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Revision 1.17 by root, Thu May 26 23:55:58 2011 UTC vs.
Revision 1.95 by root, Sun Aug 1 10:00:33 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 isn'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 HOST ENDIANNESS CONVERSION
		756
		757	=over
		758
		759	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		760
		761	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		762
		763	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		764
		765	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		766
		767	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		768
		769	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		770
		771	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		772
		773	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		774	where C<be> and C<le> stand for big endian and little endian, respectively.
		775
		776	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		777
		778	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		779
		780	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		781
		782	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		783
		784	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		785
		786	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		787
		788	Like above, but converts I<from> host byte order to the specified
		789	endianness.
		790
		791	=back
		792
		793	In C++ the following additional template functions are supported:
		794
		795	=over
		796
		797	=item T ecb_be_to_host (T v)
		798
		799	=item T ecb_le_to_host (T v)
		800
		801	=item T ecb_host_to_be (T v)
		802
		803	=item T ecb_host_to_le (T v)
		804
		805	=back
		806
		807	These functions work like their C counterparts, above, but use templates,
		808	which make them useful in generic code.
		809
		810	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		811	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		812	again can be useful in generic code).
		813
		814	=head2 UNALIGNED LOAD/STORE
		815
		816	These function load or store unaligned multi-byte values.
		817
		818	=over
		819
		820	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		821
		822	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		823
		824	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		825
		826	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		827	memory.
		828
		829	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		830
		831	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		832
		833	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		834
		835	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		836
		837	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		838
		839	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		840
		841	Like above, but additionally convert from big endian (C<be>) or little
		842	endian (C<le>) byte order to host byte order while doing so.
		843
		844	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		845
		846	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		847
		848	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		849
		850	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		851	memory.
		852
		853	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		854
		855	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		856
		857	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		858
		859	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		860
		861	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		862
		863	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		864
		865	Like above, but additionally convert from host byte order to big endian
		866	(C<be>) or little endian (C<le>) byte order while doing so.
		867
		868	=back
		869
		870	In C++ the following additional template functions are supported:
		871
		872	=over
		873
		874	=item T ecb_peek<T> (const void *ptr)
		875
		876	=item T ecb_peek_be<T> (const void *ptr)
		877
		878	=item T ecb_peek_le<T> (const void *ptr)
		879
		880	=item T ecb_peek_u<T> (const void *ptr)
		881
		882	=item T ecb_peek_be_u<T> (const void *ptr)
		883
		884	=item T ecb_peek_le_u<T> (const void *ptr)
		885
		886	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		887	32 or 64 bit value from memory, with optional conversion from big/little
		888	endian.
		889
		890	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		891
		892	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		893
		894	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		895
		896	Unlike their C counterparts, these functions support 8 bit quantities
		897	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		898	all of which hopefully makes them more useful in generic code.
		899
		900	=item ecb_poke (void *ptr, T v)
		901
		902	=item ecb_poke_be (void *ptr, T v)
		903
		904	=item ecb_poke_le (void *ptr, T v)
		905
		906	=item ecb_poke_u (void *ptr, T v)
		907
		908	=item ecb_poke_be_u (void *ptr, T v)
		909
		910	=item ecb_poke_le_u (void *ptr, T v)
		911
		912	Again, similarly to their C counterparts, these functions store an
		913	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		914	big/little endian.
		915
		916	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		917
		918	Unlike their C counterparts, these functions support 8 bit quantities
		919	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		920	all of which hopefully makes them more useful in generic code.
		921
		922	=back
		923
		924	=head2 FAST INTEGER TO STRING
		925
		926	Libecb defines a set of very fast integer to decimal string (or integer
		927	to ascii, short C<i2a>) functions. These work by converting the integer
		928	to a fixed point representation and then successively multiplying out
		929	the topmost digits. Unlike some other, also very fast, libraries, ecb's
		930	algorithm should be completely branchless per digit, and does not rely on
		931	the presence of special cpu functions (such as clz).
		932
		933	There is a high level API that takes an C<int32_t>, C<uint32_t>,
		934	C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
		935	harder to use but supports slightly more formatting options.
		936
		937	=head3 HIGH LEVEL API
		938
		939	The high level API consists of four functions, one each for C<int32_t>,
		940	C<uint32_t>, C<int64_t> and C<uint64_t>:
		941
		942	Example:
		943
		944	char buf[ECB_I2A_MAX_DIGITS + 1];
		945	char *end = ecb_i2a_i32 (buf, 17262);
		946	*end = 0;
		947	// buf now contains "17262"
		948
		949	=over
		950
		951	=item ECB_I2A_I32_DIGITS (=11)
		952
		953	=item char ecb_i2a_u32 (char ptr, uint32_t value)
		954
		955	Takes an C<uint32_t> I<value> and formats it as a decimal number starting
		956	at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
		957	pointer to just after the generated string, where you would normally put
		958	the terminating C<0> character. This function outputs the minimum number
		959	of digits.
		960
		961	=item ECB_I2A_U32_DIGITS (=10)
		962
		963	=item char ecb_i2a_i32 (char ptr, int32_t value)
		964
		965	Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
		966	sign if needed.
		967
		968	=item ECB_I2A_I64_DIGITS (=20)
		969
		970	=item char ecb_i2a_u64 (char ptr, uint64_t value)
		971
		972	=item ECB_I2A_U64_DIGITS (=21)
		973
		974	=item char ecb_i2a_i64 (char ptr, int64_t value)
		975
		976	Similar to their 32 bit counterparts, these take a 64 bit argument.
		977
		978	=item ECB_I2A_MAX_DIGITS (=21)
		979
		980	Instead of using a type specific length macro, youi can just use
		981	C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
		982
		983	=back
		984
		985	=head3 LOW-LEVEL API
		986
		987	The functions above use a number of low-level APIs which have some strict
		988	limitations, but can be used as building blocks (study of C<ecb_i2a_i32>
		989	and related functions is recommended).
		990
		991	There are three families of functions: functions that convert a number
		992	to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
		993	for "leading zeroes"), functions that generate up to N digits, skipping
		994	leading zeroes (C<_N>), and functions that can generate more digits, but
		995	the leading digit has limited range (C<_xN>).
		996
		997	None of the functions deal with negative numbers.
		998
		999	Example: convert an IP address in an u32 into dotted-quad:
		1000
		1001	uint32_t ip = 0x0a000164; // 10.0.1.100
		1002	char ips[3 * 4 + 3 + 1];
		1003	char *ptr = ips;
		1004	ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
		1005	ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
		1006	ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
		1007	ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
		1008	printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
		1009
		1010	=over
		1011
		1012	=item char ecb_i2a_02 (char ptr, uint32_t value) // 32 bit
		1013
		1014	=item char ecb_i2a_03 (char ptr, uint32_t value) // 32 bit
		1015
		1016	=item char ecb_i2a_04 (char ptr, uint32_t value) // 32 bit
		1017
		1018	=item char ecb_i2a_05 (char ptr, uint32_t value) // 64 bit
		1019
		1020	=item char ecb_i2a_06 (char ptr, uint32_t value) // 64 bit
		1021
		1022	=item char ecb_i2a_07 (char ptr, uint32_t value) // 64 bit
		1023
		1024	=item char ecb_i2a_08 (char ptr, uint32_t value) // 64 bit
		1025
		1026	=item char ecb_i2a_09 (char ptr, uint32_t value) // 64 bit
		1027
		1028	The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert
		1029	them to exactly I<N> digits, returning a pointer to the first character
		1030	after the digits. The I<value> must be in range. The functions marked with
		1031	I<32 bit> do their calculations internally in 32 bit, the ones marked with
		1032	I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
		1033	architectures (the high level API decides on 32 vs. 64 bit versions using
		1034	C<ECB_64BIT_NATIVE>).
		1035
		1036	=item char ecb_i2a_2 (char ptr, uint32_t value) // 32 bit
		1037
		1038	=item char ecb_i2a_3 (char ptr, uint32_t value) // 32 bit
		1039
		1040	=item char ecb_i2a_4 (char ptr, uint32_t value) // 32 bit
		1041
		1042	=item char ecb_i2a_5 (char ptr, uint32_t value) // 64 bit
		1043
		1044	=item char ecb_i2a_6 (char ptr, uint32_t value) // 64 bit
		1045
		1046	=item char ecb_i2a_7 (char ptr, uint32_t value) // 64 bit
		1047
		1048	=item char ecb_i2a_8 (char ptr, uint32_t value) // 64 bit
		1049
		1050	=item char ecb_i2a_9 (char ptr, uint32_t value) // 64 bit
		1051
		1052	Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value>
		1053	and convert them to at most I<N> digits, suppressing leading zeroes, and
		1054	returning a pointer to the first character after the digits.
		1055
		1056	=item ECB_I2A_MAX_X5 (=59074)
		1057
		1058	=item char ecb_i2a_x5 (char ptr, uint32_t value) // 32 bit
		1059
		1060	=item ECB_I2A_MAX_X10 (=2932500665)
		1061
		1062	=item char ecb_i2a_x10 (char ptr, uint32_t value) // 64 bit
		1063
		1064	The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >
		1065	functions, but they can generate one digit more, as long as the number
		1066	is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
		1067	16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
		1068	respectively.
		1069
		1070	For example, the digit part of a 32 bit signed integer just fits into the
		1071	C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
		1072	digit number, it can convert all 32 bit signed numbers. Sadly, it's not
		1073	good enough for 32 bit unsigned numbers.
		1074
		1075	=back
		1076
		1077	=head2 FLOATING POINT FIDDLING
		1078
		1079	=over
		1080
		1081	=item ECB_INFINITY [-UECB_NO_LIBM]
		1082
		1083	Evaluates to positive infinity if supported by the platform, otherwise to
		1084	a truly huge number.
		1085
		1086	=item ECB_NAN [-UECB_NO_LIBM]
		1087
		1088	Evaluates to a quiet NAN if supported by the platform, otherwise to
		1089	C<ECB_INFINITY>.
		1090
		1091	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		1092
		1093	Same as C<ldexpf>, but always available.
		1094
		1095	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		1096
		1097	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		1098
		1099	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		1100
		1101	These functions each take an argument in the native C<float> or C<double>
		1102	type and return the IEEE 754 bit representation of it (binary16/half,
		1103	binary32/single or binary64/double precision).
		1104
		1105	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		1106	will be the most significant bit, followed by exponent and mantissa.
		1107
		1108	This function should work even when the native floating point format isn't
		1109	IEEE compliant, of course at a speed and code size penalty, and of course
		1110	also within reasonable limits (it tries to convert NaNs, infinities and
		1111	denormals, but will likely convert negative zero to positive zero).
		1112
		1113	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1114	be able to optimise away this function completely.
		1115
		1116	These functions can be helpful when serialising floats to the network - you
		1117	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		1118
		1119	Another use for these functions is to manipulate floating point values
		1120	directly.
		1121
		1122	Silly example: toggle the sign bit of a float.
		1123
		1124	/* On gcc-4.7 on amd64, */
		1125	/* this results in a single add instruction to toggle the bit, and 4 extra */
		1126	/* instructions to move the float value to an integer register and back. */
		1127
		1128	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		1129
		1130	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		1131
		1132	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		1133
		1134	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		1135
		1136	The reverse operation of the previous function - takes the bit
		1137	representation of an IEEE binary16, binary32 or binary64 number (half,
		1138	single or double precision) and converts it to the native C<float> or
		1139	C<double> format.
		1140
		1141	This function should work even when the native floating point format isn't
		1142	IEEE compliant, of course at a speed and code size penalty, and of course
		1143	also within reasonable limits (it tries to convert normals and denormals,
		1144	and might be lucky for infinities, and with extraordinary luck, also for
		1145	negative zero).
		1146
		1147	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1148	be able to optimise away this function completely.
		1149
		1150	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		1151
		1152	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		1153
		1154	Convert a IEEE binary32/single precision to binary16/half format, and vice
		1155	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1156	and NaNs) correctly.
		1157
		1158	These are functions are available under C<-DECB_NO_LIBM>, since
		1159	they do not rely on the platform floating point format. The
		1160	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1161	usually what you want.
408		1162
409	=back	1163	=back
410		1164
411	=head2 ARITHMETIC	1165	=head2 ARITHMETIC
412		1166
413	=over 4	1167	=over
414		1168
415	=item x = ecb_mod (m, n)	1169	=item x = ecb_mod (m, n)
416		1170
417	Returns the positive remainder of the modulo operation between C<m> and	1171	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1172	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	1173	division. Unlike the C remainder operator C<%>, this function ensures that
419	return value is always positive).	1174	the return value is always positive and that the two numbers I<m> and
		1175	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1176	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1177	in the language.
420		1178
421	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	1179	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	1180	negatable, that is, both C<m> and C<-m> must be representable in its
423	type.	1181	type (this typically excludes the minimum signed integer value, the same
		1182	limitation as for C</> and C<%> in C).
		1183
		1184	Current GCC/clang versions compile this into an efficient branchless
		1185	sequence on almost all CPUs.
		1186
		1187	For example, when you want to rotate forward through the members of an
		1188	array for increasing C<m> (which might be negative), then you should use
		1189	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1190	change direction for negative values:
		1191
		1192	for (m = -100; m <= 100; ++m)
		1193	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1194
		1195	=item x = ecb_div_rd (val, div)
		1196
		1197	=item x = ecb_div_ru (val, div)
		1198
		1199	Returns C<val> divided by C<div> rounded down or up, respectively.
		1200	C<val> and C<div> must have integer types and C<div> must be strictly
		1201	positive. Note that these functions are implemented with macros in C
		1202	and with function templates in C++.
424		1203
425	=back	1204	=back
426		1205
427	=head2 UTILITY	1206	=head2 UTILITY
428		1207
429	=over 4	1208	=over
430		1209
431	=item element_count = ecb_array_length (name) [MACRO]	1210	=item element_count = ecb_array_length (name)
432		1211
433	Returns the number of elements in the array C<name>. For example:	1212	Returns the number of elements in the array C<name>. For example:
434		1213
435	int primes[] = { 2, 3, 5, 7, 11 };	1214	int primes[] = { 2, 3, 5, 7, 11 };
436	int sum = 0;	1215	int sum = 0;
…		…
438	for (i = 0; i < ecb_array_length (primes); i++)	1217	for (i = 0; i < ecb_array_length (primes); i++)
439	sum += primes [i];	1218	sum += primes [i];
440		1219
441	=back	1220	=back
442		1221
		1222	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
443		1223
		1224	These symbols need to be defined before including F<ecb.h> the first time.
		1225
		1226	=over
		1227
		1228	=item ECB_NO_THREADS
		1229
		1230	If F<ecb.h> is never used from multiple threads, then this symbol can
		1231	be defined, in which case memory fences (and similar constructs) are
		1232	completely removed, leading to more efficient code and fewer dependencies.
		1233
		1234	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1235
		1236	=item ECB_NO_SMP
		1237
		1238	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1239	multiple threads, but never concurrently (e.g. if the system the program
		1240	runs on has only a single CPU with a single core, no hyperthreading and so
		1241	on), then this symbol can be defined, leading to more efficient code and
		1242	fewer dependencies.
		1243
		1244	=item ECB_NO_LIBM
		1245
		1246	When defined to C<1>, do not export any functions that might introduce
		1247	dependencies on the math library (usually called F<-lm>) - these are
		1248	marked with [-UECB_NO_LIBM].
		1249
		1250	=back
		1251
		1252	=head1 UNDOCUMENTED FUNCTIONALITY
		1253
		1254	F<ecb.h> is full of undocumented functionality as well, some of which is
		1255	intended to be internal-use only, some of which we forgot to document, and
		1256	some of which we hide because we are not sure we will keep the interface
		1257	stable.
		1258
		1259	While you are welcome to rummage around and use whatever you find useful
		1260	(we can't stop you), keep in mind that we will change undocumented
		1261	functionality in incompatible ways without thinking twice, while we are
		1262	considerably more conservative with documented things.
		1263
		1264	=head1 AUTHORS
		1265
		1266	C<libecb> is designed and maintained by:
		1267
		1268	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1269	Marc Alexander Lehmann <schmorp@schmorp.de>
		1270
		1271

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Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.17 by root, Thu May 26 23:55:58 2011 UTC vs.
Revision 1.95 by root, Sun Aug 1 10:00:33 2021 UTC