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Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC vs.
Revision 1.52 by root, Sun Sep 23 22:32:33 2012 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	which is typically true for both C and C++ compilers.
		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.
		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.
		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	=back
		156
55	=head2 GCC ATTRIBUTES	157	=head2 GCC ATTRIBUTES
56		158
57	blabla where to put, what others	159	A major part of libecb deals with GCC attributes. These are additional
		160	attributes that you can assign to functions, variables and sometimes even
		161	types - much like C<const> or C<volatile> in C.
		162
		163	While GCC allows declarations to show up in many surprising places,
		164	but not in many expected places, the safest way is to put attribute
		165	declarations before the whole declaration:
		166
		167	ecb_const int mysqrt (int a);
		168	ecb_unused int i;
		169
		170	For variables, it is often nicer to put the attribute after the name, and
		171	avoid multiple declarations using commas:
		172
		173	int i ecb_unused;
58		174
59	=over 4	175	=over 4
60		176
61	=item ecb_attribute ((attrs...))	177	=item ecb_attribute ((attrs...))
62		178
63	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and	179	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.	180	nothing on other compilers, so the effect is that only GCC sees these.
		181
		182	Example: use the C<deprecated> attribute on a function.
		183
		184	ecb_attribute((__deprecated__)) void
		185	do_not_use_me_anymore (void);
65		186
66	=item ecb_unused	187	=item ecb_unused
67		188
68	Marks a function or a variable as "unused", which simply suppresses a	189	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.	190	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:	191	declare a variable but do not always use it:
71		192
		193	{
		194	int var ecb_unused;
		195
		196	#ifdef SOMECONDITION
		197	var = ...;
		198	return var;
		199	#else
		200	return 0;
		201	#endif
		202	}
		203
		204	=item ecb_inline
		205
		206	This is not actually an attribute, but you use it like one. It expands
		207	either to C<static inline> or to just C<static>, if inline isn't
		208	supported. It should be used to declare functions that should be inlined,
		209	for code size or speed reasons.
		210
		211	Example: inline this function, it surely will reduce codesize.
		212
		213	ecb_inline int
		214	negmul (int a, int b)
72	{	215	{
73	int var ecb_unused;	216	return - (a * b);
74
75	#ifdef SOMECONDITION
76	var = ...;
77	return var;
78	#else
79	return 0;
80	#endif
81	}	217	}
82		218
83	=item ecb_noinline	219	=item ecb_noinline
84		220
85	Prevent a function from being inlined - it might be optimised away, but	221	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	222	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.	223	is rarely called and large enough for inlining not to be helpful.
88		224
89	=item ecb_noreturn	225	=item ecb_noreturn
90		226
		227	Marks a function as "not returning, ever". Some typical functions that
		228	don't return are C<exit> or C<abort> (which really works hard to not
		229	return), and now you can make your own:
		230
		231	ecb_noreturn void
		232	my_abort (const char *errline)
		233	{
		234	puts (errline);
		235	abort ();
		236	}
		237
		238	In this case, the compiler would probably be smart enough to deduce it on
		239	its own, so this is mainly useful for declarations.
		240
91	=item ecb_const	241	=item ecb_const
92		242
		243	Declares that the function only depends on the values of its arguments,
		244	much like a mathematical function. It specifically does not read or write
		245	any memory any arguments might point to, global variables, or call any
		246	non-const functions. It also must not have any side effects.
		247
		248	Such a function can be optimised much more aggressively by the compiler -
		249	for example, multiple calls with the same arguments can be optimised into
		250	a single call, which wouldn't be possible if the compiler would have to
		251	expect any side effects.
		252
		253	It is best suited for functions in the sense of mathematical functions,
		254	such as a function returning the square root of its input argument.
		255
		256	Not suited would be a function that calculates the hash of some memory
		257	area you pass in, prints some messages or looks at a global variable to
		258	decide on rounding.
		259
		260	See C<ecb_pure> for a slightly less restrictive class of functions.
		261
93	=item ecb_pure	262	=item ecb_pure
94		263
		264	Similar to C<ecb_const>, declares a function that has no side
		265	effects. Unlike C<ecb_const>, the function is allowed to examine global
		266	variables and any other memory areas (such as the ones passed to it via
		267	pointers).
		268
		269	While these functions cannot be optimised as aggressively as C<ecb_const>
		270	functions, they can still be optimised away in many occasions, and the
		271	compiler has more freedom in moving calls to them around.
		272
		273	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		274	function that calculates the MD5 sum of some input and updates some MD5
		275	state passed as argument would I<NOT> be pure, however, as it would modify
		276	some memory area that is not the return value.
		277
95	=item ecb_hot	278	=item ecb_hot
96		279
		280	This declares a function as "hot" with regards to the cache - the function
		281	is used so often, that it is very beneficial to keep it in the cache if
		282	possible.
		283
		284	The compiler reacts by trying to place hot functions near to each other in
		285	memory.
		286
		287	Whether a function is hot or not often depends on the whole program,
		288	and less on the function itself. C<ecb_cold> is likely more useful in
		289	practise.
		290
97	=item ecb_cold	291	=item ecb_cold
98		292
		293	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		294	the cache, or in other words, this function is not called often, or not at
		295	speed-critical times, and keeping it in the cache might be a waste of said
		296	cache.
		297
		298	In addition to placing cold functions together (or at least away from hot
		299	functions), this knowledge can be used in other ways, for example, the
		300	function will be optimised for size, as opposed to speed, and codepaths
		301	leading to calls to those functions can automatically be marked as if
		302	C<ecb_expect_false> had been used to reach them.
		303
		304	Good examples for such functions would be error reporting functions, or
		305	functions only called in exceptional or rare cases.
		306
99	=item ecb_artificial	307	=item ecb_artificial
		308
		309	Declares the function as "artificial", in this case meaning that this
		310	function is not really meant to be a function, but more like an accessor
		311	- many methods in C++ classes are mere accessor functions, and having a
		312	crash reported in such a method, or single-stepping through them, is not
		313	usually so helpful, especially when it's inlined to just a few instructions.
		314
		315	Marking them as artificial will instruct the debugger about just this,
		316	leading to happier debugging and thus happier lives.
		317
		318	Example: in some kind of smart-pointer class, mark the pointer accessor as
		319	artificial, so that the whole class acts more like a pointer and less like
		320	some C++ abstraction monster.
		321
		322	template<typename T>
		323	struct my_smart_ptr
		324	{
		325	T *value;
		326
		327	ecb_artificial
		328	operator T *()
		329	{
		330	return value;
		331	}
		332	};
100		333
101	=back	334	=back
102		335
103	=head2 OPTIMISATION HINTS	336	=head2 OPTIMISATION HINTS
104		337
…		…
136		369
137	Evaluates C<expr> and returns it. In addition, it tells the compiler that	370	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	371	the C<expr> evaluates to C<value> a lot, which can be used for static
139	branch optimisations.	372	branch optimisations.
140		373
141	Usually, you want to use the more intuitive C<ecb_likely> and	374	Usually, you want to use the more intuitive C<ecb_expect_true> and
142	C<ecb_unlikely> functions instead.	375	C<ecb_expect_false> functions instead.
143		376
144	=item bool ecb_likely (bool)	377	=item bool ecb_expect_true (cond)
145		378
146	=item bool ecb_unlikely (bool)	379	=item bool ecb_expect_false (cond)
147		380
148	These two functions expect a expression that is true or false and return	381	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	382	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:	383	other conditional statement, it will not change the program:
151		384
152	/* these two do the same thing */	385	/* these two do the same thing */
153	if (some_condition) ...;	386	if (some_condition) ...;
154	if (ecb_likely (some_condition)) ...;	387	if (ecb_expect_true (some_condition)) ...;
155		388
156	However, by using C<ecb_likely>, you tell the compiler that the condition	389	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	390	condition is likely to be true (and for C<ecb_expect_false>, that it is
158	true).	391	unlikely to be true).
159		392
160	For example, when you check for a null pointer and expect this to be a	393	For example, when you check for a null pointer and expect this to be a
161	rare, exceptional, case, then use C<ecb_unlikely>:	394	rare, exceptional, case, then use C<ecb_expect_false>:
162		395
163	void my_free (void *ptr)	396	void my_free (void *ptr)
164	{	397	{
165	if (ecb_unlikely (ptr == 0))	398	if (ecb_expect_false (ptr == 0))
166	return;	399	return;
167	}	400	}
168		401
169	Consequent use of these functions to mark away exceptional cases or to	402	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	403	tell the compiler what the hot path through a function is can increase
171	performance considerably.	404	performance considerably.
		405
		406	You might know these functions under the name C<likely> and C<unlikely>
		407	- while these are common aliases, we find that the expect name is easier
		408	to understand when quickly skimming code. If you wish, you can use
		409	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		410	C<ecb_expect_false> - these are simply aliases.
172		411
173	A very good example is in a function that reserves more space for some	412	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) -	413	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	414	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:	415	you expect that most checks will turn out to be false:
177		416
178	/* make sure we have "size" extra room in our buffer */	417	/* make sure we have "size" extra room in our buffer */
179	ecb_inline void	418	ecb_inline void
180	reserve (int size)	419	reserve (int size)
181	{	420	{
182	if (ecb_unlikely (current + size > end))	421	if (ecb_expect_false (current + size > end))
183	real_reserve_method (size); /* presumably noinline */	422	real_reserve_method (size); /* presumably noinline */
184	}	423	}
185		424
186	=item bool ecb_assume (cond)	425	=item bool ecb_assume (cond)
187		426
…		…
190		429
191	This can be used to teach the compiler about invariants or other	430	This can be used to teach the compiler about invariants or other
192	conditions that might improve code generation, but which are impossible to	431	conditions that might improve code generation, but which are impossible to
193	deduce form the code itself.	432	deduce form the code itself.
194		433
195	For example, the example reservation function from the C<ecb_unlikely>	434	For example, the example reservation function from the C<ecb_expect_false>
196	description could be written thus (only C<ecb_assume> was added):	435	description could be written thus (only C<ecb_assume> was added):
197		436
198	ecb_inline void	437	ecb_inline void
199	reserve (int size)	438	reserve (int size)
200	{	439	{
201	if (ecb_unlikely (current + size > end))	440	if (ecb_expect_false (current + size > end))
202	real_reserve_method (size); /* presumably noinline */	441	real_reserve_method (size); /* presumably noinline */
203		442
204	ecb_assume (current + size <= end);	443	ecb_assume (current + size <= end);
205	}	444	}
206		445
…		…
255	After processing the node, (part of) the next node might already be in	494	After processing the node, (part of) the next node might already be in
256	cache.	495	cache.
257		496
258	=back	497	=back
259		498
260	=head2 BIT FIDDLING / BITSTUFFS	499	=head2 BIT FIDDLING / BIT WIZARDRY
261		500
262	=over 4	501	=over 4
263		502
264	=item bool ecb_big_endian ()	503	=item bool ecb_big_endian ()
265		504
…		…
267		506
268	These two functions return true if the byte order is big endian	507	These two functions return true if the byte order is big endian
269	(most-significant byte first) or little endian (least-significant byte	508	(most-significant byte first) or little endian (least-significant byte
270	first) respectively.	509	first) respectively.
271		510
		511	On systems that are neither, their return values are unspecified.
		512
272	=item int ecb_ctz32 (uint32_t x)	513	=item int ecb_ctz32 (uint32_t x)
273		514
		515	=item int ecb_ctz64 (uint64_t x)
		516
274	Returns the index of the least significant bit set in C<x> (or	517	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	518	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	519	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		520
		521	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		522
		523	For example:
		524
280	ecb_ctz32(3) = 0	525	ecb_ctz32 (3) = 0
281	ecb_ctz32(6) = 1	526	ecb_ctz32 (6) = 1
		527
		528	=item bool ecb_is_pot32 (uint32_t x)
		529
		530	=item bool ecb_is_pot64 (uint32_t x)
		531
		532	Return true iff C<x> is a power of two or C<x == 0>.
		533
		534	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		535
		536	=item int ecb_ld32 (uint32_t x)
		537
		538	=item int ecb_ld64 (uint64_t x)
		539
		540	Returns the index of the most significant bit set in C<x>, or the number
		541	of digits the number requires in binary (so that C<< 2**ld <= x <
		542	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		543	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		544	example to see how many bits a certain number requires to be encoded.
		545
		546	This function is similar to the "count leading zero bits" function, except
		547	that that one returns how many zero bits are "in front" of the number (in
		548	the given data type), while C<ecb_ld> returns how many bits the number
		549	itself requires.
		550
		551	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
282		552
283	=item int ecb_popcount32 (uint32_t x)	553	=item int ecb_popcount32 (uint32_t x)
284		554
		555	=item int ecb_popcount64 (uint64_t x)
		556
285	Returns the number of bits set to 1 in C<x>. For example:	557	Returns the number of bits set to 1 in C<x>.
286		558
		559	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		560
		561	For example:
		562
287	ecb_popcount32(7) = 3	563	ecb_popcount32 (7) = 3
288	ecb_popcount32(255) = 8	564	ecb_popcount32 (255) = 8
		565
		566	=item uint8_t ecb_bitrev8 (uint8_t x)
		567
		568	=item uint16_t ecb_bitrev16 (uint16_t x)
		569
		570	=item uint32_t ecb_bitrev32 (uint32_t x)
		571
		572	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		573	and so on.
		574
		575	Example:
		576
		577	ecb_bitrev8 (0xa7) = 0xea
		578	ecb_bitrev32 (0xffcc4411) = 0x882233ff
289		579
290	=item uint32_t ecb_bswap16 (uint32_t x)	580	=item uint32_t ecb_bswap16 (uint32_t x)
291		581
292	=item uint32_t ecb_bswap32 (uint32_t x)	582	=item uint32_t ecb_bswap32 (uint32_t x)
293		583
		584	=item uint64_t ecb_bswap64 (uint64_t x)
		585
294	These two functions return the value of the 16-bit (32-bit) variable	586	These functions return the value of the 16-bit (32-bit, 64-bit) value
295	C<x> after reversing the order of bytes.	587	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		588	C<ecb_bswap32>).
		589
		590	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		591
		592	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		593
		594	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		595
		596	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		597
		598	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		599
		600	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
296		601
297	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	602	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
298		603
299	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	604	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
300		605
301	These two functions return the value of C<x> after shifting all the bits	606	These two families of functions return the value of C<x> after rotating
302	by C<count> positions to the right or left respectively.	607	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		608	(C<ecb_rotl>).
		609
		610	Current GCC versions understand these functions and usually compile them
		611	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		612	x86).
303		613
304	=back	614	=back
305		615
		616	=head2 FLOATING POINT FIDDLING
		617
		618	=over 4
		619
		620	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		621
		622	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		623
		624	These functions each take an argument in the native C<float> or C<double>
		625	type and return the IEEE 754 bit representation of it.
		626
		627	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		628	will be the most significant bit, followed by exponent and mantissa.
		629
		630	This function should work even when the native floating point format isn't
		631	IEEE compliant, of course at a speed and code size penalty, and of course
		632	also within reasonable limits (it tries to convert NaNs, infinities and
		633	denormals, but will likely convert negative zero to positive zero).
		634
		635	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		636	be able to optimise away this function completely.
		637
		638	These functions can be helpful when serialising floats to the network - you
		639	can serialise the return value like a normal uint32_t/uint64_t.
		640
		641	Another use for these functions is to manipulate floating point values
		642	directly.
		643
		644	Silly example: toggle the sign bit of a float.
		645
		646	/* On gcc-4.7 on amd64, */
		647	/* this results in a single add instruction to toggle the bit, and 4 extra */
		648	/* instructions to move the float value to an integer register and back. */
		649
		650	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		651
		652	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		653
		654	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		655
		656	The reverse operation of the previos function - takes the bit representation
		657	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		658	or C<double> format.
		659
		660	This function should work even when the native floating point format isn't
		661	IEEE compliant, of course at a speed and code size penalty, and of course
		662	also within reasonable limits (it tries to convert normals and denormals,
		663	and might be lucky for infinities, and with extraordinary luck, also for
		664	negative zero).
		665
		666	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		667	be able to optimise away this function completely.
		668
		669	=back
		670
306	=head2 ARITHMETIC	671	=head2 ARITHMETIC
307		672
308	=over 4	673	=over 4
309		674
310	=item x = ecb_mod (m, n)	675	=item x = ecb_mod (m, n)
311		676
312	Returns the positive remainder of the modulo operation between C<m> and	677	Returns C<m> modulo C<n>, which is the same as the positive remainder
		678	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	679	division. Unlike the C remainder operator C<%>, this function ensures that
314	return value is always positive).	680	the return value is always positive and that the two numbers I<m> and
		681	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		682	C<ecb_mod> implements the mathematical modulo operation, which is missing
		683	in the language.
315		684
316	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	685	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	686	negatable, that is, both C<m> and C<-m> must be representable in its
318	type.	687	type (this typically excludes the minimum signed integer value, the same
		688	limitation as for C</> and C<%> in C).
		689
		690	Current GCC versions compile this into an efficient branchless sequence on
		691	almost all CPUs.
		692
		693	For example, when you want to rotate forward through the members of an
		694	array for increasing C<m> (which might be negative), then you should use
		695	C<ecb_mod>, as the C<%> operator might give either negative results, or
		696	change direction for negative values:
		697
		698	for (m = -100; m <= 100; ++m)
		699	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		700
		701	=item x = ecb_div_rd (val, div)
		702
		703	=item x = ecb_div_ru (val, div)
		704
		705	Returns C<val> divided by C<div> rounded down or up, respectively.
		706	C<val> and C<div> must have integer types and C<div> must be strictly
		707	positive. Note that these functions are implemented with macros in C
		708	and with function templates in C++.
319		709
320	=back	710	=back
321		711
322	=head2 UTILITY	712	=head2 UTILITY
323		713
324	=over 4	714	=over 4
325		715
326	=item element_count = ecb_array_length (name) [MACRO]	716	=item element_count = ecb_array_length (name)
327		717
328	Returns the number of elements in the array C<name>. For example:	718	Returns the number of elements in the array C<name>. For example:
329		719
330	int primes[] = { 2, 3, 5, 7, 11 };	720	int primes[] = { 2, 3, 5, 7, 11 };
331	int sum = 0;	721	int sum = 0;
…		…
333	for (i = 0; i < ecb_array_length (primes); i++)	723	for (i = 0; i < ecb_array_length (primes); i++)
334	sum += primes [i];	724	sum += primes [i];
335		725
336	=back	726	=back
337		727
		728	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
338		729
		730	These symbols need to be defined before including F<ecb.h> the first time.
		731
		732	=over 4
		733
		734	=item ECB_NO_THREADS
		735
		736	If F<ecb.h> is never used from multiple threads, then this symbol can
		737	be defined, in which case memory fences (and similar constructs) are
		738	completely removed, leading to more efficient code and fewer dependencies.
		739
		740	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		741
		742	=item ECB_NO_SMP
		743
		744	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		745	multiple threads, but never concurrently (e.g. if the system the program
		746	runs on has only a single CPU with a single core, no hyperthreading and so
		747	on), then this symbol can be defined, leading to more efficient code and
		748	fewer dependencies.
		749
		750	=item ECB_NO_LIBM
		751
		752	When defined to C<1>, do not export any functions that might introduce
		753	dependencies on the math library (usually called F<-lm>) - these are
		754	marked with [-UECB_NO_LIBM].
		755
		756	=back
		757
		758

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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 1.52 by root, Sun Sep 23 22:32:33 2012 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 1.52 by root, Sun Sep 23 22:32:33 2012 UTC