[ViewVC] Diff of: cvs/libecb/ecb.pod

Comparing libecb/ecb.pod (file contents):
Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.101 by root, Mon Nov 22 17:15:50 2021 UTC

…		…
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 many compiler built-ins,
16	with replacement functions for other compilers. In addition to this,	16	together with replacement functions for other compilers. In addition
17	it provides a number of other lowlevel C utilities, such as endianness	17	to this, it provides a number of other lowlevel C utilities, such as
18	detection, byte swapping or bit rotations.	18	endianness detection, byte swapping or bit rotations.
19		19
20	Or in other words, things that should be built-in into any standard C	20	Or in other words, things that should be built into any standard C
21	system, but aren't.	21	system, but aren't, implemented as efficient as possible with GCC (clang,
		22	msvc...), and still correct with other compilers.
22		23
23	More might come.	24	More might come.
24		25
25	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
26		27
…		…
53	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
54	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
55	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
56	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
57		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_
		64	int16_t uint16_t
		65	int32_t uint32_
		66	int64_t uint64_t
		67	int_fast8_t uint_fast8_t
		68	int_fast16_t uint_fast16_t
		69	int_fast32_t uint_fast32_t
		70	int_fast64_t uint_fast64_t
		71	intptr_t uintptr_t
		72
		73	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
		74	platform (currently C<4> or C<8>) and can be used in preprocessor
		75	expressions.
		76
		77	For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>.
		78
		79	=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
		80
		81	All the following symbols expand to an expression that can be tested in
		82	preprocessor instructions as well as treated as a boolean (use C<!!> to
		83	ensure it's either C<0> or C<1> if you need that).
		84
		85	=over
		86
		87	=item ECB_C
		88
		89	True if the implementation defines the C<__STDC__> macro to a true value,
		90	while not claiming to be C++, i..e C, but not C++.
		91
		92	=item ECB_C99
		93
		94	True if the implementation claims to be compliant to C99 (ISO/IEC
		95	9899:1999) or any later version, while not claiming to be C++.
		96
		97	Note that later versions (ECB_C11) remove core features again (for
		98	example, variable length arrays).
		99
		100	=item ECB_C11, ECB_C17
		101
		102	True if the implementation claims to be compliant to C11/C17 (ISO/IEC
		103	9899:2011, :20187) or any later version, while not claiming to be C++.
		104
		105	=item ECB_CPP
		106
		107	True if the implementation defines the C<__cplusplus__> macro to a true
		108	value, which is typically true for C++ compilers.
		109
		110	=item ECB_CPP11, ECB_CPP14, ECB_CPP17
		111
		112	True if the implementation claims to be compliant to C++11/C++14/C++17
		113	(ISO/IEC 14882:2011, :2014, :2017) or any later version.
		114
		115	Note that many C++20 features will likely have their own feature test
		116	macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>).
		117
		118	=item ECB_OPTIMIZE_SIZE
		119
		120	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
		121	can also be defined before including F<ecb.h>, in which case it will be
		122	unchanged.
		123
		124	=item ECB_GCC_VERSION (major, minor)
		125
		126	Expands to a true value (suitable for testing by the preprocessor) if the
		127	compiler used is GNU C and the version is the given version, or higher.
		128
		129	This macro tries to return false on compilers that claim to be GCC
		130	compatible but aren't.
		131
		132	=item ECB_EXTERN_C
		133
		134	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		135
		136	This can be used to declare a single external C function:
		137
		138	ECB_EXTERN_C int printf (const char *format, ...);
		139
		140	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		141
		142	These two macros can be used to wrap multiple C<extern "C"> definitions -
		143	they expand to nothing in C.
		144
		145	They are most useful in header files:
		146
		147	ECB_EXTERN_C_BEG
		148
		149	int mycfun1 (int x);
		150	int mycfun2 (int x);
		151
		152	ECB_EXTERN_C_END
		153
		154	=item ECB_STDFP
		155
		156	If this evaluates to a true value (suitable for testing by the
		157	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		158	and double/binary64 representations internally I<and> the endianness of
		159	both types match the endianness of C<uint32_t> and C<uint64_t>.
		160
		161	This means you can just copy the bits of a C<float> (or C<double>) to an
		162	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		163	without having to think about format or endianness.
		164
		165	This is true for basically all modern platforms, although F<ecb.h> might
		166	not be able to deduce this correctly everywhere and might err on the safe
		167	side.
		168
		169	=item ECB_64BIT_NATIVE
		170
		171	Evaluates to a true value (suitable for both preprocessor and C code
		172	testing) if 64 bit integer types on this architecture are evaluated
		173	"natively", that is, with similar speeds as 32 bit integers. While 64 bit
		174	integer support is very common (and in fact required by libecb), 32 bit
		175	cpus have to emulate operations on them, so you might want to avoid them.
		176
		177	=item ECB_AMD64, ECB_AMD64_X32
		178
		179	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		180	ABI, respectively, and undefined elsewhere.
		181
		182	The designers of the new X32 ABI for some inexplicable reason decided to
		183	make it look exactly like amd64, even though it's completely incompatible
		184	to that ABI, breaking about every piece of software that assumed that
		185	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		186	necessary.
		187
		188	=back
		189
		190	=head2 MACRO TRICKERY
		191
		192	=over
		193
		194	=item ECB_CONCAT (a, b)
		195
		196	Expands any macros in C<a> and C<b>, then concatenates the result to form
		197	a single token. This is mainly useful to form identifiers from components,
		198	e.g.:
		199
		200	#define S1 str
		201	#define S2 cpy
		202
		203	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		204
		205	=item ECB_STRINGIFY (arg)
		206
		207	Expands any macros in C<arg> and returns the stringified version of
		208	it. This is mainly useful to get the contents of a macro in string form,
		209	e.g.:
		210
		211	#define SQL_LIMIT 100
		212	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		213
		214	=item ECB_STRINGIFY_EXPR (expr)
		215
		216	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		217	is a valid expression. This is useful to catch typos or cases where the
		218	macro isn't available:
		219
		220	#include <errno.h>
		221
		222	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		223	ECB_STRINGIFY_EXPR (EDOM); // "33"
		224
		225	// now imagine we had a typo:
		226
		227	ECB_STRINGIFY (EDAM); // "EDAM"
		228	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		229
		230	=back
		231
58	=head2 GCC ATTRIBUTES	232	=head2 ATTRIBUTES
59		233
60	blabla where to put, what others	234	A major part of libecb deals with additional attributes that can be
		235	assigned to functions, variables and sometimes even types - much like
		236	C<const> or C<volatile> in C. They are implemented using either GCC
		237	attributes or other compiler/language specific features. Attributes
		238	declarations must be put before the whole declaration:
61		239
		240	ecb_const int mysqrt (int a);
		241	ecb_unused int i;
		242
62	=over 4	243	=over
63
64	=item ecb_attribute ((attrs...))
65
66	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
67	nothing on other compilers, so the effect is that only GCC sees these.
68
69	Example: use the C<deprecated> attribute on a function.
70
71	ecb_attribute((__deprecated__)) void
72	do_not_use_me_anymore (void);
73		244
74	=item ecb_unused	245	=item ecb_unused
75		246
76	Marks a function or a variable as "unused", which simply suppresses a	247	Marks a function or a variable as "unused", which simply suppresses a
77	warning by GCC when it detects it as unused. This is useful when you e.g.	248	warning by the compiler when it detects it as unused. This is useful when
78	declare a variable but do not always use it:	249	you e.g. declare a variable but do not always use it:
79		250
80	{	251	{
81	int var ecb_unused;	252	ecb_unused int var;
82		253
83	#ifdef SOMECONDITION	254	#ifdef SOMECONDITION
84	var = ...;	255	var = ...;
85	return var;	256	return var;
86	#else	257	#else
87	return 0;	258	return 0;
88	#endif	259	#endif
89	}	260	}
90		261
		262	=item ecb_deprecated
		263
		264	Similar to C<ecb_unused>, but marks a function, variable or type as
		265	deprecated. This makes some compilers warn when the type is used.
		266
		267	=item ecb_deprecated_message (message)
		268
		269	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		270	used instead of a generic depreciation message when the object is being
		271	used.
		272
		273	=item ecb_inline
		274
		275	Expands either to (a compiler-specific equivalent of) C<static inline> or
		276	to just C<static>, if inline isn't supported. It should be used to declare
		277	functions that should be inlined, for code size or speed reasons.
		278
		279	Example: inline this function, it surely will reduce codesize.
		280
		281	ecb_inline int
		282	negmul (int a, int b)
		283	{
		284	return - (a * b);
		285	}
		286
91	=item ecb_noinline	287	=item ecb_noinline
92		288
93	Prevent a function from being inlined - it might be optimised away, but	289	Prevents a function from being inlined - it might be optimised away, but
94	not inlined into other functions. This is useful if you know your function	290	not inlined into other functions. This is useful if you know your function
95	is rarely called and large enough for inlining not to be helpful.	291	is rarely called and large enough for inlining not to be helpful.
96		292
97	=item ecb_noreturn	293	=item ecb_noreturn
98		294
…		…
105	{	301	{
106	puts (errline);	302	puts (errline);
107	abort ();	303	abort ();
108	}	304	}
109		305
110	In this case, the compiler would probbaly be smart enough to decude it on	306	In this case, the compiler would probably be smart enough to deduce it on
111	it's own, so this is mainly useful for declarations.	307	its own, so this is mainly useful for declarations.
		308
		309	=item ecb_restrict
		310
		311	Expands to the C<restrict> keyword or equivalent on compilers that support
		312	them, and to nothing on others. Must be specified on a pointer type or
		313	an array index to indicate that the memory doesn't alias with any other
		314	restricted pointer in the same scope.
		315
		316	Example: multiply a vector, and allow the compiler to parallelise the
		317	loop, because it knows it doesn't overwrite input values.
		318
		319	void
		320	multiply (ecb_restrict float *src,
		321	ecb_restrict float *dst,
		322	int len, float factor)
		323	{
		324	int i;
		325
		326	for (i = 0; i < len; ++i)
		327	dst [i] = src [i] * factor;
		328	}
112		329
113	=item ecb_const	330	=item ecb_const
114		331
115	Declares that the function only depends on the values of it's arguments,	332	Declares that the function only depends on the values of its arguments,
116	much like a mathematical function. It specifically does not read or write	333	much like a mathematical function. It specifically does not read or write
117	any memory any arguments might point to, global variables, or call any	334	any memory any arguments might point to, global variables, or call any
118	non-const functions. It also must not have any side effects.	335	non-const functions. It also must not have any side effects.
119		336
120	Such a function can be optimised much more aggressively by the compiler -	337	Such a function can be optimised much more aggressively by the compiler -
121	for example, multiple calls with the same arguments can be optimised into	338	for example, multiple calls with the same arguments can be optimised into
122	a single call, which wouldn't be possible if the compiler would have to	339	a single call, which wouldn't be possible if the compiler would have to
123	expect any side effects.	340	expect any side effects.
124		341
125	It is best suited for functions in the sense of mathematical functions,	342	It is best suited for functions in the sense of mathematical functions,
126	such as a function return the square root of its input argument.	343	such as a function returning the square root of its input argument.
127		344
128	Not suited would be a function that calculates the hash of some memory	345	Not suited would be a function that calculates the hash of some memory
129	area you pass in, prints some messages or looks at a global variable to	346	area you pass in, prints some messages or looks at a global variable to
130	decide on rounding.	347	decide on rounding.
131		348
…		…
154	possible.	371	possible.
155		372
156	The compiler reacts by trying to place hot functions near to each other in	373	The compiler reacts by trying to place hot functions near to each other in
157	memory.	374	memory.
158		375
159	Whether a function is hot or not often depend son the whole program,	376	Whether a function is hot or not often depends on the whole program,
160	and less on the function itself. C<ecb_cold> is likely more useful in	377	and less on the function itself. C<ecb_cold> is likely more useful in
161	practise.	378	practise.
162		379
163	=item ecb_cold	380	=item ecb_cold
164		381
…		…
169		386
170	In addition to placing cold functions together (or at least away from hot	387	In addition to placing cold functions together (or at least away from hot
171	functions), this knowledge can be used in other ways, for example, the	388	functions), this knowledge can be used in other ways, for example, the
172	function will be optimised for size, as opposed to speed, and codepaths	389	function will be optimised for size, as opposed to speed, and codepaths
173	leading to calls to those functions can automatically be marked as if	390	leading to calls to those functions can automatically be marked as if
174	C<ecb_unlikel> had been used to reach them.	391	C<ecb_expect_false> had been used to reach them.
175		392
176	Good examples for such functions would be error reporting functions, or	393	Good examples for such functions would be error reporting functions, or
177	functions only called in exceptional or rare cases.	394	functions only called in exceptional or rare cases.
178		395
179	=item ecb_artificial	396	=item ecb_artificial
180		397
181	Declares the function as "artificial", in this case meaning that this	398	Declares the function as "artificial", in this case meaning that this
182	function is not really mean to be a function, but more like an accessor	399	function is not really meant to be a function, but more like an accessor
183	- many methods in C++ classes are mere accessor functions, and having a	400	- many methods in C++ classes are mere accessor functions, and having a
184	crash reported in such a method, or single-stepping through them, is not	401	crash reported in such a method, or single-stepping through them, is not
185	usually so helpful, especially when it's inlined to just a few instructions.	402	usually so helpful, especially when it's inlined to just a few instructions.
186		403
187	Marking them as artificial will instruct the debugger about just this,	404	Marking them as artificial will instruct the debugger about just this,
…		…
205		422
206	=back	423	=back
207		424
208	=head2 OPTIMISATION HINTS	425	=head2 OPTIMISATION HINTS
209		426
210	=over 4	427	=over
211		428
212	=item bool ecb_is_constant(expr)	429	=item bool ecb_is_constant (expr)
213		430
214	Returns true iff the expression can be deduced to be a compile-time	431	Returns true iff the expression can be deduced to be a compile-time
215	constant, and false otherwise.	432	constant, and false otherwise.
216		433
217	For example, when you have a C<rndm16> function that returns a 16 bit	434	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
235	return is_constant (n) && !(n & (n - 1))	452	return is_constant (n) && !(n & (n - 1))
236	? rndm16 () & (num - 1)	453	? rndm16 () & (num - 1)
237	: (n * (uint32_t)rndm16 ()) >> 16;	454	: (n * (uint32_t)rndm16 ()) >> 16;
238	}	455	}
239		456
240	=item bool ecb_expect (expr, value)	457	=item ecb_expect (expr, value)
241		458
242	Evaluates C<expr> and returns it. In addition, it tells the compiler that	459	Evaluates C<expr> and returns it. In addition, it tells the compiler that
243	the C<expr> evaluates to C<value> a lot, which can be used for static	460	the C<expr> evaluates to C<value> a lot, which can be used for static
244	branch optimisations.	461	branch optimisations.
245		462
246	Usually, you want to use the more intuitive C<ecb_likely> and	463	Usually, you want to use the more intuitive C<ecb_expect_true> and
247	C<ecb_unlikely> functions instead.	464	C<ecb_expect_false> functions instead.
248		465
		466	=item bool ecb_expect_true (cond)
		467
249	=item bool ecb_likely (cond)	468	=item bool ecb_expect_false (cond)
250
251	=item bool ecb_unlikely (cond)
252		469
253	These two functions expect a expression that is true or false and return	470	These two functions expect a expression that is true or false and return
254	C<1> or C<0>, respectively, so when used in the condition of an C<if> or	471	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
255	other conditional statement, it will not change the program:	472	other conditional statement, it will not change the program:
256		473
257	/* these two do the same thing */	474	/* these two do the same thing */
258	if (some_condition) ...;	475	if (some_condition) ...;
259	if (ecb_likely (some_condition)) ...;	476	if (ecb_expect_true (some_condition)) ...;
260		477
261	However, by using C<ecb_likely>, you tell the compiler that the condition	478	However, by using C<ecb_expect_true>, you tell the compiler that the
262	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be	479	condition is likely to be true (and for C<ecb_expect_false>, that it is
263	true).	480	unlikely to be true).
264		481
265	For example, when you check for a null pointer and expect this to be a	482	For example, when you check for a null pointer and expect this to be a
266	rare, exceptional, case, then use C<ecb_unlikely>:	483	rare, exceptional, case, then use C<ecb_expect_false>:
267		484
268	void my_free (void *ptr)	485	void my_free (void *ptr)
269	{	486	{
270	if (ecb_unlikely (ptr == 0))	487	if (ecb_expect_false (ptr == 0))
271	return;	488	return;
272	}	489	}
273		490
274	Consequent use of these functions to mark away exceptional cases or to	491	Consequent use of these functions to mark away exceptional cases or to
275	tell the compiler what the hot path through a function is can increase	492	tell the compiler what the hot path through a function is can increase
276	performance considerably.	493	performance considerably.
		494
		495	You might know these functions under the name C<likely> and C<unlikely>
		496	- while these are common aliases, we find that the expect name is easier
		497	to understand when quickly skimming code. If you wish, you can use
		498	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		499	C<ecb_expect_false> - these are simply aliases.
277		500
278	A very good example is in a function that reserves more space for some	501	A very good example is in a function that reserves more space for some
279	memory block (for example, inside an implementation of a string stream) -	502	memory block (for example, inside an implementation of a string stream) -
280	each time something is added, you have to check for a buffer overrun, but	503	each time something is added, you have to check for a buffer overrun, but
281	you expect that most checks will turn out to be false:	504	you expect that most checks will turn out to be false:
282		505
283	/* make sure we have "size" extra room in our buffer */	506	/* make sure we have "size" extra room in our buffer */
284	ecb_inline void	507	ecb_inline void
285	reserve (int size)	508	reserve (int size)
286	{	509	{
287	if (ecb_unlikely (current + size > end))	510	if (ecb_expect_false (current + size > end))
288	real_reserve_method (size); /* presumably noinline */	511	real_reserve_method (size); /* presumably noinline */
289	}	512	}
290		513
291	=item bool ecb_assume (cond)	514	=item ecb_assume (cond)
292		515
293	Try to tell the compiler that some condition is true, even if it's not	516	Tries to tell the compiler that some condition is true, even if it's not
294	obvious.	517	obvious. This is not a function, but a statement: it cannot be used in
		518	another expression.
295		519
296	This can be used to teach the compiler about invariants or other	520	This can be used to teach the compiler about invariants or other
297	conditions that might improve code generation, but which are impossible to	521	conditions that might improve code generation, but which are impossible to
298	deduce form the code itself.	522	deduce form the code itself.
299		523
300	For example, the example reservation function from the C<ecb_unlikely>	524	For example, the example reservation function from the C<ecb_expect_false>
301	description could be written thus (only C<ecb_assume> was added):	525	description could be written thus (only C<ecb_assume> was added):
302		526
303	ecb_inline void	527	ecb_inline void
304	reserve (int size)	528	reserve (int size)
305	{	529	{
306	if (ecb_unlikely (current + size > end))	530	if (ecb_expect_false (current + size > end))
307	real_reserve_method (size); /* presumably noinline */	531	real_reserve_method (size); /* presumably noinline */
308		532
309	ecb_assume (current + size <= end);	533	ecb_assume (current + size <= end);
310	}	534	}
311		535
…		…
316		540
317	Then the compiler I<might> be able to optimise out the second call	541	Then the compiler I<might> be able to optimise out the second call
318	completely, as it knows that C<< current + 1 > end >> is false and the	542	completely, as it knows that C<< current + 1 > end >> is false and the
319	call will never be executed.	543	call will never be executed.
320		544
321	=item bool ecb_unreachable ()	545	=item ecb_unreachable ()
322		546
323	This function does nothing itself, except tell the compiler that it will	547	This function does nothing itself, except tell the compiler that it will
324	never be executed. Apart from suppressing a warning in some cases, this	548	never be executed. Apart from suppressing a warning in some cases, this
325	function can be used to implement C<ecb_assume> or similar functions.	549	function can be used to implement C<ecb_assume> or similar functionality.
326		550
327	=item bool ecb_prefetch (addr, rw, locality)	551	=item ecb_prefetch (addr, rw, locality)
328		552
329	Tells the compiler to try to prefetch memory at the given C<addr>ess	553	Tells the compiler to try to prefetch memory at the given C<addr>ess
330	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of	554	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
331	C<0> means that there will only be one access later, C<3> means that	555	C<0> means that there will only be one access later, C<3> means that
332	the data will likely be accessed very often, and values in between mean	556	the data will likely be accessed very often, and values in between mean
333	something... in between. The memory pointed to by the address does not	557	something... in between. The memory pointed to by the address does not
334	need to be accessible (it could be a null pointer for example), but C<rw>	558	need to be accessible (it could be a null pointer for example), but C<rw>
335	and C<locality> must be compile-time constants.	559	and C<locality> must be compile-time constants.
336		560
		561	This is a statement, not a function: you cannot use it as part of an
		562	expression.
		563
337	An obvious way to use this is to prefetch some data far away, in a big	564	An obvious way to use this is to prefetch some data far away, in a big
338	array you loop over. This prefetches memory some 128 array elements later,	565	array you loop over. This prefetches memory some 128 array elements later,
339	in the hope that it will be ready when the CPU arrives at that location.	566	in the hope that it will be ready when the CPU arrives at that location.
340		567
341	int sum = 0;	568	int sum = 0;
…		…
360	After processing the node, (part of) the next node might already be in	587	After processing the node, (part of) the next node might already be in
361	cache.	588	cache.
362		589
363	=back	590	=back
364		591
365	=head2 BIT FIDDLING / BITSTUFFS	592	=head2 BIT FIDDLING / BIT WIZARDRY
366		593
367	=over 4	594	=over
368		595
369	=item bool ecb_big_endian ()	596	=item bool ecb_big_endian ()
370		597
371	=item bool ecb_little_endian ()	598	=item bool ecb_little_endian ()
372		599
373	These two functions return true if the byte order is big endian	600	These two functions return true if the byte order is big endian
374	(most-significant byte first) or little endian (least-significant byte	601	(most-significant byte first) or little endian (least-significant byte
375	first) respectively.	602	first) respectively.
376		603
		604	On systems that are neither, their return values are unspecified.
		605
377	=item int ecb_ctz32 (uint32_t x)	606	=item int ecb_ctz32 (uint32_t x)
378		607
		608	=item int ecb_ctz64 (uint64_t x)
		609
		610	=item int ecb_ctz (T x) [C++]
		611
379	Returns the index of the least significant bit set in C<x> (or	612	Returns the index of the least significant bit set in C<x> (or
380	equivalently the number of bits set to 0 before the least significant	613	equivalently the number of bits set to 0 before the least significant bit
381	bit set), starting from 0. If C<x> is 0 the result is undefined. A	614	set), starting from 0. If C<x> is 0 the result is undefined.
382	common use case is to compute the integer binary logarithm, i.e.,	615
383	floor(log2(n)). For example:	616	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		617
		618	The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
		619	C<uint32_t> and C<uint64_t> types.
		620
		621	For example:
384		622
385	ecb_ctz32 (3) = 0	623	ecb_ctz32 (3) = 0
386	ecb_ctz32 (6) = 1	624	ecb_ctz32 (6) = 1
387		625
		626	=item bool ecb_is_pot32 (uint32_t x)
		627
		628	=item bool ecb_is_pot64 (uint32_t x)
		629
		630	=item bool ecb_is_pot (T x) [C++]
		631
		632	Returns true iff C<x> is a power of two or C<x == 0>.
		633
		634	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		635
		636	The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
		637	C<uint32_t> and C<uint64_t> types.
		638
		639	=item int ecb_ld32 (uint32_t x)
		640
		641	=item int ecb_ld64 (uint64_t x)
		642
		643	=item int ecb_ld64 (T x) [C++]
		644
		645	Returns the index of the most significant bit set in C<x>, or the number
		646	of digits the number requires in binary (so that C<< 2**ld <= x <
		647	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		648	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		649	example to see how many bits a certain number requires to be encoded.
		650
		651	This function is similar to the "count leading zero bits" function, except
		652	that that one returns how many zero bits are "in front" of the number (in
		653	the given data type), while C<ecb_ld> returns how many bits the number
		654	itself requires.
		655
		656	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		657
		658	The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
		659	C<uint32_t> and C<uint64_t> types.
		660
388	=item int ecb_popcount32 (uint32_t x)	661	=item int ecb_popcount32 (uint32_t x)
389		662
		663	=item int ecb_popcount64 (uint64_t x)
		664
		665	=item int ecb_popcount (T x) [C++]
		666
390	Returns the number of bits set to 1 in C<x>. For example:	667	Returns the number of bits set to 1 in C<x>.
		668
		669	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		670
		671	The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
		672	C<uint32_t> and C<uint64_t> types.
		673
		674	For example:
391		675
392	ecb_popcount32 (7) = 3	676	ecb_popcount32 (7) = 3
393	ecb_popcount32 (255) = 8	677	ecb_popcount32 (255) = 8
394		678
		679	=item uint8_t ecb_bitrev8 (uint8_t x)
		680
		681	=item uint16_t ecb_bitrev16 (uint16_t x)
		682
		683	=item uint32_t ecb_bitrev32 (uint32_t x)
		684
		685	=item T ecb_bitrev (T x) [C++]
		686
		687	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		688	and so on.
		689
		690	The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
		691
		692	Example:
		693
		694	ecb_bitrev8 (0xa7) = 0xea
		695	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		696
		697	=item T ecb_bitrev (T x) [C++]
		698
		699	Overloaded C++ bitrev function.
		700
		701	C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
		702
395	=item uint32_t ecb_bswap16 (uint32_t x)	703	=item uint32_t ecb_bswap16 (uint32_t x)
396		704
397	=item uint32_t ecb_bswap32 (uint32_t x)	705	=item uint32_t ecb_bswap32 (uint32_t x)
398		706
		707	=item uint64_t ecb_bswap64 (uint64_t x)
		708
		709	=item T ecb_bswap (T x)
		710
399	These two functions return the value of the 16-bit (32-bit) variable	711	These functions return the value of the 16-bit (32-bit, 64-bit) value
400	C<x> after reversing the order of bytes.	712	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		713	C<ecb_bswap32>).
		714
		715	The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
		716	C<uint32_t> and C<uint64_t> types.
		717
		718	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		719
		720	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		721
		722	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		723
		724	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		725
		726	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		727
		728	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
401		729
402	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	730	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
403		731
404	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	732	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
405		733
406	These two functions return the value of C<x> after shifting all the bits	734	These two families of functions return the value of C<x> after rotating
407	by C<count> positions to the right or left respectively.	735	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		736	(C<ecb_rotl>). There are no restrictions on the value C<count>, i.e. both
		737	zero and values equal or larger than the word width work correctly. Also,
		738	notwithstanding C<count> being unsigned, negative numbers work and shift
		739	to the opposite direction.
		740
		741	Current GCC/clang versions understand these functions and usually compile
		742	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
		743	on x86).
		744
		745	=item T ecb_rotl (T x, unsigned int count) [C++]
		746
		747	=item T ecb_rotr (T x, unsigned int count) [C++]
		748
		749	Overloaded C++ rotl/rotr functions.
		750
		751	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		752
		753	=back
		754
		755	=head2 BIT MIXING, HASHING
		756
		757	Sometimes you have an integer and want to distribute its bits well, for
		758	example, to use it as a hash in a hashtable. A common example is pointer
		759	values, which often only have a limited range (e.g. low and high bits are
		760	often zero).
		761
		762	The following functions try to mix the bits to get a good bias-free
		763	distribution. They were mainly made for pointers, but the underlying
		764	integer functions are exposed as well.
		765
		766	As an added benefit, the functions are reversible, so if you find it
		767	convenient to store only the hash value, you can recover the original
		768	pointer from the hash ("unmix"), as long as your pinters are 32 or 64 bit
		769	(if this isn't the case on your platform, drop us a note and we will add
		770	functions for other bit widths).
		771
		772	The unmix functions are very slightly slower than the mix functions, so
		773	it is equally very slightly preferable to store the original values wehen
		774	convenient.
		775
		776	The underlying algorithm if subject to change, so currently these
		777	functions are not suitable for persistent hash tables, as their result
		778	value can change between diferent versions of libecb.
		779
		780	=over
		781
		782	=item uintptr_t ecb_ptrmix (void *ptr)
		783
		784	Mixes the bits of a pointer so the result is suitable for hash table
		785	lookups. In other words, this hashes the pointer value.
		786
		787	=item uintptr_t ecb_ptrmix (T *ptr) [C++]
		788
		789	Overload the C<ecb_ptrmix> function to work for any pointer in C++.
		790
		791	=item void *ecb_ptrunmix (uintptr_t v)
		792
		793	Unmix the hash value into the original pointer. This only works as long
		794	as the hash value is not truncated, i.e. you used C<uintptr_t> (or
		795	equivalent) throughout to store it.
		796
		797	=item T *ecb_ptrunmix<T> (uintptr_t v) [C++]
		798
		799	The somewhat less useful template version of C<ecb_ptrunmix> for
		800	C++. Example:
		801
		802	sometype *myptr;
		803	uintptr_t hash = ecb_ptrmix (myptr);
		804	sometype *orig = ecb_ptrunmix<sometype> (hash);
		805
		806	=item uint32_t ecb_mix32 (uint32_t v)
		807
		808	=item uint64_t ecb_mix64 (uint64_t v)
		809
		810	Sometimes you don't have a pointer but an integer whose values are very
		811	badly distributed. In this case you cna sue these integer versions of the
		812	mixing function. No C++ template is provided currently.
		813
		814	=item uint32_t ecb_unmix32 (uint32_t v)
		815
		816	=item uint64_t ecb_unmix64 (uint64_t v)
		817
		818	The reverse of the C<ecb_mix> functions - they take a mixed/hashed value
		819	and recover the original value.
		820
		821	=back
		822
		823	=head2 HOST ENDIANNESS CONVERSION
		824
		825	=over
		826
		827	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		828
		829	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		830
		831	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		832
		833	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		834
		835	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		836
		837	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		838
		839	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		840
		841	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		842	where C<be> and C<le> stand for big endian and little endian, respectively.
		843
		844	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		845
		846	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		847
		848	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		849
		850	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		851
		852	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		853
		854	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		855
		856	Like above, but converts I<from> host byte order to the specified
		857	endianness.
		858
		859	=back
		860
		861	In C++ the following additional template functions are supported:
		862
		863	=over
		864
		865	=item T ecb_be_to_host (T v)
		866
		867	=item T ecb_le_to_host (T v)
		868
		869	=item T ecb_host_to_be (T v)
		870
		871	=item T ecb_host_to_le (T v)
		872
		873	=back
		874
		875	These functions work like their C counterparts, above, but use templates,
		876	which make them useful in generic code.
		877
		878	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		879	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		880	again can be useful in generic code).
		881
		882	=head2 UNALIGNED LOAD/STORE
		883
		884	These function load or store unaligned multi-byte values.
		885
		886	=over
		887
		888	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		889
		890	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		891
		892	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		893
		894	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		895	memory.
		896
		897	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		898
		899	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		900
		901	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		902
		903	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		904
		905	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		906
		907	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		908
		909	Like above, but additionally convert from big endian (C<be>) or little
		910	endian (C<le>) byte order to host byte order while doing so.
		911
		912	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		913
		914	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		915
		916	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		917
		918	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		919	memory.
		920
		921	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		922
		923	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		924
		925	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		926
		927	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		928
		929	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		930
		931	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		932
		933	Like above, but additionally convert from host byte order to big endian
		934	(C<be>) or little endian (C<le>) byte order while doing so.
		935
		936	=back
		937
		938	In C++ the following additional template functions are supported:
		939
		940	=over
		941
		942	=item T ecb_peek<T> (const void *ptr)
		943
		944	=item T ecb_peek_be<T> (const void *ptr)
		945
		946	=item T ecb_peek_le<T> (const void *ptr)
		947
		948	=item T ecb_peek_u<T> (const void *ptr)
		949
		950	=item T ecb_peek_be_u<T> (const void *ptr)
		951
		952	=item T ecb_peek_le_u<T> (const void *ptr)
		953
		954	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		955	32 or 64 bit value from memory, with optional conversion from big/little
		956	endian.
		957
		958	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		959
		960	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		961
		962	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		963
		964	Unlike their C counterparts, these functions support 8 bit quantities
		965	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		966	all of which hopefully makes them more useful in generic code.
		967
		968	=item ecb_poke (void *ptr, T v)
		969
		970	=item ecb_poke_be (void *ptr, T v)
		971
		972	=item ecb_poke_le (void *ptr, T v)
		973
		974	=item ecb_poke_u (void *ptr, T v)
		975
		976	=item ecb_poke_be_u (void *ptr, T v)
		977
		978	=item ecb_poke_le_u (void *ptr, T v)
		979
		980	Again, similarly to their C counterparts, these functions store an
		981	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		982	big/little endian.
		983
		984	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		985
		986	Unlike their C counterparts, these functions support 8 bit quantities
		987	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		988	all of which hopefully makes them more useful in generic code.
		989
		990	=back
		991
		992	=head2 FAST INTEGER TO STRING
		993
		994	Libecb defines a set of very fast integer to decimal string (or integer
		995	to ascii, short C<i2a>) functions. These work by converting the integer
		996	to a fixed point representation and then successively multiplying out
		997	the topmost digits. Unlike some other, also very fast, libraries, ecb's
		998	algorithm should be completely branchless per digit, and does not rely on
		999	the presence of special cpu functions (such as clz).
		1000
		1001	There is a high level API that takes an C<int32_t>, C<uint32_t>,
		1002	C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
		1003	harder to use but supports slightly more formatting options.
		1004
		1005	=head3 HIGH LEVEL API
		1006
		1007	The high level API consists of four functions, one each for C<int32_t>,
		1008	C<uint32_t>, C<int64_t> and C<uint64_t>:
		1009
		1010	Example:
		1011
		1012	char buf[ECB_I2A_MAX_DIGITS + 1];
		1013	char *end = ecb_i2a_i32 (buf, 17262);
		1014	*end = 0;
		1015	// buf now contains "17262"
		1016
		1017	=over
		1018
		1019	=item ECB_I2A_I32_DIGITS (=11)
		1020
		1021	=item char ecb_i2a_u32 (char ptr, uint32_t value)
		1022
		1023	Takes an C<uint32_t> I<value> and formats it as a decimal number starting
		1024	at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
		1025	pointer to just after the generated string, where you would normally put
		1026	the terminating C<0> character. This function outputs the minimum number
		1027	of digits.
		1028
		1029	=item ECB_I2A_U32_DIGITS (=10)
		1030
		1031	=item char ecb_i2a_i32 (char ptr, int32_t value)
		1032
		1033	Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
		1034	sign if needed.
		1035
		1036	=item ECB_I2A_I64_DIGITS (=20)
		1037
		1038	=item char ecb_i2a_u64 (char ptr, uint64_t value)
		1039
		1040	=item ECB_I2A_U64_DIGITS (=21)
		1041
		1042	=item char ecb_i2a_i64 (char ptr, int64_t value)
		1043
		1044	Similar to their 32 bit counterparts, these take a 64 bit argument.
		1045
		1046	=item ECB_I2A_MAX_DIGITS (=21)
		1047
		1048	Instead of using a type specific length macro, you can just use
		1049	C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
		1050
		1051	=back
		1052
		1053	=head3 LOW-LEVEL API
		1054
		1055	The functions above use a number of low-level APIs which have some strict
		1056	limitations, but can be used as building blocks (studying C<ecb_i2a_i32>
		1057	and related functions is recommended).
		1058
		1059	There are three families of functions: functions that convert a number
		1060	to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
		1061	for "leading zeroes"), functions that generate up to N digits, skipping
		1062	leading zeroes (C<_N>), and functions that can generate more digits, but
		1063	the leading digit has limited range (C<_xN>).
		1064
		1065	None of the functions deal with negative numbers.
		1066
		1067	Example: convert an IP address in an u32 into dotted-quad:
		1068
		1069	uint32_t ip = 0x0a000164; // 10.0.1.100
		1070	char ips[3 * 4 + 3 + 1];
		1071	char *ptr = ips;
		1072	ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
		1073	ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
		1074	ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
		1075	ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
		1076	printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
		1077
		1078	=over
		1079
		1080	=item char ecb_i2a_02 (char ptr, uint32_t value) // 32 bit
		1081
		1082	=item char ecb_i2a_03 (char ptr, uint32_t value) // 32 bit
		1083
		1084	=item char ecb_i2a_04 (char ptr, uint32_t value) // 32 bit
		1085
		1086	=item char ecb_i2a_05 (char ptr, uint32_t value) // 64 bit
		1087
		1088	=item char ecb_i2a_06 (char ptr, uint32_t value) // 64 bit
		1089
		1090	=item char ecb_i2a_07 (char ptr, uint32_t value) // 64 bit
		1091
		1092	=item char ecb_i2a_08 (char ptr, uint32_t value) // 64 bit
		1093
		1094	=item char ecb_i2a_09 (char ptr, uint32_t value) // 64 bit
		1095
		1096	The C<< ecb_i2a_0I<N> >> functions take an unsigned I<value> and convert
		1097	them to exactly I<N> digits, returning a pointer to the first character
		1098	after the digits. The I<value> must be in range. The functions marked with
		1099	I<32 bit> do their calculations internally in 32 bit, the ones marked with
		1100	I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
		1101	architectures (the high level API decides on 32 vs. 64 bit versions using
		1102	C<ECB_64BIT_NATIVE>).
		1103
		1104	=item char ecb_i2a_2 (char ptr, uint32_t value) // 32 bit
		1105
		1106	=item char ecb_i2a_3 (char ptr, uint32_t value) // 32 bit
		1107
		1108	=item char ecb_i2a_4 (char ptr, uint32_t value) // 32 bit
		1109
		1110	=item char ecb_i2a_5 (char ptr, uint32_t value) // 64 bit
		1111
		1112	=item char ecb_i2a_6 (char ptr, uint32_t value) // 64 bit
		1113
		1114	=item char ecb_i2a_7 (char ptr, uint32_t value) // 64 bit
		1115
		1116	=item char ecb_i2a_8 (char ptr, uint32_t value) // 64 bit
		1117
		1118	=item char ecb_i2a_9 (char ptr, uint32_t value) // 64 bit
		1119
		1120	Similarly, the C<< ecb_i2a_I<N> >> functions take an unsigned I<value>
		1121	and convert them to at most I<N> digits, suppressing leading zeroes, and
		1122	returning a pointer to the first character after the digits.
		1123
		1124	=item ECB_I2A_MAX_X5 (=59074)
		1125
		1126	=item char ecb_i2a_x5 (char ptr, uint32_t value) // 32 bit
		1127
		1128	=item ECB_I2A_MAX_X10 (=2932500665)
		1129
		1130	=item char ecb_i2a_x10 (char ptr, uint32_t value) // 64 bit
		1131
		1132	The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >>
		1133	functions, but they can generate one digit more, as long as the number
		1134	is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
		1135	16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
		1136	respectively.
		1137
		1138	For example, the digit part of a 32 bit signed integer just fits into the
		1139	C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
		1140	digit number, it can convert all 32 bit signed numbers. Sadly, it's not
		1141	good enough for 32 bit unsigned numbers.
		1142
		1143	=back
		1144
		1145	=head2 FLOATING POINT FIDDLING
		1146
		1147	=over
		1148
		1149	=item ECB_INFINITY [-UECB_NO_LIBM]
		1150
		1151	Evaluates to positive infinity if supported by the platform, otherwise to
		1152	a truly huge number.
		1153
		1154	=item ECB_NAN [-UECB_NO_LIBM]
		1155
		1156	Evaluates to a quiet NAN if supported by the platform, otherwise to
		1157	C<ECB_INFINITY>.
		1158
		1159	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		1160
		1161	Same as C<ldexpf>, but always available.
		1162
		1163	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		1164
		1165	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		1166
		1167	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		1168
		1169	These functions each take an argument in the native C<float> or C<double>
		1170	type and return the IEEE 754 bit representation of it (binary16/half,
		1171	binary32/single or binary64/double precision).
		1172
		1173	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		1174	will be the most significant bit, followed by exponent and mantissa.
		1175
		1176	This function should work even when the native floating point format isn't
		1177	IEEE compliant, of course at a speed and code size penalty, and of course
		1178	also within reasonable limits (it tries to convert NaNs, infinities and
		1179	denormals, but will likely convert negative zero to positive zero).
		1180
		1181	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1182	be able to completely optimise away the 32 and 64 bit functions.
		1183
		1184	These functions can be helpful when serialising floats to the network - you
		1185	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		1186
		1187	Another use for these functions is to manipulate floating point values
		1188	directly.
		1189
		1190	Silly example: toggle the sign bit of a float.
		1191
		1192	/* On gcc-4.7 on amd64, */
		1193	/* this results in a single add instruction to toggle the bit, and 4 extra */
		1194	/* instructions to move the float value to an integer register and back. */
		1195
		1196	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		1197
		1198	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		1199
		1200	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		1201
		1202	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		1203
		1204	The reverse operation of the previous function - takes the bit
		1205	representation of an IEEE binary16, binary32 or binary64 number (half,
		1206	single or double precision) and converts it to the native C<float> or
		1207	C<double> format.
		1208
		1209	This function should work even when the native floating point format isn't
		1210	IEEE compliant, of course at a speed and code size penalty, and of course
		1211	also within reasonable limits (it tries to convert normals and denormals,
		1212	and might be lucky for infinities, and with extraordinary luck, also for
		1213	negative zero).
		1214
		1215	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1216	be able to optimise away this function completely.
		1217
		1218	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		1219
		1220	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		1221
		1222	Convert a IEEE binary32/single precision to binary16/half format, and vice
		1223	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1224	and NaNs) correctly.
		1225
		1226	These are functions are available under C<-DECB_NO_LIBM>, since
		1227	they do not rely on the platform floating point format. The
		1228	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1229	usually what you want.
408		1230
409	=back	1231	=back
410		1232
411	=head2 ARITHMETIC	1233	=head2 ARITHMETIC
412		1234
413	=over 4	1235	=over
414		1236
415	=item x = ecb_mod (m, n)	1237	=item x = ecb_mod (m, n)
416		1238
417	Returns the positive remainder of the modulo operation between C<m> and	1239	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1240	of the division operation between C<m> and C<n>, using floored
418	C<n>. Unlike the C modulo operator C<%>, this function ensures that the	1241	division. Unlike the C remainder operator C<%>, this function ensures that
419	return value is always positive).	1242	the return value is always positive and that the two numbers I<m> and
		1243	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1244	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1245	in the language.
420		1246
421	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	1247	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
422	negatable, that is, both C<m> and C<-m> must be representable in its	1248	negatable, that is, both C<m> and C<-m> must be representable in its
423	type.	1249	type (this typically excludes the minimum signed integer value, the same
		1250	limitation as for C</> and C<%> in C).
		1251
		1252	Current GCC/clang versions compile this into an efficient branchless
		1253	sequence on almost all CPUs.
		1254
		1255	For example, when you want to rotate forward through the members of an
		1256	array for increasing C<m> (which might be negative), then you should use
		1257	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1258	change direction for negative values:
		1259
		1260	for (m = -100; m <= 100; ++m)
		1261	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1262
		1263	=item x = ecb_div_rd (val, div)
		1264
		1265	=item x = ecb_div_ru (val, div)
		1266
		1267	Returns C<val> divided by C<div> rounded down or up, respectively.
		1268	C<val> and C<div> must have integer types and C<div> must be strictly
		1269	positive. Note that these functions are implemented with macros in C
		1270	and with function templates in C++.
424		1271
425	=back	1272	=back
426		1273
427	=head2 UTILITY	1274	=head2 UTILITY
428		1275
429	=over 4	1276	=over
430		1277
431	=item element_count = ecb_array_length (name) [MACRO]	1278	=item element_count = ecb_array_length (name)
432		1279
433	Returns the number of elements in the array C<name>. For example:	1280	Returns the number of elements in the array C<name>. For example:
434		1281
435	int primes[] = { 2, 3, 5, 7, 11 };	1282	int primes[] = { 2, 3, 5, 7, 11 };
436	int sum = 0;	1283	int sum = 0;
…		…
438	for (i = 0; i < ecb_array_length (primes); i++)	1285	for (i = 0; i < ecb_array_length (primes); i++)
439	sum += primes [i];	1286	sum += primes [i];
440		1287
441	=back	1288	=back
442		1289
		1290	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
443		1291
		1292	These symbols need to be defined before including F<ecb.h> the first time.
		1293
		1294	=over
		1295
		1296	=item ECB_NO_THREADS
		1297
		1298	If F<ecb.h> is never used from multiple threads, then this symbol can
		1299	be defined, in which case memory fences (and similar constructs) are
		1300	completely removed, leading to more efficient code and fewer dependencies.
		1301
		1302	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1303
		1304	=item ECB_NO_SMP
		1305
		1306	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1307	multiple threads, but never concurrently (e.g. if the system the program
		1308	runs on has only a single CPU with a single core, no hyperthreading and so
		1309	on), then this symbol can be defined, leading to more efficient code and
		1310	fewer dependencies.
		1311
		1312	=item ECB_NO_LIBM
		1313
		1314	When defined to C<1>, do not export any functions that might introduce
		1315	dependencies on the math library (usually called F<-lm>) - these are
		1316	marked with [-UECB_NO_LIBM].
		1317
		1318	=back
		1319
		1320	=head1 UNDOCUMENTED FUNCTIONALITY
		1321
		1322	F<ecb.h> is full of undocumented functionality as well, some of which is
		1323	intended to be internal-use only, some of which we forgot to document, and
		1324	some of which we hide because we are not sure we will keep the interface
		1325	stable.
		1326
		1327	While you are welcome to rummage around and use whatever you find useful
		1328	(we don't want to stop you), keep in mind that we will change undocumented
		1329	functionality in incompatible ways without thinking twice, while we are
		1330	considerably more conservative with documented things.
		1331
		1332	=head1 AUTHORS
		1333
		1334	C<libecb> is designed and maintained by:
		1335
		1336	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1337	Marc Alexander Lehmann <schmorp@schmorp.de>

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Comparing libecb/ecb.pod (file contents): Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs. Revision 1.101 by root, Mon Nov 22 17:15:50 2021 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.101 by root, Mon Nov 22 17:15:50 2021 UTC