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Revision 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs.
Revision 1.88 by root, Mon Jun 21 21:49:51 2021 UTC

…		…
10		10
11	Its homepage can be found here:	11	Its homepage can be found here:
12		12
13	http://software.schmorp.de/pkg/libecb	13	http://software.schmorp.de/pkg/libecb
14		14
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around many compiler built-ins,
16	with replacement functions for other compilers. In addition to this,	16	together with replacement functions for other compilers. In addition
17	it provides a number of other lowlevel C utilities, such as endianness	17	to this, it provides a number of other lowlevel C utilities, such as
18	detection, byte swapping or bit rotations.	18	endianness detection, byte swapping or bit rotations.
19		19
20	Or in other words, things that should be built-in into any standard C	20	Or in other words, things that should be built into any standard C
21	system, but aren't.	21	system, but aren't, implemented as efficient as possible with GCC (clang,
		22	msvc...), and still correct with other compilers.
22		23
23	More might come.	24	More might come.
24		25
25	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
26		27
…		…
53	only a generic name is used (C<expr>, C<cond>, C<value> and so on), then	54	only a generic name is used (C<expr>, C<cond>, C<value> and so on), then
54	the corresponding function relies on C to implement the correct types, and	55	the corresponding function relies on C to implement the correct types, and
55	is usually implemented as a macro. Specifically, a "bool" in this manual	56	is usually implemented as a macro. Specifically, a "bool" in this manual
56	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
57		58
		59	=head2 TYPES / TYPE SUPPORT
		60
		61	ecb.h makes sure that the following types are defined (in the expected way):
		62
		63	int8_t uint8_
		64	int16_t uint16_t
		65	int32_t uint32_
		66	int64_t uint64_t
		67	int_fast8_t uint_fast8_t
		68	int_fast16_t uint_fast16_t
		69	int_fast32_t uint_fast32_t
		70	int_fast64_t uint_fast64_t
		71	intptr_t uintptr_t
		72
		73	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
		74	platform (currently C<4> or C<8>) and can be used in preprocessor
		75	expressions.
		76
		77	For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>.
		78
		79	=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
		80
		81	All the following symbols expand to an expression that can be tested in
		82	preprocessor instructions as well as treated as a boolean (use C<!!> to
		83	ensure it's either C<0> or C<1> if you need that).
		84
		85	=over
		86
		87	=item ECB_C
		88
		89	True if the implementation defines the C<__STDC__> macro to a true value,
		90	while not claiming to be C++, i..e C, but not C++.
		91
		92	=item ECB_C99
		93
		94	True if the implementation claims to be compliant to C99 (ISO/IEC
		95	9899:1999) or any later version, while not claiming to be C++.
		96
		97	Note that later versions (ECB_C11) remove core features again (for
		98	example, variable length arrays).
		99
		100	=item ECB_C11, ECB_C17
		101
		102	True if the implementation claims to be compliant to C11/C17 (ISO/IEC
		103	9899:2011, :20187) or any later version, while not claiming to be C++.
		104
		105	=item ECB_CPP
		106
		107	True if the implementation defines the C<__cplusplus__> macro to a true
		108	value, which is typically true for C++ compilers.
		109
		110	=item ECB_CPP11, ECB_CPP14, ECB_CPP17
		111
		112	True if the implementation claims to be compliant to C++11/C++14/C++17
		113	(ISO/IEC 14882:2011, :2014, :2017) or any later version.
		114
		115	Note that many C++20 features will likely have their own feature test
		116	macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>).
		117
		118	=item ECB_OPTIMIZE_SIZE
		119
		120	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
		121	can also be defined before including F<ecb.h>, in which case it will be
		122	unchanged.
		123
		124	=item ECB_GCC_VERSION (major, minor)
		125
		126	Expands to a true value (suitable for testing by the preprocessor) if the
		127	compiler used is GNU C and the version is the given version, or higher.
		128
		129	This macro tries to return false on compilers that claim to be GCC
		130	compatible but aren't.
		131
		132	=item ECB_EXTERN_C
		133
		134	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		135
		136	This can be used to declare a single external C function:
		137
		138	ECB_EXTERN_C int printf (const char *format, ...);
		139
		140	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		141
		142	These two macros can be used to wrap multiple C<extern "C"> definitions -
		143	they expand to nothing in C.
		144
		145	They are most useful in header files:
		146
		147	ECB_EXTERN_C_BEG
		148
		149	int mycfun1 (int x);
		150	int mycfun2 (int x);
		151
		152	ECB_EXTERN_C_END
		153
		154	=item ECB_STDFP
		155
		156	If this evaluates to a true value (suitable for testing by the
		157	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		158	and double/binary64 representations internally I<and> the endianness of
		159	both types match the endianness of C<uint32_t> and C<uint64_t>.
		160
		161	This means you can just copy the bits of a C<float> (or C<double>) to an
		162	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		163	without having to think about format or endianness.
		164
		165	This is true for basically all modern platforms, although F<ecb.h> might
		166	not be able to deduce this correctly everywhere and might err on the safe
		167	side.
		168
		169	=item ECB_64BIT_NATIVE
		170
		171	Evaluates to a true value (suitable for both preprocessor and C code
		172	testing) if 64 bit integer types on this architecture are evaluated
		173	"natively", that is, with similar speeds as 32 bit integerss. While 64 bit
		174	integer support is very common (and in fatc 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	A major part of libecb deals with GCC attributes. These are additional	234	A major part of libecb deals with additional attributes that can be
61	attributes that you cna assign to functions, variables and sometimes even	235	assigned to functions, variables and sometimes even types - much like
62	types - much like C<const> or C<volatile> in C.	236	C<const> or C<volatile> in C. They are implemented using either GCC
63		237	attributes or other compiler/language specific features. Attributes
64	While GCC allows declarations to show up in many surprising places,
65	but not in many expeted places, the safest way is to put attribute
66	declarations before the whole declaration:	238	declarations must be put before the whole declaration:
67		239
68	ecb_const int mysqrt (int a);	240	ecb_const int mysqrt (int a);
69	ecb_unused int i;	241	ecb_unused int i;
70		242
71	For variables, it is often nicer to put the attribute after the name, and
72	avoid multiple declarations using commas:
73
74	int i ecb_unused;
75
76	=over 4	243	=over
77
78	=item ecb_attribute ((attrs...))
79
80	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
81	nothing on other compilers, so the effect is that only GCC sees these.
82
83	Example: use the C<deprecated> attribute on a function.
84
85	ecb_attribute((__deprecated__)) void
86	do_not_use_me_anymore (void);
87		244
88	=item ecb_unused	245	=item ecb_unused
89		246
90	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
91	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
92	declare a variable but do not always use it:	249	you e.g. declare a variable but do not always use it:
93		250
94	{	251	{
95	int var ecb_unused;	252	ecb_unused int var;
96		253
97	#ifdef SOMECONDITION	254	#ifdef SOMECONDITION
98	var = ...;	255	var = ...;
99	return var;	256	return var;
100	#else	257	#else
101	return 0;	258	return 0;
102	#endif	259	#endif
103	}	260	}
104		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
105	=item ecb_noinline	287	=item ecb_noinline
106		288
107	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
108	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
109	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.
110		292
111	=item ecb_noreturn	293	=item ecb_noreturn
112		294
…		…
122	}	304	}
123		305
124	In this case, the compiler would probably be smart enough to deduce it on	306	In this case, the compiler would probably be smart enough to deduce it on
125	its own, so this is mainly useful for declarations.	307	its own, so this is mainly useful for declarations.
126		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	}
		329
127	=item ecb_const	330	=item ecb_const
128		331
129	Declares that the function only depends on the values of its arguments,	332	Declares that the function only depends on the values of its arguments,
130	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
131	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
…		…
183		386
184	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
185	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
186	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
187	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
188	C<ecb_unlikely> had been used to reach them.	391	C<ecb_expect_false> had been used to reach them.
189		392
190	Good examples for such functions would be error reporting functions, or	393	Good examples for such functions would be error reporting functions, or
191	functions only called in exceptional or rare cases.	394	functions only called in exceptional or rare cases.
192		395
193	=item ecb_artificial	396	=item ecb_artificial
194		397
195	Declares the function as "artificial", in this case meaning that this	398	Declares the function as "artificial", in this case meaning that this
196	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
197	- 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
198	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
199	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.
200		403
201	Marking them as artificial will instruct the debugger about just this,	404	Marking them as artificial will instruct the debugger about just this,
…		…
219		422
220	=back	423	=back
221		424
222	=head2 OPTIMISATION HINTS	425	=head2 OPTIMISATION HINTS
223		426
224	=over 4	427	=over
225		428
226	=item bool ecb_is_constant(expr)	429	=item bool ecb_is_constant (expr)
227		430
228	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
229	constant, and false otherwise.	432	constant, and false otherwise.
230		433
231	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
…		…
249	return is_constant (n) && !(n & (n - 1))	452	return is_constant (n) && !(n & (n - 1))
250	? rndm16 () & (num - 1)	453	? rndm16 () & (num - 1)
251	: (n * (uint32_t)rndm16 ()) >> 16;	454	: (n * (uint32_t)rndm16 ()) >> 16;
252	}	455	}
253		456
254	=item bool ecb_expect (expr, value)	457	=item ecb_expect (expr, value)
255		458
256	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
257	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
258	branch optimisations.	461	branch optimisations.
259		462
260	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
261	C<ecb_unlikely> functions instead.	464	C<ecb_expect_false> functions instead.
262		465
		466	=item bool ecb_expect_true (cond)
		467
263	=item bool ecb_likely (cond)	468	=item bool ecb_expect_false (cond)
264
265	=item bool ecb_unlikely (cond)
266		469
267	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
268	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
269	other conditional statement, it will not change the program:	472	other conditional statement, it will not change the program:
270		473
271	/* these two do the same thing */	474	/* these two do the same thing */
272	if (some_condition) ...;	475	if (some_condition) ...;
273	if (ecb_likely (some_condition)) ...;	476	if (ecb_expect_true (some_condition)) ...;
274		477
275	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
276	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
277	true).	480	unlikely to be true).
278		481
279	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
280	rare, exceptional, case, then use C<ecb_unlikely>:	483	rare, exceptional, case, then use C<ecb_expect_false>:
281		484
282	void my_free (void *ptr)	485	void my_free (void *ptr)
283	{	486	{
284	if (ecb_unlikely (ptr == 0))	487	if (ecb_expect_false (ptr == 0))
285	return;	488	return;
286	}	489	}
287		490
288	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
289	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
290	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.
291		500
292	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
293	memory block (for example, inside an implementation of a string stream) -	502	memory block (for example, inside an implementation of a string stream) -
294	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
295	you expect that most checks will turn out to be false:	504	you expect that most checks will turn out to be false:
296		505
297	/* make sure we have "size" extra room in our buffer */	506	/* make sure we have "size" extra room in our buffer */
298	ecb_inline void	507	ecb_inline void
299	reserve (int size)	508	reserve (int size)
300	{	509	{
301	if (ecb_unlikely (current + size > end))	510	if (ecb_expect_false (current + size > end))
302	real_reserve_method (size); /* presumably noinline */	511	real_reserve_method (size); /* presumably noinline */
303	}	512	}
304		513
305	=item bool ecb_assume (cond)	514	=item ecb_assume (cond)
306		515
307	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
308	obvious.	517	obvious. This is not a function, but a statement: it cannot be used in
		518	another expression.
309		519
310	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
311	conditions that might improve code generation, but which are impossible to	521	conditions that might improve code generation, but which are impossible to
312	deduce form the code itself.	522	deduce form the code itself.
313		523
314	For example, the example reservation function from the C<ecb_unlikely>	524	For example, the example reservation function from the C<ecb_expect_false>
315	description could be written thus (only C<ecb_assume> was added):	525	description could be written thus (only C<ecb_assume> was added):
316		526
317	ecb_inline void	527	ecb_inline void
318	reserve (int size)	528	reserve (int size)
319	{	529	{
320	if (ecb_unlikely (current + size > end))	530	if (ecb_expect_false (current + size > end))
321	real_reserve_method (size); /* presumably noinline */	531	real_reserve_method (size); /* presumably noinline */
322		532
323	ecb_assume (current + size <= end);	533	ecb_assume (current + size <= end);
324	}	534	}
325		535
…		…
330		540
331	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
332	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
333	call will never be executed.	543	call will never be executed.
334		544
335	=item bool ecb_unreachable ()	545	=item ecb_unreachable ()
336		546
337	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
338	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
339	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.
340		550
341	=item bool ecb_prefetch (addr, rw, locality)	551	=item ecb_prefetch (addr, rw, locality)
342		552
343	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
344	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
345	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
346	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
347	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
348	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>
349	and C<locality> must be compile-time constants.	559	and C<locality> must be compile-time constants.
350		560
		561	This is a statement, not a function: you cannot use it as part of an
		562	expression.
		563
351	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
352	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,
353	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.
354		567
355	int sum = 0;	568	int sum = 0;
…		…
374	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
375	cache.	588	cache.
376		589
377	=back	590	=back
378		591
379	=head2 BIT FIDDLING / BITSTUFFS	592	=head2 BIT FIDDLING / BIT WIZARDRY
380		593
381	=over 4	594	=over
382		595
383	=item bool ecb_big_endian ()	596	=item bool ecb_big_endian ()
384		597
385	=item bool ecb_little_endian ()	598	=item bool ecb_little_endian ()
386		599
387	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
388	(most-significant byte first) or little endian (least-significant byte	601	(most-significant byte first) or little endian (least-significant byte
389	first) respectively.	602	first) respectively.
390		603
		604	On systems that are neither, their return values are unspecified.
		605
391	=item int ecb_ctz32 (uint32_t x)	606	=item int ecb_ctz32 (uint32_t x)
392		607
		608	=item int ecb_ctz64 (uint64_t x)
		609
		610	=item int ecb_ctz (T x) [C++]
		611
393	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
394	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
395	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.
396	common use case is to compute the integer binary logarithm, i.e.,	615
397	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:
398		622
399	ecb_ctz32 (3) = 0	623	ecb_ctz32 (3) = 0
400	ecb_ctz32 (6) = 1	624	ecb_ctz32 (6) = 1
401		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
402	=item int ecb_popcount32 (uint32_t x)	661	=item int ecb_popcount32 (uint32_t x)
403		662
		663	=item int ecb_popcount64 (uint64_t x)
		664
		665	=item int ecb_popcount (T x) [C++]
		666
404	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:
405		675
406	ecb_popcount32 (7) = 3	676	ecb_popcount32 (7) = 3
407	ecb_popcount32 (255) = 8	677	ecb_popcount32 (255) = 8
408		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
409	=item uint32_t ecb_bswap16 (uint32_t x)	703	=item uint32_t ecb_bswap16 (uint32_t x)
410		704
411	=item uint32_t ecb_bswap32 (uint32_t x)	705	=item uint32_t ecb_bswap32 (uint32_t x)
412		706
		707	=item uint64_t ecb_bswap64 (uint64_t x)
		708
		709	=item T ecb_bswap (T x)
		710
413	These two functions return the value of the 16-bit (32-bit) value C<x>	711	These functions return the value of the 16-bit (32-bit, 64-bit) value
414	after reversing the order of bytes (0x11223344 becomes 0x44332211).	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)
415		729
416	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	730	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
417		731
418	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	732	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
419		733
420	These two functions return the value of C<x> after rotating all the bits	734	These two families of functions return the value of C<x> after rotating
421	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>).
422		737
423	Current GCC versions understand these functions and usually compile them	738	Current GCC/clang versions understand these functions and usually compile
424	to "optimal" code (e.g. a single C<roll> on x86).	739	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
		740	on x86).
		741
		742	=item T ecb_rotl (T x, unsigned int count) [C++]
		743
		744	=item T ecb_rotr (T x, unsigned int count) [C++]
		745
		746	Overloaded C++ rotl/rotr functions.
		747
		748	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		749
		750	=back
		751
		752	=head2 HOST ENDIANNESS CONVERSION
		753
		754	=over
		755
		756	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		757
		758	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		759
		760	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		761
		762	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		763
		764	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		765
		766	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		767
		768	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		769
		770	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		771	where C<be> and C<le> stand for big endian and little endian, respectively.
		772
		773	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		774
		775	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		776
		777	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		778
		779	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		780
		781	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		782
		783	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		784
		785	Like above, but converts I<from> host byte order to the specified
		786	endianness.
		787
		788	=back
		789
		790	In C++ the following additional template functions are supported:
		791
		792	=over
		793
		794	=item T ecb_be_to_host (T v)
		795
		796	=item T ecb_le_to_host (T v)
		797
		798	=item T ecb_host_to_be (T v)
		799
		800	=item T ecb_host_to_le (T v)
		801
		802	=back
		803
		804	These functions work like their C counterparts, above, but use templates,
		805	which make them useful in generic code.
		806
		807	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		808	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		809	again can be useful in generic code).
		810
		811	=head2 UNALIGNED LOAD/STORE
		812
		813	These function load or store unaligned multi-byte values.
		814
		815	=over
		816
		817	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		818
		819	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		820
		821	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		822
		823	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		824	memory.
		825
		826	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		827
		828	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		829
		830	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		831
		832	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		833
		834	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		835
		836	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		837
		838	Like above, but additionally convert from big endian (C<be>) or little
		839	endian (C<le>) byte order to host byte order while doing so.
		840
		841	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		842
		843	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		844
		845	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		846
		847	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		848	memory.
		849
		850	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		851
		852	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		853
		854	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		855
		856	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		857
		858	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		859
		860	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		861
		862	Like above, but additionally convert from host byte order to big endian
		863	(C<be>) or little endian (C<le>) byte order while doing so.
		864
		865	=back
		866
		867	In C++ the following additional template functions are supported:
		868
		869	=over
		870
		871	=item T ecb_peek<T> (const void *ptr)
		872
		873	=item T ecb_peek_be<T> (const void *ptr)
		874
		875	=item T ecb_peek_le<T> (const void *ptr)
		876
		877	=item T ecb_peek_u<T> (const void *ptr)
		878
		879	=item T ecb_peek_be_u<T> (const void *ptr)
		880
		881	=item T ecb_peek_le_u<T> (const void *ptr)
		882
		883	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		884	32 or 64 bit value from memory, with optional conversion from big/little
		885	endian.
		886
		887	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		888
		889	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		890
		891	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		892
		893	Unlike their C counterparts, these functions support 8 bit quantities
		894	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		895	all of which hopefully makes them more useful in generic code.
		896
		897	=item ecb_poke (void *ptr, T v)
		898
		899	=item ecb_poke_be (void *ptr, T v)
		900
		901	=item ecb_poke_le (void *ptr, T v)
		902
		903	=item ecb_poke_u (void *ptr, T v)
		904
		905	=item ecb_poke_be_u (void *ptr, T v)
		906
		907	=item ecb_poke_le_u (void *ptr, T v)
		908
		909	Again, similarly to their C counterparts, these functions store an
		910	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		911	big/little endian.
		912
		913	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		914
		915	Unlike their C counterparts, these functions support 8 bit quantities
		916	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		917	all of which hopefully makes them more useful in generic code.
		918
		919	=back
		920
		921	=head2 FLOATING POINT FIDDLING
		922
		923	=over
		924
		925	=item ECB_INFINITY [-UECB_NO_LIBM]
		926
		927	Evaluates to positive infinity if supported by the platform, otherwise to
		928	a truly huge number.
		929
		930	=item ECB_NAN [-UECB_NO_LIBM]
		931
		932	Evaluates to a quiet NAN if supported by the platform, otherwise to
		933	C<ECB_INFINITY>.
		934
		935	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		936
		937	Same as C<ldexpf>, but always available.
		938
		939	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		940
		941	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		942
		943	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		944
		945	These functions each take an argument in the native C<float> or C<double>
		946	type and return the IEEE 754 bit representation of it (binary16/half,
		947	binary32/single or binary64/double precision).
		948
		949	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		950	will be the most significant bit, followed by exponent and mantissa.
		951
		952	This function should work even when the native floating point format isn't
		953	IEEE compliant, of course at a speed and code size penalty, and of course
		954	also within reasonable limits (it tries to convert NaNs, infinities and
		955	denormals, but will likely convert negative zero to positive zero).
		956
		957	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		958	be able to optimise away this function completely.
		959
		960	These functions can be helpful when serialising floats to the network - you
		961	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		962
		963	Another use for these functions is to manipulate floating point values
		964	directly.
		965
		966	Silly example: toggle the sign bit of a float.
		967
		968	/* On gcc-4.7 on amd64, */
		969	/* this results in a single add instruction to toggle the bit, and 4 extra */
		970	/* instructions to move the float value to an integer register and back. */
		971
		972	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		973
		974	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		975
		976	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		977
		978	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		979
		980	The reverse operation of the previous function - takes the bit
		981	representation of an IEEE binary16, binary32 or binary64 number (half,
		982	single or double precision) and converts it to the native C<float> or
		983	C<double> format.
		984
		985	This function should work even when the native floating point format isn't
		986	IEEE compliant, of course at a speed and code size penalty, and of course
		987	also within reasonable limits (it tries to convert normals and denormals,
		988	and might be lucky for infinities, and with extraordinary luck, also for
		989	negative zero).
		990
		991	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		992	be able to optimise away this function completely.
		993
		994	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		995
		996	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		997
		998	Convert a IEEE binary32/single precision to binary16/half format, and vice
		999	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1000	and NaNs) correctly.
		1001
		1002	These are functions are available under C<-DECB_NO_LIBM>, since
		1003	they do not rely on the platform floating point format. The
		1004	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1005	usually what you want.
425		1006
426	=back	1007	=back
427		1008
428	=head2 ARITHMETIC	1009	=head2 ARITHMETIC
429		1010
430	=over 4	1011	=over
431		1012
432	=item x = ecb_mod (m, n)	1013	=item x = ecb_mod (m, n)
433		1014
434	Returns the positive remainder of the modulo operation between C<m> and	1015	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1016	of the division operation between C<m> and C<n>, using floored
435	C<n>. Unlike the C modulo operator C<%>, this function ensures that the	1017	division. Unlike the C remainder operator C<%>, this function ensures that
436	return value is always positive - ISO C guarantees very little when	1018	the return value is always positive and that the two numbers I<m> and
437	negative numbers are used with C<%>.	1019	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1020	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1021	in the language.
438		1022
439	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be	1023	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
440	negatable, that is, both C<m> and C<-m> must be representable in its	1024	negatable, that is, both C<m> and C<-m> must be representable in its
441	type.	1025	type (this typically excludes the minimum signed integer value, the same
		1026	limitation as for C</> and C<%> in C).
		1027
		1028	Current GCC/clang versions compile this into an efficient branchless
		1029	sequence on almost all CPUs.
		1030
		1031	For example, when you want to rotate forward through the members of an
		1032	array for increasing C<m> (which might be negative), then you should use
		1033	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1034	change direction for negative values:
		1035
		1036	for (m = -100; m <= 100; ++m)
		1037	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1038
		1039	=item x = ecb_div_rd (val, div)
		1040
		1041	=item x = ecb_div_ru (val, div)
		1042
		1043	Returns C<val> divided by C<div> rounded down or up, respectively.
		1044	C<val> and C<div> must have integer types and C<div> must be strictly
		1045	positive. Note that these functions are implemented with macros in C
		1046	and with function templates in C++.
442		1047
443	=back	1048	=back
444		1049
445	=head2 UTILITY	1050	=head2 UTILITY
446		1051
447	=over 4	1052	=over
448		1053
449	=item element_count = ecb_array_length (name)	1054	=item element_count = ecb_array_length (name)
450		1055
451	Returns the number of elements in the array C<name>. For example:	1056	Returns the number of elements in the array C<name>. For example:
452		1057
…		…
456	for (i = 0; i < ecb_array_length (primes); i++)	1061	for (i = 0; i < ecb_array_length (primes); i++)
457	sum += primes [i];	1062	sum += primes [i];
458		1063
459	=back	1064	=back
460		1065
		1066	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
461		1067
		1068	These symbols need to be defined before including F<ecb.h> the first time.
		1069
		1070	=over
		1071
		1072	=item ECB_NO_THREADS
		1073
		1074	If F<ecb.h> is never used from multiple threads, then this symbol can
		1075	be defined, in which case memory fences (and similar constructs) are
		1076	completely removed, leading to more efficient code and fewer dependencies.
		1077
		1078	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1079
		1080	=item ECB_NO_SMP
		1081
		1082	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1083	multiple threads, but never concurrently (e.g. if the system the program
		1084	runs on has only a single CPU with a single core, no hyperthreading and so
		1085	on), then this symbol can be defined, leading to more efficient code and
		1086	fewer dependencies.
		1087
		1088	=item ECB_NO_LIBM
		1089
		1090	When defined to C<1>, do not export any functions that might introduce
		1091	dependencies on the math library (usually called F<-lm>) - these are
		1092	marked with [-UECB_NO_LIBM].
		1093
		1094	=back
		1095
		1096	=head1 UNDOCUMENTED FUNCTIONALITY
		1097
		1098	F<ecb.h> is full of undocumented functionality as well, some of which is
		1099	intended to be internal-use only, some of which we forgot to document, and
		1100	some of which we hide because we are not sure we will keep the interface
		1101	stable.
		1102
		1103	While you are welcome to rummage around and use whatever you find useful
		1104	(we can't stop you), keep in mind that we will change undocumented
		1105	functionality in incompatible ways without thinking twice, while we are
		1106	considerably more conservative with documented things.
		1107
		1108	=head1 AUTHORS
		1109
		1110	C<libecb> is designed and maintained by:
		1111
		1112	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1113	Marc Alexander Lehmann <schmorp@schmorp.de>
		1114
		1115

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Comparing libecb/ecb.pod (file contents): Revision 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs. Revision 1.88 by root, Mon Jun 21 21:49:51 2021 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs.
Revision 1.88 by root, Mon Jun 21 21:49:51 2021 UTC