[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 1.103 by root, Wed Mar 23 09:59:49 2022 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	=item uint_fast8_t ecb_gray8_encode (uint_fast8_t b)
		754
		755	=item uint_fast16_t ecb_gray16_encode (uint_fast16_t b)
		756
		757	=item uint_fast32_t ecb_gray32_encode (uint_fast32_t b)
		758
		759	=item uint_fast64_t ecb_gray64_encode (uint_fast64_t b)
		760
		761	Encode an unsigned into its corresponding (reflective) gray code - the
		762	kind of gray code meant when just talking about "gray code". These
		763	functions are very fast and all have identical implementation, so there is
		764	no need to use a smaller type, as long as your CPU can handle it natively.
		765
		766	=item T ecb_gray_encode (T b) [C++]
		767
		768	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		769
		770	=item uint_fast8_t ecb_gray8_decode (uint_fast8_t b)
		771
		772	=item uint_fast16_t ecb_gray16_decode (uint_fast16_t b)
		773
		774	=item uint_fast32_t ecb_gray32_decode (uint_fast32_t b)
		775
		776	=item uint_fast64_t ecb_gray64_decode (uint_fast64_t b)
		777
		778	Decode a gray code back into linear index form (the reverse of
		779	C<ecb_gray*_encode>. Unlike the encode functions, the decode functions
		780	have higher time complexity for larger types, so it can pay off to use a
		781	smaller type here.
		782
		783	=item T ecb_gray_decode (T b) [C++]
		784
		785	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		786
		787	=back
		788
		789	=head2 BIT MIXING, HASHING
		790
		791	Sometimes you have an integer and want to distribute its bits well, for
		792	example, to use it as a hash in a hashtable. A common example is pointer
		793	values, which often only have a limited range (e.g. low and high bits are
		794	often zero).
		795
		796	The following functions try to mix the bits to get a good bias-free
		797	distribution. They were mainly made for pointers, but the underlying
		798	integer functions are exposed as well.
		799
		800	As an added benefit, the functions are reversible, so if you find it
		801	convenient to store only the hash value, you can recover the original
		802	pointer from the hash ("unmix"), as long as your pinters are 32 or 64 bit
		803	(if this isn't the case on your platform, drop us a note and we will add
		804	functions for other bit widths).
		805
		806	The unmix functions are very slightly slower than the mix functions, so
		807	it is equally very slightly preferable to store the original values wehen
		808	convenient.
		809
		810	The underlying algorithm if subject to change, so currently these
		811	functions are not suitable for persistent hash tables, as their result
		812	value can change between diferent versions of libecb.
		813
		814	=over
		815
		816	=item uintptr_t ecb_ptrmix (void *ptr)
		817
		818	Mixes the bits of a pointer so the result is suitable for hash table
		819	lookups. In other words, this hashes the pointer value.
		820
		821	=item uintptr_t ecb_ptrmix (T *ptr) [C++]
		822
		823	Overload the C<ecb_ptrmix> function to work for any pointer in C++.
		824
		825	=item void *ecb_ptrunmix (uintptr_t v)
		826
		827	Unmix the hash value into the original pointer. This only works as long
		828	as the hash value is not truncated, i.e. you used C<uintptr_t> (or
		829	equivalent) throughout to store it.
		830
		831	=item T *ecb_ptrunmix<T> (uintptr_t v) [C++]
		832
		833	The somewhat less useful template version of C<ecb_ptrunmix> for
		834	C++. Example:
		835
		836	sometype *myptr;
		837	uintptr_t hash = ecb_ptrmix (myptr);
		838	sometype *orig = ecb_ptrunmix<sometype> (hash);
		839
		840	=item uint32_t ecb_mix32 (uint32_t v)
		841
		842	=item uint64_t ecb_mix64 (uint64_t v)
		843
		844	Sometimes you don't have a pointer but an integer whose values are very
		845	badly distributed. In this case you cna sue these integer versions of the
		846	mixing function. No C++ template is provided currently.
		847
		848	=item uint32_t ecb_unmix32 (uint32_t v)
		849
		850	=item uint64_t ecb_unmix64 (uint64_t v)
		851
		852	The reverse of the C<ecb_mix> functions - they take a mixed/hashed value
		853	and recover the original value.
		854
		855	=back
		856
		857	=head2 HOST ENDIANNESS CONVERSION
		858
		859	=over
		860
		861	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		862
		863	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		864
		865	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		866
		867	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		868
		869	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		870
		871	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		872
		873	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		874
		875	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		876	where C<be> and C<le> stand for big endian and little endian, respectively.
		877
		878	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		879
		880	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		881
		882	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		883
		884	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		885
		886	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		887
		888	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		889
		890	Like above, but converts I<from> host byte order to the specified
		891	endianness.
		892
		893	=back
		894
		895	In C++ the following additional template functions are supported:
		896
		897	=over
		898
		899	=item T ecb_be_to_host (T v)
		900
		901	=item T ecb_le_to_host (T v)
		902
		903	=item T ecb_host_to_be (T v)
		904
		905	=item T ecb_host_to_le (T v)
		906
		907	=back
		908
		909	These functions work like their C counterparts, above, but use templates,
		910	which make them useful in generic code.
		911
		912	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		913	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		914	again can be useful in generic code).
		915
		916	=head2 UNALIGNED LOAD/STORE
		917
		918	These function load or store unaligned multi-byte values.
		919
		920	=over
		921
		922	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		923
		924	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		925
		926	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		927
		928	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		929	memory.
		930
		931	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		932
		933	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		934
		935	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		936
		937	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		938
		939	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		940
		941	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		942
		943	Like above, but additionally convert from big endian (C<be>) or little
		944	endian (C<le>) byte order to host byte order while doing so.
		945
		946	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		947
		948	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		949
		950	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		951
		952	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		953	memory.
		954
		955	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		956
		957	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		958
		959	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		960
		961	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		962
		963	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		964
		965	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		966
		967	Like above, but additionally convert from host byte order to big endian
		968	(C<be>) or little endian (C<le>) byte order while doing so.
		969
		970	=back
		971
		972	In C++ the following additional template functions are supported:
		973
		974	=over
		975
		976	=item T ecb_peek<T> (const void *ptr)
		977
		978	=item T ecb_peek_be<T> (const void *ptr)
		979
		980	=item T ecb_peek_le<T> (const void *ptr)
		981
		982	=item T ecb_peek_u<T> (const void *ptr)
		983
		984	=item T ecb_peek_be_u<T> (const void *ptr)
		985
		986	=item T ecb_peek_le_u<T> (const void *ptr)
		987
		988	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		989	32 or 64 bit value from memory, with optional conversion from big/little
		990	endian.
		991
		992	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		993
		994	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		995
		996	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		997
		998	Unlike their C counterparts, these functions support 8 bit quantities
		999	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		1000	all of which hopefully makes them more useful in generic code.
		1001
		1002	=item ecb_poke (void *ptr, T v)
		1003
		1004	=item ecb_poke_be (void *ptr, T v)
		1005
		1006	=item ecb_poke_le (void *ptr, T v)
		1007
		1008	=item ecb_poke_u (void *ptr, T v)
		1009
		1010	=item ecb_poke_be_u (void *ptr, T v)
		1011
		1012	=item ecb_poke_le_u (void *ptr, T v)
		1013
		1014	Again, similarly to their C counterparts, these functions store an
		1015	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		1016	big/little endian.
		1017
		1018	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		1019
		1020	Unlike their C counterparts, these functions support 8 bit quantities
		1021	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		1022	all of which hopefully makes them more useful in generic code.
		1023
		1024	=back
		1025
		1026	=head2 FAST INTEGER TO STRING
		1027
		1028	Libecb defines a set of very fast integer to decimal string (or integer
		1029	to ascii, short C<i2a>) functions. These work by converting the integer
		1030	to a fixed point representation and then successively multiplying out
		1031	the topmost digits. Unlike some other, also very fast, libraries, ecb's
		1032	algorithm should be completely branchless per digit, and does not rely on
		1033	the presence of special cpu functions (such as clz).
		1034
		1035	There is a high level API that takes an C<int32_t>, C<uint32_t>,
		1036	C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
		1037	harder to use but supports slightly more formatting options.
		1038
		1039	=head3 HIGH LEVEL API
		1040
		1041	The high level API consists of four functions, one each for C<int32_t>,
		1042	C<uint32_t>, C<int64_t> and C<uint64_t>:
		1043
		1044	Example:
		1045
		1046	char buf[ECB_I2A_MAX_DIGITS + 1];
		1047	char *end = ecb_i2a_i32 (buf, 17262);
		1048	*end = 0;
		1049	// buf now contains "17262"
		1050
		1051	=over
		1052
		1053	=item ECB_I2A_I32_DIGITS (=11)
		1054
		1055	=item char ecb_i2a_u32 (char ptr, uint32_t value)
		1056
		1057	Takes an C<uint32_t> I<value> and formats it as a decimal number starting
		1058	at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
		1059	pointer to just after the generated string, where you would normally put
		1060	the terminating C<0> character. This function outputs the minimum number
		1061	of digits.
		1062
		1063	=item ECB_I2A_U32_DIGITS (=10)
		1064
		1065	=item char ecb_i2a_i32 (char ptr, int32_t value)
		1066
		1067	Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
		1068	sign if needed.
		1069
		1070	=item ECB_I2A_I64_DIGITS (=20)
		1071
		1072	=item char ecb_i2a_u64 (char ptr, uint64_t value)
		1073
		1074	=item ECB_I2A_U64_DIGITS (=21)
		1075
		1076	=item char ecb_i2a_i64 (char ptr, int64_t value)
		1077
		1078	Similar to their 32 bit counterparts, these take a 64 bit argument.
		1079
		1080	=item ECB_I2A_MAX_DIGITS (=21)
		1081
		1082	Instead of using a type specific length macro, you can just use
		1083	C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
		1084
		1085	=back
		1086
		1087	=head3 LOW-LEVEL API
		1088
		1089	The functions above use a number of low-level APIs which have some strict
		1090	limitations, but can be used as building blocks (studying C<ecb_i2a_i32>
		1091	and related functions is recommended).
		1092
		1093	There are three families of functions: functions that convert a number
		1094	to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
		1095	for "leading zeroes"), functions that generate up to N digits, skipping
		1096	leading zeroes (C<_N>), and functions that can generate more digits, but
		1097	the leading digit has limited range (C<_xN>).
		1098
		1099	None of the functions deal with negative numbers.
		1100
		1101	Example: convert an IP address in an u32 into dotted-quad:
		1102
		1103	uint32_t ip = 0x0a000164; // 10.0.1.100
		1104	char ips[3 * 4 + 3 + 1];
		1105	char *ptr = ips;
		1106	ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
		1107	ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
		1108	ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
		1109	ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
		1110	printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
		1111
		1112	=over
		1113
		1114	=item char ecb_i2a_02 (char ptr, uint32_t value) // 32 bit
		1115
		1116	=item char ecb_i2a_03 (char ptr, uint32_t value) // 32 bit
		1117
		1118	=item char ecb_i2a_04 (char ptr, uint32_t value) // 32 bit
		1119
		1120	=item char ecb_i2a_05 (char ptr, uint32_t value) // 64 bit
		1121
		1122	=item char ecb_i2a_06 (char ptr, uint32_t value) // 64 bit
		1123
		1124	=item char ecb_i2a_07 (char ptr, uint32_t value) // 64 bit
		1125
		1126	=item char ecb_i2a_08 (char ptr, uint32_t value) // 64 bit
		1127
		1128	=item char ecb_i2a_09 (char ptr, uint32_t value) // 64 bit
		1129
		1130	The C<< ecb_i2a_0I<N> >> functions take an unsigned I<value> and convert
		1131	them to exactly I<N> digits, returning a pointer to the first character
		1132	after the digits. The I<value> must be in range. The functions marked with
		1133	I<32 bit> do their calculations internally in 32 bit, the ones marked with
		1134	I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
		1135	architectures (the high level API decides on 32 vs. 64 bit versions using
		1136	C<ECB_64BIT_NATIVE>).
		1137
		1138	=item char ecb_i2a_2 (char ptr, uint32_t value) // 32 bit
		1139
		1140	=item char ecb_i2a_3 (char ptr, uint32_t value) // 32 bit
		1141
		1142	=item char ecb_i2a_4 (char ptr, uint32_t value) // 32 bit
		1143
		1144	=item char ecb_i2a_5 (char ptr, uint32_t value) // 64 bit
		1145
		1146	=item char ecb_i2a_6 (char ptr, uint32_t value) // 64 bit
		1147
		1148	=item char ecb_i2a_7 (char ptr, uint32_t value) // 64 bit
		1149
		1150	=item char ecb_i2a_8 (char ptr, uint32_t value) // 64 bit
		1151
		1152	=item char ecb_i2a_9 (char ptr, uint32_t value) // 64 bit
		1153
		1154	Similarly, the C<< ecb_i2a_I<N> >> functions take an unsigned I<value>
		1155	and convert them to at most I<N> digits, suppressing leading zeroes, and
		1156	returning a pointer to the first character after the digits.
		1157
		1158	=item ECB_I2A_MAX_X5 (=59074)
		1159
		1160	=item char ecb_i2a_x5 (char ptr, uint32_t value) // 32 bit
		1161
		1162	=item ECB_I2A_MAX_X10 (=2932500665)
		1163
		1164	=item char ecb_i2a_x10 (char ptr, uint32_t value) // 64 bit
		1165
		1166	The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >>
		1167	functions, but they can generate one digit more, as long as the number
		1168	is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
		1169	16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
		1170	respectively.
		1171
		1172	For example, the digit part of a 32 bit signed integer just fits into the
		1173	C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
		1174	digit number, it can convert all 32 bit signed numbers. Sadly, it's not
		1175	good enough for 32 bit unsigned numbers.
		1176
		1177	=back
		1178
		1179	=head2 FLOATING POINT FIDDLING
		1180
		1181	=over
		1182
		1183	=item ECB_INFINITY [-UECB_NO_LIBM]
		1184
		1185	Evaluates to positive infinity if supported by the platform, otherwise to
		1186	a truly huge number.
		1187
		1188	=item ECB_NAN [-UECB_NO_LIBM]
		1189
		1190	Evaluates to a quiet NAN if supported by the platform, otherwise to
		1191	C<ECB_INFINITY>.
		1192
		1193	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		1194
		1195	Same as C<ldexpf>, but always available.
		1196
		1197	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		1198
		1199	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		1200
		1201	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		1202
		1203	These functions each take an argument in the native C<float> or C<double>
		1204	type and return the IEEE 754 bit representation of it (binary16/half,
		1205	binary32/single or binary64/double precision).
		1206
		1207	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		1208	will be the most significant bit, followed by exponent and mantissa.
		1209
		1210	This function should work even when the native floating point format isn't
		1211	IEEE compliant, of course at a speed and code size penalty, and of course
		1212	also within reasonable limits (it tries to convert NaNs, infinities and
		1213	denormals, but will likely convert negative zero to positive zero).
		1214
		1215	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1216	be able to completely optimise away the 32 and 64 bit functions.
		1217
		1218	These functions can be helpful when serialising floats to the network - you
		1219	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		1220
		1221	Another use for these functions is to manipulate floating point values
		1222	directly.
		1223
		1224	Silly example: toggle the sign bit of a float.
		1225
		1226	/* On gcc-4.7 on amd64, */
		1227	/* this results in a single add instruction to toggle the bit, and 4 extra */
		1228	/* instructions to move the float value to an integer register and back. */
		1229
		1230	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		1231
		1232	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		1233
		1234	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		1235
		1236	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		1237
		1238	The reverse operation of the previous function - takes the bit
		1239	representation of an IEEE binary16, binary32 or binary64 number (half,
		1240	single or double precision) and converts it to the native C<float> or
		1241	C<double> format.
		1242
		1243	This function should work even when the native floating point format isn't
		1244	IEEE compliant, of course at a speed and code size penalty, and of course
		1245	also within reasonable limits (it tries to convert normals and denormals,
		1246	and might be lucky for infinities, and with extraordinary luck, also for
		1247	negative zero).
		1248
		1249	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1250	be able to optimise away this function completely.
		1251
		1252	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		1253
		1254	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		1255
		1256	Convert a IEEE binary32/single precision to binary16/half format, and vice
		1257	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1258	and NaNs) correctly.
		1259
		1260	These are functions are available under C<-DECB_NO_LIBM>, since
		1261	they do not rely on the platform floating point format. The
		1262	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1263	usually what you want.
408		1264
409	=back	1265	=back
410		1266
411	=head2 ARITHMETIC	1267	=head2 ARITHMETIC
412		1268
413	=over 4	1269	=over
414		1270
415	=item x = ecb_mod (m, n)	1271	=item x = ecb_mod (m, n)
416		1272
417	Returns the positive remainder of the modulo operation between C<m> and	1273	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1274	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	1275	division. Unlike the C remainder operator C<%>, this function ensures that
419	return value is always positive).	1276	the return value is always positive and that the two numbers I<m> and
		1277	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1278	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1279	in the language.
420		1280
421	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	1281	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	1282	negatable, that is, both C<m> and C<-m> must be representable in its
423	type.	1283	type (this typically excludes the minimum signed integer value, the same
		1284	limitation as for C</> and C<%> in C).
		1285
		1286	Current GCC/clang versions compile this into an efficient branchless
		1287	sequence on almost all CPUs.
		1288
		1289	For example, when you want to rotate forward through the members of an
		1290	array for increasing C<m> (which might be negative), then you should use
		1291	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1292	change direction for negative values:
		1293
		1294	for (m = -100; m <= 100; ++m)
		1295	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1296
		1297	=item x = ecb_div_rd (val, div)
		1298
		1299	=item x = ecb_div_ru (val, div)
		1300
		1301	Returns C<val> divided by C<div> rounded down or up, respectively.
		1302	C<val> and C<div> must have integer types and C<div> must be strictly
		1303	positive. Note that these functions are implemented with macros in C
		1304	and with function templates in C++.
424		1305
425	=back	1306	=back
426		1307
427	=head2 UTILITY	1308	=head2 UTILITY
428		1309
429	=over 4	1310	=over
430		1311
431	=item element_count = ecb_array_length (name) [MACRO]	1312	=item element_count = ecb_array_length (name)
432		1313
433	Returns the number of elements in the array C<name>. For example:	1314	Returns the number of elements in the array C<name>. For example:
434		1315
435	int primes[] = { 2, 3, 5, 7, 11 };	1316	int primes[] = { 2, 3, 5, 7, 11 };
436	int sum = 0;	1317	int sum = 0;
…		…
438	for (i = 0; i < ecb_array_length (primes); i++)	1319	for (i = 0; i < ecb_array_length (primes); i++)
439	sum += primes [i];	1320	sum += primes [i];
440		1321
441	=back	1322	=back
442		1323
		1324	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
443		1325
		1326	These symbols need to be defined before including F<ecb.h> the first time.
		1327
		1328	=over
		1329
		1330	=item ECB_NO_THREADS
		1331
		1332	If F<ecb.h> is never used from multiple threads, then this symbol can
		1333	be defined, in which case memory fences (and similar constructs) are
		1334	completely removed, leading to more efficient code and fewer dependencies.
		1335
		1336	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1337
		1338	=item ECB_NO_SMP
		1339
		1340	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1341	multiple threads, but never concurrently (e.g. if the system the program
		1342	runs on has only a single CPU with a single core, no hyperthreading and so
		1343	on), then this symbol can be defined, leading to more efficient code and
		1344	fewer dependencies.
		1345
		1346	=item ECB_NO_LIBM
		1347
		1348	When defined to C<1>, do not export any functions that might introduce
		1349	dependencies on the math library (usually called F<-lm>) - these are
		1350	marked with [-UECB_NO_LIBM].
		1351
		1352	=back
		1353
		1354	=head1 UNDOCUMENTED FUNCTIONALITY
		1355
		1356	F<ecb.h> is full of undocumented functionality as well, some of which is
		1357	intended to be internal-use only, some of which we forgot to document, and
		1358	some of which we hide because we are not sure we will keep the interface
		1359	stable.
		1360
		1361	While you are welcome to rummage around and use whatever you find useful
		1362	(we don't want to stop you), keep in mind that we will change undocumented
		1363	functionality in incompatible ways without thinking twice, while we are
		1364	considerably more conservative with documented things.
		1365
		1366	=head1 AUTHORS
		1367
		1368	C<libecb> is designed and maintained by:
		1369
		1370	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1371	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 1.103 by root, Wed Mar 23 09:59:49 2022 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 1.103 by root, Wed Mar 23 09:59:49 2022 UTC