecated> attribute on a function.
		194
		195	ecb_attribute((__deprecated__)) void
		196	do_not_use_me_anymore (void);
65		197
66	=item ecb_unused	198	=item ecb_unused
67		199
68	Marks a function or a variable as "unused", which simply suppresses a	200	Marks a function or a variable as "unused", which simply suppresses a
69	warning by GCC when it detects it as unused. This is useful when you e.g.	201	warning by GCC when it detects it as unused. This is useful when you e.g.
70	declare a variable but do not always use it:	202	declare a variable but do not always use it:
71		203
		204	{
		205	int var ecb_unused;
		206
		207	#ifdef SOMECONDITION
		208	var = ...;
		209	return var;
		210	#else
		211	return 0;
		212	#endif
		213	}
		214
		215	=item ecb_deprecated
		216
		217	Similar to C<ecb_unused>, but marks a function, variable or type as
		218	deprecated. This makes some compilers warn when the type is used.
		219
		220	=item ecb_inline
		221
		222	This is not actually an attribute, but you use it like one. It expands
		223	either to C<static inline> or to just C<static>, if inline isn't
		224	supported. It should be used to declare functions that should be inlined,
		225	for code size or speed reasons.
		226
		227	Example: inline this function, it surely will reduce codesize.
		228
		229	ecb_inline int
		230	negmul (int a, int b)
72	{	231	{
73	int var ecb_unused;	232	return - (a * b);
74
75	#ifdef SOMECONDITION
76	var = ...;
77	return var;
78	#else
79	return 0;
80	#endif
81	}	233	}
82		234
83	=item ecb_noinline	235	=item ecb_noinline
84		236
85	Prevent a function from being inlined - it might be optimised away, but	237	Prevent a function from being inlined - it might be optimised away, but
86	not inlined into other functions. This is useful if you know your function	238	not inlined into other functions. This is useful if you know your function
87	is rarely called and large enough for inlining not to be helpful.	239	is rarely called and large enough for inlining not to be helpful.
88		240
89	=item ecb_noreturn	241	=item ecb_noreturn
90		242
		243	Marks a function as "not returning, ever". Some typical functions that
		244	don't return are C<exit> or C<abort> (which really works hard to not
		245	return), and now you can make your own:
		246
		247	ecb_noreturn void
		248	my_abort (const char *errline)
		249	{
		250	puts (errline);
		251	abort ();
		252	}
		253
		254	In this case, the compiler would probably be smart enough to deduce it on
		255	its own, so this is mainly useful for declarations.
		256
		257	=item ecb_restrict
		258
		259	Expands to the C<restrict> keyword or equivalent on compilers that support
		260	them, and to nothing on others. Must be specified on a pointer type or
		261	an array index to indicate that the memory doesn't alias with any other
		262	restricted pointer in the same scope.
		263
		264	Example: multiply a vector, and allow the compiler to parallelise the
		265	loop, because it knows it doesn't overwrite input values.
		266
		267	void
		268	multiply (float *ecb_restrict src,
		269	float *ecb_restrict dst,
		270	int len, float factor)
		271	{
		272	int i;
		273
		274	for (i = 0; i < len; ++i)
		275	dst [i] = src [i] * factor;
		276	}
		277
91	=item ecb_const	278	=item ecb_const
92		279
		280	Declares that the function only depends on the values of its arguments,
		281	much like a mathematical function. It specifically does not read or write
		282	any memory any arguments might point to, global variables, or call any
		283	non-const functions. It also must not have any side effects.
		284
		285	Such a function can be optimised much more aggressively by the compiler -
		286	for example, multiple calls with the same arguments can be optimised into
		287	a single call, which wouldn't be possible if the compiler would have to
		288	expect any side effects.
		289
		290	It is best suited for functions in the sense of mathematical functions,
		291	such as a function returning the square root of its input argument.
		292
		293	Not suited would be a function that calculates the hash of some memory
		294	area you pass in, prints some messages or looks at a global variable to
		295	decide on rounding.
		296
		297	See C<ecb_pure> for a slightly less restrictive class of functions.
		298
93	=item ecb_pure	299	=item ecb_pure
94		300
		301	Similar to C<ecb_const>, declares a function that has no side
		302	effects. Unlike C<ecb_const>, the function is allowed to examine global
		303	variables and any other memory areas (such as the ones passed to it via
		304	pointers).
		305
		306	While these functions cannot be optimised as aggressively as C<ecb_const>
		307	functions, they can still be optimised away in many occasions, and the
		308	compiler has more freedom in moving calls to them around.
		309
		310	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		311	function that calculates the MD5 sum of some input and updates some MD5
		312	state passed as argument would I<NOT> be pure, however, as it would modify
		313	some memory area that is not the return value.
		314
95	=item ecb_hot	315	=item ecb_hot
96		316
		317	This declares a function as "hot" with regards to the cache - the function
		318	is used so often, that it is very beneficial to keep it in the cache if
		319	possible.
		320
		321	The compiler reacts by trying to place hot functions near to each other in
		322	memory.
		323
		324	Whether a function is hot or not often depends on the whole program,
		325	and less on the function itself. C<ecb_cold> is likely more useful in
		326	practise.
		327
97	=item ecb_cold	328	=item ecb_cold
98		329
		330	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		331	the cache, or in other words, this function is not called often, or not at
		332	speed-critical times, and keeping it in the cache might be a waste of said
		333	cache.
		334
		335	In addition to placing cold functions together (or at least away from hot
		336	functions), this knowledge can be used in other ways, for example, the
		337	function will be optimised for size, as opposed to speed, and codepaths
		338	leading to calls to those functions can automatically be marked as if
		339	C<ecb_expect_false> had been used to reach them.
		340
		341	Good examples for such functions would be error reporting functions, or
		342	functions only called in exceptional or rare cases.
		343
99	=item ecb_artificial	344	=item ecb_artificial
		345
		346	Declares the function as "artificial", in this case meaning that this
		347	function is not really meant to be a function, but more like an accessor
		348	- many methods in C++ classes are mere accessor functions, and having a
		349	crash reported in such a method, or single-stepping through them, is not
		350	usually so helpful, especially when it's inlined to just a few instructions.
		351
		352	Marking them as artificial will instruct the debugger about just this,
		353	leading to happier debugging and thus happier lives.
		354
		355	Example: in some kind of smart-pointer class, mark the pointer accessor as
		356	artificial, so that the whole class acts more like a pointer and less like
		357	some C++ abstraction monster.
		358
		359	template<typename T>
		360	struct my_smart_ptr
		361	{
		362	T *value;
		363
		364	ecb_artificial
		365	operator T *()
		366	{
		367	return value;
		368	}
		369	};
100		370
101	=back	371	=back
102		372
103	=head2 OPTIMISATION HINTS	373	=head2 OPTIMISATION HINTS
104		374
…		…
136		406
137	Evaluates C<expr> and returns it. In addition, it tells the compiler that	407	Evaluates C<expr> and returns it. In addition, it tells the compiler that
138	the C<expr> evaluates to C<value> a lot, which can be used for static	408	the C<expr> evaluates to C<value> a lot, which can be used for static
139	branch optimisations.	409	branch optimisations.
140		410
141	Usually, you want to use the more intuitive C<ecb_likely> and	411	Usually, you want to use the more intuitive C<ecb_expect_true> and
142	C<ecb_unlikely> functions instead.	412	C<ecb_expect_false> functions instead.
143		413
144	=item bool ecb_likely (bool)	414	=item bool ecb_expect_true (cond)
145		415
146	=item bool ecb_unlikely (bool)	416	=item bool ecb_expect_false (cond)
147		417
148	These two functions expect a expression that is true or false and return	418	These two functions expect a expression that is true or false and return
149	C<1> or C<0>, respectively, so when used in the condition of an C<if> or	419	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
150	other conditional statement, it will not change the program:	420	other conditional statement, it will not change the program:
151		421
152	/* these two do the same thing */	422	/* these two do the same thing */
153	if (some_condition) ...;	423	if (some_condition) ...;
154	if (ecb_likely (some_condition)) ...;	424	if (ecb_expect_true (some_condition)) ...;
155		425
156	However, by using C<ecb_likely>, you tell the compiler that the condition	426	However, by using C<ecb_expect_true>, you tell the compiler that the
157	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be	427	condition is likely to be true (and for C<ecb_expect_false>, that it is
158	true).	428	unlikely to be true).
159		429
160	For example, when you check for a null pointer and expect this to be a	430	For example, when you check for a null pointer and expect this to be a
161	rare, exceptional, case, then use C<ecb_unlikely>:	431	rare, exceptional, case, then use C<ecb_expect_false>:
162		432
163	void my_free (void *ptr)	433	void my_free (void *ptr)
164	{	434	{
165	if (ecb_unlikely (ptr == 0))	435	if (ecb_expect_false (ptr == 0))
166	return;	436	return;
167	}	437	}
168		438
169	Consequent use of these functions to mark away exceptional cases or to	439	Consequent use of these functions to mark away exceptional cases or to
170	tell the compiler what the hot path through a function is can increase	440	tell the compiler what the hot path through a function is can increase
171	performance considerably.	441	performance considerably.
		442
		443	You might know these functions under the name C<likely> and C<unlikely>
		444	- while these are common aliases, we find that the expect name is easier
		445	to understand when quickly skimming code. If you wish, you can use
		446	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		447	C<ecb_expect_false> - these are simply aliases.
172		448
173	A very good example is in a function that reserves more space for some	449	A very good example is in a function that reserves more space for some
174	memory block (for example, inside an implementation of a string stream) -	450	memory block (for example, inside an implementation of a string stream) -
175	each time something is added, you have to check for a buffer overrun, but	451	each time something is added, you have to check for a buffer overrun, but
176	you expect that most checks will turn out to be false:	452	you expect that most checks will turn out to be false:
177		453
178	/* make sure we have "size" extra room in our buffer */	454	/* make sure we have "size" extra room in our buffer */
179	ecb_inline void	455	ecb_inline void
180	reserve (int size)	456	reserve (int size)
181	{	457	{
182	if (ecb_unlikely (current + size > end))	458	if (ecb_expect_false (current + size > end))
183	real_reserve_method (size); /* presumably noinline */	459	real_reserve_method (size); /* presumably noinline */
184	}	460	}
185		461
186	=item bool ecb_assume (cond)	462	=item bool ecb_assume (cond)
187		463
…		…
190		466
191	This can be used to teach the compiler about invariants or other	467	This can be used to teach the compiler about invariants or other
192	conditions that might improve code generation, but which are impossible to	468	conditions that might improve code generation, but which are impossible to
193	deduce form the code itself.	469	deduce form the code itself.
194		470
195	For example, the example reservation function from the C<ecb_unlikely>	471	For example, the example reservation function from the C<ecb_expect_false>
196	description could be written thus (only C<ecb_assume> was added):	472	description could be written thus (only C<ecb_assume> was added):
197		473
198	ecb_inline void	474	ecb_inline void
199	reserve (int size)	475	reserve (int size)
200	{	476	{
201	if (ecb_unlikely (current + size > end))	477	if (ecb_expect_false (current + size > end))
202	real_reserve_method (size); /* presumably noinline */	478	real_reserve_method (size); /* presumably noinline */
203		479
204	ecb_assume (current + size <= end);	480	ecb_assume (current + size <= end);
205	}	481	}
206		482
…		…
255	After processing the node, (part of) the next node might already be in	531	After processing the node, (part of) the next node might already be in
256	cache.	532	cache.
257		533
258	=back	534	=back
259		535
260	=head2 BIT FIDDLING / BITSTUFFS	536	=head2 BIT FIDDLING / BIT WIZARDRY
261		537
262	=over 4	538	=over 4
263		539
264	=item bool ecb_big_endian ()	540	=item bool ecb_big_endian ()
265		541
…		…
267		543
268	These two functions return true if the byte order is big endian	544	These two functions return true if the byte order is big endian
269	(most-significant byte first) or little endian (least-significant byte	545	(most-significant byte first) or little endian (least-significant byte
270	first) respectively.	546	first) respectively.
271		547
		548	On systems that are neither, their return values are unspecified.
		549
272	=item int ecb_ctz32 (uint32_t x)	550	=item int ecb_ctz32 (uint32_t x)
273		551
		552	=item int ecb_ctz64 (uint64_t x)
		553
274	Returns the index of the least significant bit set in C<x> (or	554	Returns the index of the least significant bit set in C<x> (or
275	equivalently the number of bits set to 0 before the least significant	555	equivalently the number of bits set to 0 before the least significant bit
276	bit set), starting from 0. If C<x> is 0 the result is undefined. A	556	set), starting from 0. If C<x> is 0 the result is undefined.
277	common use case is to compute the integer binary logarithm, i.e.,
278	floor(log2(n)). For example:
279		557
		558	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		559
		560	For example:
		561
280	ecb_ctz32(3) = 0	562	ecb_ctz32 (3) = 0
281	ecb_ctz32(6) = 1	563	ecb_ctz32 (6) = 1
		564
		565	=item bool ecb_is_pot32 (uint32_t x)
		566
		567	=item bool ecb_is_pot64 (uint32_t x)
		568
		569	Return true iff C<x> is a power of two or C<x == 0>.
		570
		571	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		572
		573	=item int ecb_ld32 (uint32_t x)
		574
		575	=item int ecb_ld64 (uint64_t x)
		576
		577	Returns the index of the most significant bit set in C<x>, or the number
		578	of digits the number requires in binary (so that C<< 2**ld <= x <
		579	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		580	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		581	example to see how many bits a certain number requires to be encoded.
		582
		583	This function is similar to the "count leading zero bits" function, except
		584	that that one returns how many zero bits are "in front" of the number (in
		585	the given data type), while C<ecb_ld> returns how many bits the number
		586	itself requires.
		587
		588	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
282		589
283	=item int ecb_popcount32 (uint32_t x)	590	=item int ecb_popcount32 (uint32_t x)
284		591
		592	=item int ecb_popcount64 (uint64_t x)
		593
285	Returns the number of bits set to 1 in C<x>. For example:	594	Returns the number of bits set to 1 in C<x>.
286		595
		596	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		597
		598	For example:
		599
287	ecb_popcount32(7) = 3	600	ecb_popcount32 (7) = 3
288	ecb_popcount32(255) = 8	601	ecb_popcount32 (255) = 8
		602
		603	=item uint8_t ecb_bitrev8 (uint8_t x)
		604
		605	=item uint16_t ecb_bitrev16 (uint16_t x)
		606
		607	=item uint32_t ecb_bitrev32 (uint32_t x)
		608
		609	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		610	and so on.
		611
		612	Example:
		613
		614	ecb_bitrev8 (0xa7) = 0xea
		615	ecb_bitrev32 (0xffcc4411) = 0x882233ff
289		616
290	=item uint32_t ecb_bswap16 (uint32_t x)	617	=item uint32_t ecb_bswap16 (uint32_t x)
291		618
292	=item uint32_t ecb_bswap32 (uint32_t x)	619	=item uint32_t ecb_bswap32 (uint32_t x)
293		620
		621	=item uint64_t ecb_bswap64 (uint64_t x)
		622
294	These two functions return the value of the 16-bit (32-bit) variable	623	These functions return the value of the 16-bit (32-bit, 64-bit) value
295	C<x> after reversing the order of bytes.	624	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		625	C<ecb_bswap32>).
		626
		627	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		628
		629	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		630
		631	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		632
		633	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		634
		635	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		636
		637	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
296		638
297	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	639	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
298		640
299	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	641	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
300		642
301	These two functions return the value of C<x> after shifting all the bits	643	These two families of functions return the value of C<x> after rotating
302	by C<count> positions to the right or left respectively.	644	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		645	(C<ecb_rotl>).
		646
		647	Current GCC versions understand these functions and usually compile them
		648	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		649	x86).
303		650
304	=back	651	=back
305		652
		653	=head2 FLOATING POINT FIDDLING
		654
		655	=over 4
		656
		657	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		658
		659	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		660
		661	These functions each take an argument in the native C<float> or C<double>
		662	type and return the IEEE 754 bit representation of it.
		663
		664	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		665	will be the most significant bit, followed by exponent and mantissa.
		666
		667	This function should work even when the native floating point format isn't
		668	IEEE compliant, of course at a speed and code size penalty, and of course
		669	also within reasonable limits (it tries to convert NaNs, infinities and
		670	denormals, but will likely convert negative zero to positive zero).
		671
		672	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		673	be able to optimise away this function completely.
		674
		675	These functions can be helpful when serialising floats to the network - you
		676	can serialise the return value like a normal uint32_t/uint64_t.
		677
		678	Another use for these functions is to manipulate floating point values
		679	directly.
		680
		681	Silly example: toggle the sign bit of a float.
		682
		683	/* On gcc-4.7 on amd64, */
		684	/* this results in a single add instruction to toggle the bit, and 4 extra */
		685	/* instructions to move the float value to an integer register and back. */
		686
		687	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		688
		689	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		690
		691	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		692
		693	The reverse operation of the previos function - takes the bit representation
		694	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		695	or C<double> format.
		696
		697	This function should work even when the native floating point format isn't
		698	IEEE compliant, of course at a speed and code size penalty, and of course
		699	also within reasonable limits (it tries to convert normals and denormals,
		700	and might be lucky for infinities, and with extraordinary luck, also for
		701	negative zero).
		702
		703	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		704	be able to optimise away this function completely.
		705
		706	=back
		707
306	=head2 ARITHMETIC	708	=head2 ARITHMETIC
307		709
308	=over 4	710	=over 4
309		711
310	=item x = ecb_mod (m, n)	712	=item x = ecb_mod (m, n)
311		713
312	Returns the positive remainder of the modulo operation between C<m> and	714	Returns C<m> modulo C<n>, which is the same as the positive remainder
		715	of the division operation between C<m> and C<n>, using floored
313	C<n>. Unlike the C moduloe operator C<%>, this function ensures that the	716	division. Unlike the C remainder operator C<%>, this function ensures that
314	return value is always positive).	717	the return value is always positive and that the two numbers I<m> and
		718	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		719	C<ecb_mod> implements the mathematical modulo operation, which is missing
		720	in the language.
315		721
316	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	722	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
317	negatable, that is, both C<m> and C<-m> must be representable in its	723	negatable, that is, both C<m> and C<-m> must be representable in its
318	type.	724	type (this typically excludes the minimum signed integer value, the same
		725	limitation as for C</> and C<%> in C).
		726
		727	Current GCC versions compile this into an efficient branchless sequence on
		728	almost all CPUs.
		729
		730	For example, when you want to rotate forward through the members of an
		731	array for increasing C<m> (which might be negative), then you should use
		732	C<ecb_mod>, as the C<%> operator might give either negative results, or
		733	change direction for negative values:
		734
		735	for (m = -100; m <= 100; ++m)
		736	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		737
		738	=item x = ecb_div_rd (val, div)
		739
		740	=item x = ecb_div_ru (val, div)
		741
		742	Returns C<val> divided by C<div> rounded down or up, respectively.
		743	C<val> and C<div> must have integer types and C<div> must be strictly
		744	positive. Note that these functions are implemented with macros in C
		745	and with function templates in C++.
319		746
320	=back	747	=back
321		748
322	=head2 UTILITY	749	=head2 UTILITY
323		750
324	=over 4	751	=over 4
325		752
326	=item element_count = ecb_array_length (name) [MACRO]	753	=item element_count = ecb_array_length (name)
327		754
328	Returns the number of elements in the array C<name>. For example:	755	Returns the number of elements in the array C<name>. For example:
329		756
330	int primes[] = { 2, 3, 5, 7, 11 };	757	int primes[] = { 2, 3, 5, 7, 11 };
331	int sum = 0;	758	int sum = 0;
…		…
333	for (i = 0; i < ecb_array_length (primes); i++)	760	for (i = 0; i < ecb_array_length (primes); i++)
334	sum += primes [i];	761	sum += primes [i];
335		762
336	=back	763	=back
337		764
		765	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
338		766
		767	These symbols need to be defined before including F<ecb.h> the first time.
		768
		769	=over 4
		770
		771	=item ECB_NO_THREADS
		772
		773	If F<ecb.h> is never used from multiple threads, then this symbol can
		774	be defined, in which case memory fences (and similar constructs) are
		775	completely removed, leading to more efficient code and fewer dependencies.
		776
		777	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		778
		779	=item ECB_NO_SMP
		780
		781	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		782	multiple threads, but never concurrently (e.g. if the system the program
		783	runs on has only a single CPU with a single core, no hyperthreading and so
		784	on), then this symbol can be defined, leading to more efficient code and
		785	fewer dependencies.
		786
		787	=item ECB_NO_LIBM
		788
		789	When defined to C<1>, do not export any functions that might introduce
		790	dependencies on the math library (usually called F<-lm>) - these are
		791	marked with [-UECB_NO_LIBM].
		792
		793	=back
		794
		795

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Comparing libecb/ecb.pod (file contents): Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC vs. Revision 1.56 by root, Mon Jun 9 17:31:57 2014 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC vs.
Revision 1.56 by root, Mon Jun 9 17:31:57 2014 UTC