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Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC vs.
Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 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
55	=head2 GCC ATTRIBUTES	59	=head2 TYPES / TYPE SUPPORT
56		60
57	blabla where to put, what others	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).
58		78
59	=over 4	79	=over 4
60		80
61	=item ecb_attribute ((attrs...))	81	=item ECB_C
62		82
63	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and	83	True if the implementation defines the C<__STDC__> macro to a true value,
64	to nothing on other compilers, so the effect is that only GCC sees these.	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
		168	=head2 ATTRIBUTES
		169
		170	A major part of libecb deals with additional attributes that can be
		171	assigned to functions, variables and sometimes even types - much like
		172	C<const> or C<volatile> in C. They are implemented using either GCC
		173	attributes or other compiler/language specific features. Attributes
		174	declarations must be put before the whole declaration:
		175
		176	ecb_const int mysqrt (int a);
		177	ecb_unused int i;
		178
		179	=over 4
65		180
66	=item ecb_unused	181	=item ecb_unused
67		182
68	Marks a function or a variable as "unused", which simply suppresses a	183	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.	184	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:	185	declare a variable but do not always use it:
71		186
		187	{
		188	ecb_unused int var;
		189
		190	#ifdef SOMECONDITION
		191	var = ...;
		192	return var;
		193	#else
		194	return 0;
		195	#endif
		196	}
		197
		198	=item ecb_deprecated
		199
		200	Similar to C<ecb_unused>, but marks a function, variable or type as
		201	deprecated. This makes some compilers warn when the type is used.
		202
		203	=item ecb_inline
		204
		205	Expands either to C<static inline> or to just C<static>, if inline
		206	isn't supported. It should be used to declare functions that should be
		207	inlined, for code size or speed reasons.
		208
		209	Example: inline this function, it surely will reduce codesize.
		210
		211	ecb_inline int
		212	negmul (int a, int b)
72	{	213	{
73	int var ecb_unused;	214	return - (a * b);
74
75	#ifdef SOMECONDITION
76	var = ...;
77	return var;
78	#else
79	return 0;
80	#endif
81	}	215	}
82		216
83	=item ecb_noinline	217	=item ecb_noinline
84		218
85	Prevent a function from being inlined - it might be optimised away, but	219	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	220	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.	221	is rarely called and large enough for inlining not to be helpful.
88		222
89	=item ecb_noreturn	223	=item ecb_noreturn
90		224
		225	Marks a function as "not returning, ever". Some typical functions that
		226	don't return are C<exit> or C<abort> (which really works hard to not
		227	return), and now you can make your own:
		228
		229	ecb_noreturn void
		230	my_abort (const char *errline)
		231	{
		232	puts (errline);
		233	abort ();
		234	}
		235
		236	In this case, the compiler would probably be smart enough to deduce it on
		237	its own, so this is mainly useful for declarations.
		238
		239	=item ecb_restrict
		240
		241	Expands to the C<restrict> keyword or equivalent on compilers that support
		242	them, and to nothing on others. Must be specified on a pointer type or
		243	an array index to indicate that the memory doesn't alias with any other
		244	restricted pointer in the same scope.
		245
		246	Example: multiply a vector, and allow the compiler to parallelise the
		247	loop, because it knows it doesn't overwrite input values.
		248
		249	void
		250	multiply (ecb_restrict float *src,
		251	ecb_restrict float *dst,
		252	int len, float factor)
		253	{
		254	int i;
		255
		256	for (i = 0; i < len; ++i)
		257	dst [i] = src [i] * factor;
		258	}
		259
91	=item ecb_const	260	=item ecb_const
92		261
		262	Declares that the function only depends on the values of its arguments,
		263	much like a mathematical function. It specifically does not read or write
		264	any memory any arguments might point to, global variables, or call any
		265	non-const functions. It also must not have any side effects.
		266
		267	Such a function can be optimised much more aggressively by the compiler -
		268	for example, multiple calls with the same arguments can be optimised into
		269	a single call, which wouldn't be possible if the compiler would have to
		270	expect any side effects.
		271
		272	It is best suited for functions in the sense of mathematical functions,
		273	such as a function returning the square root of its input argument.
		274
		275	Not suited would be a function that calculates the hash of some memory
		276	area you pass in, prints some messages or looks at a global variable to
		277	decide on rounding.
		278
		279	See C<ecb_pure> for a slightly less restrictive class of functions.
		280
93	=item ecb_pure	281	=item ecb_pure
94		282
		283	Similar to C<ecb_const>, declares a function that has no side
		284	effects. Unlike C<ecb_const>, the function is allowed to examine global
		285	variables and any other memory areas (such as the ones passed to it via
		286	pointers).
		287
		288	While these functions cannot be optimised as aggressively as C<ecb_const>
		289	functions, they can still be optimised away in many occasions, and the
		290	compiler has more freedom in moving calls to them around.
		291
		292	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		293	function that calculates the MD5 sum of some input and updates some MD5
		294	state passed as argument would I<NOT> be pure, however, as it would modify
		295	some memory area that is not the return value.
		296
95	=item ecb_hot	297	=item ecb_hot
96		298
		299	This declares a function as "hot" with regards to the cache - the function
		300	is used so often, that it is very beneficial to keep it in the cache if
		301	possible.
		302
		303	The compiler reacts by trying to place hot functions near to each other in
		304	memory.
		305
		306	Whether a function is hot or not often depends on the whole program,
		307	and less on the function itself. C<ecb_cold> is likely more useful in
		308	practise.
		309
97	=item ecb_cold	310	=item ecb_cold
98		311
		312	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		313	the cache, or in other words, this function is not called often, or not at
		314	speed-critical times, and keeping it in the cache might be a waste of said
		315	cache.
		316
		317	In addition to placing cold functions together (or at least away from hot
		318	functions), this knowledge can be used in other ways, for example, the
		319	function will be optimised for size, as opposed to speed, and codepaths
		320	leading to calls to those functions can automatically be marked as if
		321	C<ecb_expect_false> had been used to reach them.
		322
		323	Good examples for such functions would be error reporting functions, or
		324	functions only called in exceptional or rare cases.
		325
99	=item ecb_artificial	326	=item ecb_artificial
100		327
		328	Declares the function as "artificial", in this case meaning that this
		329	function is not really meant to be a function, but more like an accessor
		330	- many methods in C++ classes are mere accessor functions, and having a
		331	crash reported in such a method, or single-stepping through them, is not
		332	usually so helpful, especially when it's inlined to just a few instructions.
		333
		334	Marking them as artificial will instruct the debugger about just this,
		335	leading to happier debugging and thus happier lives.
		336
		337	Example: in some kind of smart-pointer class, mark the pointer accessor as
		338	artificial, so that the whole class acts more like a pointer and less like
		339	some C++ abstraction monster.
		340
		341	template<typename T>
		342	struct my_smart_ptr
		343	{
		344	T *value;
		345
		346	ecb_artificial
		347	operator T *()
		348	{
		349	return value;
		350	}
		351	};
		352
101	=back	353	=back
102		354
103	=head2 OPTIMISATION HINTS	355	=head2 OPTIMISATION HINTS
104		356
105	=over 4	357	=over 4
106		358
107	=item bool ecb_is_constant(expr)	359	=item bool ecb_is_constant (expr)
108		360
109	Returns true iff the expression can be deduced to be a compile-time	361	Returns true iff the expression can be deduced to be a compile-time
110	constant, and false otherwise.	362	constant, and false otherwise.
111		363
112	For example, when you have a C<rndm16> function that returns a 16 bit	364	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
136		388
137	Evaluates C<expr> and returns it. In addition, it tells the compiler that	389	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	390	the C<expr> evaluates to C<value> a lot, which can be used for static
139	branch optimisations.	391	branch optimisations.
140		392
141	Usually, you want to use the more intuitive C<ecb_likely> and	393	Usually, you want to use the more intuitive C<ecb_expect_true> and
142	C<ecb_unlikely> functions instead.	394	C<ecb_expect_false> functions instead.
143		395
144	=item bool ecb_likely (bool)	396	=item bool ecb_expect_true (cond)
145		397
146	=item bool ecb_unlikely (bool)	398	=item bool ecb_expect_false (cond)
147		399
148	These two functions expect a expression that is true or false and return	400	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	401	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:	402	other conditional statement, it will not change the program:
151		403
152	/* these two do the same thing */	404	/* these two do the same thing */
153	if (some_condition) ...;	405	if (some_condition) ...;
154	if (ecb_likely (some_condition)) ...;	406	if (ecb_expect_true (some_condition)) ...;
155		407
156	However, by using C<ecb_likely>, you tell the compiler that the condition	408	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	409	condition is likely to be true (and for C<ecb_expect_false>, that it is
158	true).	410	unlikely to be true).
159		411
160	For example, when you check for a null pointer and expect this to be a	412	For example, when you check for a null pointer and expect this to be a
161	rare, exceptional, case, then use C<ecb_unlikely>:	413	rare, exceptional, case, then use C<ecb_expect_false>:
162		414
163	void my_free (void *ptr)	415	void my_free (void *ptr)
164	{	416	{
165	if (ecb_unlikely (ptr == 0))	417	if (ecb_expect_false (ptr == 0))
166	return;	418	return;
167	}	419	}
168		420
169	Consequent use of these functions to mark away exceptional cases or to	421	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	422	tell the compiler what the hot path through a function is can increase
171	performance considerably.	423	performance considerably.
		424
		425	You might know these functions under the name C<likely> and C<unlikely>
		426	- while these are common aliases, we find that the expect name is easier
		427	to understand when quickly skimming code. If you wish, you can use
		428	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		429	C<ecb_expect_false> - these are simply aliases.
172		430
173	A very good example is in a function that reserves more space for some	431	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) -	432	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	433	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:	434	you expect that most checks will turn out to be false:
177		435
178	/* make sure we have "size" extra room in our buffer */	436	/* make sure we have "size" extra room in our buffer */
179	ecb_inline void	437	ecb_inline void
180	reserve (int size)	438	reserve (int size)
181	{	439	{
182	if (ecb_unlikely (current + size > end))	440	if (ecb_expect_false (current + size > end))
183	real_reserve_method (size); /* presumably noinline */	441	real_reserve_method (size); /* presumably noinline */
184	}	442	}
185		443
186	=item bool ecb_assume (cond)	444	=item bool ecb_assume (cond)
187		445
…		…
190		448
191	This can be used to teach the compiler about invariants or other	449	This can be used to teach the compiler about invariants or other
192	conditions that might improve code generation, but which are impossible to	450	conditions that might improve code generation, but which are impossible to
193	deduce form the code itself.	451	deduce form the code itself.
194		452
195	For example, the example reservation function from the C<ecb_unlikely>	453	For example, the example reservation function from the C<ecb_expect_false>
196	description could be written thus (only C<ecb_assume> was added):	454	description could be written thus (only C<ecb_assume> was added):
197		455
198	ecb_inline void	456	ecb_inline void
199	reserve (int size)	457	reserve (int size)
200	{	458	{
201	if (ecb_unlikely (current + size > end))	459	if (ecb_expect_false (current + size > end))
202	real_reserve_method (size); /* presumably noinline */	460	real_reserve_method (size); /* presumably noinline */
203		461
204	ecb_assume (current + size <= end);	462	ecb_assume (current + size <= end);
205	}	463	}
206		464
…		…
255	After processing the node, (part of) the next node might already be in	513	After processing the node, (part of) the next node might already be in
256	cache.	514	cache.
257		515
258	=back	516	=back
259		517
260	=head2 BIT FIDDLING / BITSTUFFS	518	=head2 BIT FIDDLING / BIT WIZARDRY
261		519
262	=over 4	520	=over 4
263		521
264	=item bool ecb_big_endian ()	522	=item bool ecb_big_endian ()
265		523
…		…
267		525
268	These two functions return true if the byte order is big endian	526	These two functions return true if the byte order is big endian
269	(most-significant byte first) or little endian (least-significant byte	527	(most-significant byte first) or little endian (least-significant byte
270	first) respectively.	528	first) respectively.
271		529
		530	On systems that are neither, their return values are unspecified.
		531
272	=item int ecb_ctz32 (uint32_t x)	532	=item int ecb_ctz32 (uint32_t x)
273		533
		534	=item int ecb_ctz64 (uint64_t x)
		535
274	Returns the index of the least significant bit set in C<x> (or	536	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	537	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	538	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		539
		540	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		541
		542	For example:
		543
280	ecb_ctz32(3) = 0	544	ecb_ctz32 (3) = 0
281	ecb_ctz32(6) = 1	545	ecb_ctz32 (6) = 1
		546
		547	=item bool ecb_is_pot32 (uint32_t x)
		548
		549	=item bool ecb_is_pot64 (uint32_t x)
		550
		551	Return true iff C<x> is a power of two or C<x == 0>.
		552
		553	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		554
		555	=item int ecb_ld32 (uint32_t x)
		556
		557	=item int ecb_ld64 (uint64_t x)
		558
		559	Returns the index of the most significant bit set in C<x>, or the number
		560	of digits the number requires in binary (so that C<< 2**ld <= x <
		561	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		562	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		563	example to see how many bits a certain number requires to be encoded.
		564
		565	This function is similar to the "count leading zero bits" function, except
		566	that that one returns how many zero bits are "in front" of the number (in
		567	the given data type), while C<ecb_ld> returns how many bits the number
		568	itself requires.
		569
		570	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
282		571
283	=item int ecb_popcount32 (uint32_t x)	572	=item int ecb_popcount32 (uint32_t x)
284		573
		574	=item int ecb_popcount64 (uint64_t x)
		575
285	Returns the number of bits set to 1 in C<x>. For example:	576	Returns the number of bits set to 1 in C<x>.
286		577
		578	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		579
		580	For example:
		581
287	ecb_popcount32(7) = 3	582	ecb_popcount32 (7) = 3
288	ecb_popcount32(255) = 8	583	ecb_popcount32 (255) = 8
		584
		585	=item uint8_t ecb_bitrev8 (uint8_t x)
		586
		587	=item uint16_t ecb_bitrev16 (uint16_t x)
		588
		589	=item uint32_t ecb_bitrev32 (uint32_t x)
		590
		591	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		592	and so on.
		593
		594	Example:
		595
		596	ecb_bitrev8 (0xa7) = 0xea
		597	ecb_bitrev32 (0xffcc4411) = 0x882233ff
289		598
290	=item uint32_t ecb_bswap16 (uint32_t x)	599	=item uint32_t ecb_bswap16 (uint32_t x)
291		600
292	=item uint32_t ecb_bswap32 (uint32_t x)	601	=item uint32_t ecb_bswap32 (uint32_t x)
293		602
		603	=item uint64_t ecb_bswap64 (uint64_t x)
		604
294	These two functions return the value of the 16-bit (32-bit) variable	605	These functions return the value of the 16-bit (32-bit, 64-bit) value
295	C<x> after reversing the order of bytes.	606	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		607	C<ecb_bswap32>).
		608
		609	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		610
		611	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		612
		613	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		614
		615	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		616
		617	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		618
		619	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
296		620
297	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	621	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
298		622
299	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	623	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
300		624
301	These two functions return the value of C<x> after shifting all the bits	625	These two families of functions return the value of C<x> after rotating
302	by C<count> positions to the right or left respectively.	626	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		627	(C<ecb_rotl>).
		628
		629	Current GCC versions understand these functions and usually compile them
		630	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		631	x86).
303		632
304	=back	633	=back
305		634
		635	=head2 FLOATING POINT FIDDLING
		636
		637	=over 4
		638
		639	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		640
		641	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		642
		643	These functions each take an argument in the native C<float> or C<double>
		644	type and return the IEEE 754 bit representation of it.
		645
		646	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		647	will be the most significant bit, followed by exponent and mantissa.
		648
		649	This function should work even when the native floating point format isn't
		650	IEEE compliant, of course at a speed and code size penalty, and of course
		651	also within reasonable limits (it tries to convert NaNs, infinities and
		652	denormals, but will likely convert negative zero to positive zero).
		653
		654	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		655	be able to optimise away this function completely.
		656
		657	These functions can be helpful when serialising floats to the network - you
		658	can serialise the return value like a normal uint32_t/uint64_t.
		659
		660	Another use for these functions is to manipulate floating point values
		661	directly.
		662
		663	Silly example: toggle the sign bit of a float.
		664
		665	/* On gcc-4.7 on amd64, */
		666	/* this results in a single add instruction to toggle the bit, and 4 extra */
		667	/* instructions to move the float value to an integer register and back. */
		668
		669	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		670
		671	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		672
		673	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		674
		675	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		676
		677	The reverse operation of the previous function - takes the bit
		678	representation of an IEEE binary16, binary32 or binary64 number and
		679	converts it to the native C<float> or C<double> format.
		680
		681	This function should work even when the native floating point format isn't
		682	IEEE compliant, of course at a speed and code size penalty, and of course
		683	also within reasonable limits (it tries to convert normals and denormals,
		684	and might be lucky for infinities, and with extraordinary luck, also for
		685	negative zero).
		686
		687	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		688	be able to optimise away this function completely.
		689
		690	=back
		691
306	=head2 ARITHMETIC	692	=head2 ARITHMETIC
307		693
308	=over 4	694	=over 4
309		695
310	=item x = ecb_mod (m, n)	696	=item x = ecb_mod (m, n)
311		697
312	Returns the positive remainder of the modulo operation between C<m> and	698	Returns C<m> modulo C<n>, which is the same as the positive remainder
		699	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	700	division. Unlike the C remainder operator C<%>, this function ensures that
314	return value is always positive).	701	the return value is always positive and that the two numbers I<m> and
		702	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		703	C<ecb_mod> implements the mathematical modulo operation, which is missing
		704	in the language.
315		705
316	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	706	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	707	negatable, that is, both C<m> and C<-m> must be representable in its
318	type.	708	type (this typically excludes the minimum signed integer value, the same
		709	limitation as for C</> and C<%> in C).
		710
		711	Current GCC versions compile this into an efficient branchless sequence on
		712	almost all CPUs.
		713
		714	For example, when you want to rotate forward through the members of an
		715	array for increasing C<m> (which might be negative), then you should use
		716	C<ecb_mod>, as the C<%> operator might give either negative results, or
		717	change direction for negative values:
		718
		719	for (m = -100; m <= 100; ++m)
		720	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		721
		722	=item x = ecb_div_rd (val, div)
		723
		724	=item x = ecb_div_ru (val, div)
		725
		726	Returns C<val> divided by C<div> rounded down or up, respectively.
		727	C<val> and C<div> must have integer types and C<div> must be strictly
		728	positive. Note that these functions are implemented with macros in C
		729	and with function templates in C++.
319		730
320	=back	731	=back
321		732
322	=head2 UTILITY	733	=head2 UTILITY
323		734
324	=over 4	735	=over 4
325		736
326	=item element_count = ecb_array_length (name) [MACRO]	737	=item element_count = ecb_array_length (name)
327		738
328	Returns the number of elements in the array C<name>. For example:	739	Returns the number of elements in the array C<name>. For example:
329		740
330	int primes[] = { 2, 3, 5, 7, 11 };	741	int primes[] = { 2, 3, 5, 7, 11 };
331	int sum = 0;	742	int sum = 0;
…		…
333	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
334	sum += primes [i];	745	sum += primes [i];
335		746
336	=back	747	=back
337		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
338		750
		751	These symbols need to be defined before including F<ecb.h> the first time.
		752
		753	=over 4
		754
		755	=item ECB_NO_THREADS
		756
		757	If F<ecb.h> is never used from multiple threads, then this symbol can
		758	be defined, in which case memory fences (and similar constructs) are
		759	completely removed, leading to more efficient code and fewer dependencies.
		760
		761	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		762
		763	=item ECB_NO_SMP
		764
		765	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		766	multiple threads, but never concurrently (e.g. if the system the program
		767	runs on has only a single CPU with a single core, no hyperthreading and so
		768	on), then this symbol can be defined, leading to more efficient code and
		769	fewer dependencies.
		770
		771	=item ECB_NO_LIBM
		772
		773	When defined to C<1>, do not export any functions that might introduce
		774	dependencies on the math library (usually called F<-lm>) - these are
		775	marked with [-UECB_NO_LIBM].
		776
		777	=back
		778
		779

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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 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 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 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC