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		1	=head1 LIBECB - e-C-Builtins
		2
1	=head1 LIBECB	3	=head2 ABOUT LIBECB
2		4
3	You suck, we don't(tm)	5	Libecb is currently a simple header file that doesn't require any
		6	configuration to use or include in your project.
		7
		8	It's part of the e-suite of libraries, other members of which include
		9	libev and libeio.
		10
		11	Its homepage can be found here:
		12
		13	http://software.schmorp.de/pkg/libecb
		14
		15	It mainly provides a number of wrappers around many compiler built-ins,
		16	together with replacement functions for other compilers. In addition
		17	to this, it provides a number of other low-level C utilities, such as
		18	endianness detection, byte swapping or bit rotations.
		19
		20	Or in other words, things that should be built into any standard C
		21	system, but aren't, implemented as efficient as possible with GCC (clang,
		22	MSVC...), and still correct with other compilers.
		23
		24	More might come.
4		25
5	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
6		27
7	- how to include it	28	At the moment, all you have to do is copy F<ecb.h> somewhere where your
8	- it includes inttypes.h	29	compiler can find it and include it:
9	- no .a
10	- whats a bool
11		30
		31	#include <ecb.h>
		32
		33	The header should work fine for both C and C++ compilation, and gives you
		34	all of F<inttypes.h> in addition to the ECB symbols.
		35
		36	There are currently no object files to link to - future versions might
		37	come with an (optional) object code library to link against, to reduce
		38	code size or gain access to additional features.
		39
		40	It also currently includes everything from F<inttypes.h>.
		41
		42	=head2 ABOUT THIS MANUAL / CONVENTIONS
		43
		44	This manual mainly describes each (public) function available after
		45	including the F<ecb.h> header. The header might define other symbols than
		46	these, but these are not part of the public API, and not supported in any
		47	way.
		48
		49	When the manual mentions a "function" then this could be defined either as
		50	as inline function, a macro, or an external symbol.
		51
		52	When functions use a concrete standard type, such as C<int> or
		53	C<uint32_t>, then the corresponding function works only with that type. If
		54	only a generic name is used (C<expr>, C<cond>, C<value> and so on), then
		55	the corresponding function relies on C to implement the correct types, and
		56	is usually implemented as a macro. Specifically, a "bool" in this manual
		57	refers to any kind of boolean value, not a specific type.
		58
		59	=head2 TYPES / TYPE SUPPORT
		60
		61	F<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
12	=head2 GCC ATTRIBUTES	232	=head2 ATTRIBUTES
13		233
14	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:
15		239
		240	ecb_const int mysqrt (int a);
		241	ecb_unused int i;
		242
16	=over 4	243	=over
17
18	=item ecb_attribute ((attrs...))
19
20	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and
21	to nothing on other compilers, so the effect is that only GCC sees these.
22		244
23	=item ecb_unused	245	=item ecb_unused
24		246
25	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
26	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
27	declare a variable but do not always use it:	249	you e.g. declare a variable but do not always use it:
28		250
		251	{
		252	ecb_unused int var;
		253
		254	#ifdef SOMECONDITION
		255	var = ...;
		256	return var;
		257	#else
		258	return 0;
		259	#endif
		260	}
		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 code size.
		280
		281	ecb_inline int
		282	negmul (int a, int b)
29	{	283	{
30	int var ecb_unused;	284	return - (a * b);
31
32	#ifdef SOMECONDITION
33	var = ...;
34	return var;
35	#else
36	return 0;
37	#endif
38	}	285	}
39		286
40	=item ecb_noinline	287	=item ecb_noinline
41		288
42	Prevent a function from being inlined - it might be optimsied away, but	289	Prevents a function from being inlined - it might be optimised away, but
43	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
44	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.
45		292
46	=item ecb_noreturn	293	=item ecb_noreturn
47		294
		295	Marks a function as "not returning, ever". Some typical functions that
		296	don't return are C<exit> or C<abort> (which really works hard to not
		297	return), and now you can make your own:
		298
		299	ecb_noreturn void
		300	my_abort (const char *errline)
		301	{
		302	puts (errline);
		303	abort ();
		304	}
		305
		306	In this case, the compiler would probably be smart enough to deduce it on
		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	}
		329
48	=item ecb_const	330	=item ecb_const
49		331
		332	Declares that the function only depends on the values of its arguments,
		333	much like a mathematical function. It specifically does not read or write
		334	any memory any arguments might point to, global variables, or call any
		335	non-const functions. It also must not have any side effects.
		336
		337	Such a function can be optimised much more aggressively by the compiler -
		338	for example, multiple calls with the same arguments can be optimised into
		339	a single call, which wouldn't be possible if the compiler would have to
		340	expect any side effects.
		341
		342	It is best suited for functions in the sense of mathematical functions,
		343	such as a function returning the square root of its input argument.
		344
		345	Not suited would be a function that calculates the hash of some memory
		346	area you pass in, prints some messages or looks at a global variable to
		347	decide on rounding.
		348
		349	See C<ecb_pure> for a slightly less restrictive class of functions.
		350
50	=item ecb_pure	351	=item ecb_pure
51		352
		353	Similar to C<ecb_const>, declares a function that has no side
		354	effects. Unlike C<ecb_const>, the function is allowed to examine global
		355	variables and any other memory areas (such as the ones passed to it via
		356	pointers).
		357
		358	While these functions cannot be optimised as aggressively as C<ecb_const>
		359	functions, they can still be optimised away in many occasions, and the
		360	compiler has more freedom in moving calls to them around.
		361
		362	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		363	function that calculates the MD5 sum of some input and updates some MD5
		364	state passed as argument would I<NOT> be pure, however, as it would modify
		365	some memory area that is not the return value.
		366
52	=item ecb_hot	367	=item ecb_hot
53		368
		369	This declares a function as "hot" with regards to the cache - the function
		370	is used so often, that it is very beneficial to keep it in the cache if
		371	possible.
		372
		373	The compiler reacts by trying to place hot functions near to each other in
		374	memory.
		375
		376	Whether a function is hot or not often depends on the whole program,
		377	and less on the function itself. C<ecb_cold> is likely more useful in
		378	practise.
		379
54	=item ecb_cold	380	=item ecb_cold
55		381
		382	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		383	the cache, or in other words, this function is not called often, or not at
		384	speed-critical times, and keeping it in the cache might be a waste of said
		385	cache.
		386
		387	In addition to placing cold functions together (or at least away from hot
		388	functions), this knowledge can be used in other ways, for example, the
		389	function will be optimised for size, as opposed to speed, and code paths
		390	leading to calls to those functions can automatically be marked as if
		391	C<ecb_expect_false> had been used to reach them.
		392
		393	Good examples for such functions would be error reporting functions, or
		394	functions only called in exceptional or rare cases.
		395
56	=item ecb_artificial	396	=item ecb_artificial
57		397
		398	Declares the function as "artificial", in this case meaning that this
		399	function is not really meant to be a function, but more like an accessor
		400	- many methods in C++ classes are mere accessor functions, and having a
		401	crash reported in such a method, or single-stepping through them, is not
		402	usually so helpful, especially when it's inlined to just a few instructions.
		403
		404	Marking them as artificial will instruct the debugger about just this,
		405	leading to happier debugging and thus happier lives.
		406
		407	Example: in some kind of smart-pointer class, mark the pointer accessor as
		408	artificial, so that the whole class acts more like a pointer and less like
		409	some C++ abstraction monster.
		410
		411	template<typename T>
		412	struct my_smart_ptr
		413	{
		414	T *value;
		415
		416	ecb_artificial
		417	operator T *()
		418	{
		419	return value;
		420	}
		421	};
		422
58	=back	423	=back
59		424
60	=head2 OPTIMISATION HINTS	425	=head2 OPTIMISATION HINTS
61		426
62	=over 4	427	=over
63		428
64	=item bool ecb_is_constant(expr)	429	=item bool ecb_is_constant (expr)
65		430
66	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
67	constant, and false otherwise.	432	constant, and false otherwise.
68		433
69	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
70	random number, and you have a function that maps this to a range from	435	random number, and you have a function that maps this to a range from
71	0..n-1, then you could use this inline fucntion in a header file:	436	0..n-1, then you could use this inline function in a header file:
72		437
73	ecb_inline uint32_t	438	ecb_inline uint32_t
74	rndm (uint32_t n)	439	rndm (uint32_t n)
75	{	440	{
76	return n * (uint32_t)rndm16 ()) >> 16;	441	return (n * (uint32_t)rndm16 ()) >> 16;
77	}	442	}
78		443
79	However, for powers of two, you could use a normal mask, but that is only	444	However, for powers of two, you could use a normal mask, but that is only
80	worth it if, at compile time, you can detect this case. This is the case	445	worth it if, at compile time, you can detect this case. This is the case
81	when the passed number is a constant and also a power of two (C<n & (n -	446	when the passed number is a constant and also a power of two (C<n & (n -
…		…
84	ecb_inline uint32_t	449	ecb_inline uint32_t
85	rndm (uint32_t n)	450	rndm (uint32_t n)
86	{	451	{
87	return is_constant (n) && !(n & (n - 1))	452	return is_constant (n) && !(n & (n - 1))
88	? rndm16 () & (num - 1)	453	? rndm16 () & (num - 1)
89	: (uint32_t)rndm16 ()) >> 16;	454	: (n * (uint32_t)rndm16 ()) >> 16;
90	}	455	}
91		456
92
93
94	=item bool ecb_expect(expr,value)	457	=item ecb_expect (expr, value)
95		458
96	=item bool ecb_unlikely(bool)	459	Evaluates C<expr> and returns it. In addition, it tells the compiler that
		460	the C<expr> evaluates to C<value> a lot, which can be used for static
		461	branch optimisations.
97		462
98	=item bool ecb_likely(bool)	463	Usually, you want to use the more intuitive C<ecb_expect_true> and
		464	C<ecb_expect_false> functions instead.
99		465
		466	=item bool ecb_expect_true (cond)
		467
		468	=item bool ecb_expect_false (cond)
		469
		470	These two functions expect a expression that is true or false and return
		471	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
		472	other conditional statement, it will not change the program:
		473
		474	/* these two do the same thing */
		475	if (some_condition) ...;
		476	if (ecb_expect_true (some_condition)) ...;
		477
		478	However, by using C<ecb_expect_true>, you tell the compiler that the
		479	condition is likely to be true (and for C<ecb_expect_false>, that it is
		480	unlikely to be true).
		481
		482	For example, when you check for a null pointer and expect this to be a
		483	rare, exceptional, case, then use C<ecb_expect_false>:
		484
		485	void my_free (void *ptr)
		486	{
		487	if (ecb_expect_false (ptr == 0))
		488	return;
		489	}
		490
		491	Consequent use of these functions to mark away exceptional cases or to
		492	tell the compiler what the hot path through a function is can increase
		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.
		500
		501	A very good example is in a function that reserves more space for some
		502	memory block (for example, inside an implementation of a string stream) -
		503	each time something is added, you have to check for a buffer overrun, but
		504	you expect that most checks will turn out to be false:
		505
		506	/* make sure we have "size" extra room in our buffer */
		507	ecb_inline void
		508	reserve (int size)
		509	{
		510	if (ecb_expect_false (current + size > end))
		511	real_reserve_method (size); /* presumably noinline */
		512	}
		513
100	=item bool ecb_assume(cond)	514	=item ecb_assume (cond)
101		515
		516	Tries to tell the compiler that some condition is true, even if it's not
		517	obvious. This is not a function, but a statement: it cannot be used in
		518	another expression.
		519
		520	This can be used to teach the compiler about invariants or other
		521	conditions that might improve code generation, but which are impossible to
		522	deduce form the code itself.
		523
		524	For example, the example reservation function from the C<ecb_expect_false>
		525	description could be written thus (only C<ecb_assume> was added):
		526
		527	ecb_inline void
		528	reserve (int size)
		529	{
		530	if (ecb_expect_false (current + size > end))
		531	real_reserve_method (size); /* presumably noinline */
		532
		533	ecb_assume (current + size <= end);
		534	}
		535
		536	If you then call this function twice, like this:
		537
		538	reserve (10);
		539	reserve (1);
		540
		541	Then the compiler I<might> be able to optimise out the second call
		542	completely, as it knows that C<< current + 1 > end >> is false and the
		543	call will never be executed.
		544
102	=item bool ecb_unreachable()	545	=item ecb_unreachable ()
103		546
		547	This function does nothing itself, except tell the compiler that it will
		548	never be executed. Apart from suppressing a warning in some cases, this
		549	function can be used to implement C<ecb_assume> or similar functionality.
		550
104	=item bool ecb_prefetch(addr,rw,locality)	551	=item ecb_prefetch (addr, rw, locality)
105		552
106	=back	553	Tells the compiler to try to prefetch memory at the given I<addr>ess
		554	for either reading (I<rw> = 0) or writing (I<rw> = 1). A I<locality> of
		555	C<0> means that there will only be one access later, C<3> means that
		556	the data will likely be accessed very often, and values in between mean
		557	something... in between. The memory pointed to by the address does not
		558	need to be accessible (it could be a null pointer for example), but C<rw>
		559	and C<locality> must be compile-time constants.
107		560
		561	This is a statement, not a function: you cannot use it as part of an
		562	expression.
		563
		564	An obvious way to use this is to prefetch some data far away, in a big
		565	array you loop over. This prefetches memory some 128 array elements later,
		566	in the hope that it will be ready when the CPU arrives at that location.
		567
		568	int sum = 0;
		569
		570	for (i = 0; i < N; ++i)
		571	{
		572	sum += arr [i]
		573	ecb_prefetch (arr + i + 128, 0, 0);
		574	}
		575
		576	It's hard to predict how far to prefetch, and most CPUs that can prefetch
		577	are often good enough to predict this kind of behaviour themselves. It
		578	gets more interesting with linked lists, especially when you do some fair
		579	processing on each list element:
		580
		581	for (node *n = start; n; n = n->next)
		582	{
		583	ecb_prefetch (n->next, 0, 0);
		584	... do medium amount of work with *n
		585	}
		586
		587	After processing the node, (part of) the next node might already be in
		588	cache.
		589
		590	=back
		591
108	=head2 BIT FIDDLING / BITSTUFFS	592	=head2 BIT FIDDLING / BIT WIZARDRY
		593
		594	=over
109		595
110	=item bool ecb_big_endian ()	596	=item bool ecb_big_endian ()
111		597
112	=item bool ecb_little_endian ()	598	=item bool ecb_little_endian ()
113		599
		600	These two functions return true if the byte order is big endian
		601	(most-significant byte first) or little endian (least-significant byte
		602	first) respectively.
		603
		604	On systems that are neither, their return values are unspecified.
		605
114	=item int ecb_ctz32 (uint32_t x)	606	=item int ecb_ctz32 (uint32_t x)
115		607
		608	=item int ecb_ctz64 (uint64_t x)
		609
		610	=item int ecb_ctz (T x) [C++]
		611
		612	Returns the index of the least significant bit set in C<x> (or
		613	equivalently the number of bits set to 0 before the least significant bit
		614	set), starting from 0. If C<x> is 0 the result is undefined.
		615
		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:
		622
		623	ecb_ctz32 (3) = 0
		624	ecb_ctz32 (6) = 1
		625
		626	=item int ecb_clz32 (uint32_t x)
		627
		628	=item int ecb_clz64 (uint64_t x)
		629
		630	=item int ecb_clz (T x) [C++]
		631
		632	Counts the number of leading zero bits in C<x>. If C<x> is 0 the result is
		633	undefined.
		634
		635	The overloaded C++ C<ecb_clz> function supports C<uint32_t> and
		636	C<uint64_t> types only.
		637
		638	It is often simpler to use one of the C<ecb_ld*> functions instead, whoise
		639	result only depends on the value and not the size of the type.
		640
		641	For example:
		642
		643	ecb_clz32 (3) = 30
		644	ecb_clz32 (6) = 29
		645
		646	=item bool ecb_is_pot32 (uint32_t x)
		647
		648	=item bool ecb_is_pot64 (uint32_t x)
		649
		650	=item bool ecb_is_pot (T x) [C++]
		651
		652	Returns true iff C<x> is a power of two or C<x == 0>.
		653
		654	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		655
		656	The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
		657	C<uint32_t> and C<uint64_t> types.
		658
		659	=item int ecb_ld32 (uint32_t x)
		660
		661	=item int ecb_ld64 (uint64_t x)
		662
		663	=item int ecb_ld64 (T x) [C++]
		664
		665	Returns the index of the most significant bit set in C<x>, or the number
		666	of digits the number requires in binary (so that C<< 2**ld <= x <
		667	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		668	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		669	example to see how many bits a certain number requires to be encoded.
		670
		671	This function is similar to the "count leading zero bits" function, except
		672	that that one returns how many zero bits are "in front" of the number (in
		673	the given data type), while C<ecb_ld> returns how many bits the number
		674	itself requires.
		675
		676	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		677
		678	The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
		679	C<uint32_t> and C<uint64_t> types.
		680
116	=item int ecb_popcount32 (uint32_t x)	681	=item int ecb_popcount32 (uint32_t x)
117		682
		683	=item int ecb_popcount64 (uint64_t x)
		684
		685	=item int ecb_popcount (T x) [C++]
		686
		687	Returns the number of bits set to 1 in C<x>.
		688
		689	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		690
		691	The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
		692	C<uint32_t> and C<uint64_t> types.
		693
		694	For example:
		695
		696	ecb_popcount32 (7) = 3
		697	ecb_popcount32 (255) = 8
		698
		699	=item uint8_t ecb_bitrev8 (uint8_t x)
		700
		701	=item uint16_t ecb_bitrev16 (uint16_t x)
		702
		703	=item uint32_t ecb_bitrev32 (uint32_t x)
		704
		705	=item T ecb_bitrev (T x) [C++]
		706
		707	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		708	and so on.
		709
		710	The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
		711
		712	Example:
		713
		714	ecb_bitrev8 (0xa7) = 0xea
		715	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		716
		717	=item T ecb_bitrev (T x) [C++]
		718
		719	Overloaded C++ bitrev function.
		720
		721	C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
		722
		723	=item uint32_t ecb_bswap16 (uint32_t x)
		724
118	=item uint32_t ecb_bswap32 (uint32_t x)	725	=item uint32_t ecb_bswap32 (uint32_t x)
119		726
120	=item uint32_t ecb_bswap16 (uint32_t x)	727	=item uint64_t ecb_bswap64 (uint64_t x)
		728
		729	=item T ecb_bswap (T x)
		730
		731	These functions return the value of the 16-bit (32-bit, 64-bit) value
		732	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		733	C<ecb_bswap32>).
		734
		735	The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
		736	C<uint32_t> and C<uint64_t> types.
		737
		738	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		739
		740	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		741
		742	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		743
		744	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		745
		746	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		747
		748	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
121		749
122	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	750	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
123		751
124	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	752	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
		753
		754	These two families of functions return the value of C<x> after rotating
		755	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		756	(C<ecb_rotl>). There are no restrictions on the value C<count>, i.e. both
		757	zero and values equal or larger than the word width work correctly. Also,
		758	notwithstanding C<count> being unsigned, negative numbers work and shift
		759	to the opposite direction.
		760
		761	Current GCC/clang versions understand these functions and usually compile
		762	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
		763	on x86).
		764
		765	=item T ecb_rotl (T x, unsigned int count) [C++]
		766
		767	=item T ecb_rotr (T x, unsigned int count) [C++]
		768
		769	Overloaded C++ rotl/rotr functions.
		770
		771	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		772
		773	=item uint_fast8_t ecb_gray8_encode (uint_fast8_t b)
		774
		775	=item uint_fast16_t ecb_gray16_encode (uint_fast16_t b)
		776
		777	=item uint_fast32_t ecb_gray32_encode (uint_fast32_t b)
		778
		779	=item uint_fast64_t ecb_gray64_encode (uint_fast64_t b)
		780
		781	Encode an unsigned into its corresponding (reflective) gray code - the
		782	kind of gray code meant when just talking about "gray code". These
		783	functions are very fast and all have identical implementation, so there is
		784	no need to use a smaller type, as long as your CPU can handle it natively.
		785
		786	=item T ecb_gray_encode (T b) [C++]
		787
		788	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		789
		790	=item uint_fast8_t ecb_gray8_decode (uint_fast8_t b)
		791
		792	=item uint_fast16_t ecb_gray16_decode (uint_fast16_t b)
		793
		794	=item uint_fast32_t ecb_gray32_decode (uint_fast32_t b)
		795
		796	=item uint_fast64_t ecb_gray64_decode (uint_fast64_t b)
		797
		798	Decode a gray code back into linear index form (the reverse of
		799	C<ecb_gray*_encode>. Unlike the encode functions, the decode functions
		800	have higher time complexity for larger types, so it can pay off to use a
		801	smaller type here.
		802
		803	=item T ecb_gray_decode (T b) [C++]
		804
		805	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		806
		807	=back
		808
		809	=head2 HILBERT CURVES
		810
		811	These functions deal with (square, pseudo) Hilbert curves. The parameter
		812	I<order> indicates the size of the square and is specified in bits, that
		813	means for order C<8>, the coordinates range from C<0>..C<255>, and the
		814	curve index ranges from C<0>..C<65535>.
		815
		816	The 32 bit variants of these functions map a 32 bit index to two 16 bit
		817	coordinates, stored in a 32 bit variable, where the high order bits are
		818	the x-coordinate, and the low order bits are the y-coordinate, thus,
		819	these functions map 32 bit linear index on the curve to a 32 bit packed
		820	coordinate pair, and vice versa.
		821
		822	The 64 bit variants work similarly.
		823
		824	The I<order> can go from C<1> to C<16> for the 32 bit curve, and C<1> to
		825	C<32> for the 64 bit curve.
		826
		827	When going from one order to the next higher order, these functions
		828	replace the curve segments by smaller versions of the generating shape,
		829	while doubling the size (since they use integer coordinates), which is
		830	what you would expect mathematically. This means that the curve will be
		831	mirrored at the diagonal. If your goal is to simply cover more area while
		832	retaining existing point coordinates you should increase or decrease the
		833	I<order> by C<2> or, in the case of C<ecb_hilbert2d_index_to_coord>,
		834	simply specify the maximum I<order> of C<16> or C<32>, respectively, as
		835	these are constant-time.
		836
		837	=over
		838
		839	=item uint32_t ecb_hilbert2d_index_to_coord32 (int order, uint32_t index)
		840
		841	=item uint64_t ecb_hilbert2d_index_to_coord64 (int order, uint64_t index)
		842
		843	Map a point on a pseudo Hilbert curve from its linear distance from the
		844	origin on the curve to a x|y coordinate pair. The result is a packed
		845	coordinate pair, to get the actual x and < coordinates, you could do
		846	something like this:
		847
		848	uint32_t xy = ecb_hilbert2d_index_to_coord32 (16, 255);
		849	uint16_t x = xy >> 16;
		850	uint16_t y = xy & 0xffffU;
		851
		852	uint64_t xy = ecb_hilbert2d_index_to_coord64 (32, 255);
		853	uint32_t x = xy >> 32;
		854	uint32_t y = xy & 0xffffffffU;
		855
		856	These functions work in constant time, so for many applications it is
		857	preferable to simply hard-code the order to the maximum (C<16> or C<32>).
		858
		859	This (production-ready, i.e. never run) example generates an SVG image of
		860	an order 8 pseudo Hilbert curve:
		861
		862	printf ("<svg xmlns='http://www.w3.org/2000/svg' width='%d' height='%d'>\n", 64 * 8, 64 * 8);
		863	printf ("<g transform='translate(4) scale(8)' stroke-width='0.25' stroke='black'>\n");
		864	for (uint32_t i = 0; i < 64*64 - 1; ++i)
		865	{
		866	uint32_t p1 = ecb_hilbert2d_index_to_coord32 (6, i );
		867	uint32_t p2 = ecb_hilbert2d_index_to_coord32 (6, i + 1);
		868	printf ("<line x1='%d' y1='%d' x2='%d' y2='%d'/>\n",
		869	p1 >> 16, p1 & 0xffff,
		870	p2 >> 16, p2 & 0xffff);
		871	}
		872	printf ("</g>\n");
		873	printf ("</svg>\n");
		874
		875	=item uint32_t ecb_hilbert2d_coord_to_index32 (int order, uint32_t xy)
		876
		877	=item uint64_t ecb_hilbert2d_coord_to_index64 (int order, uint64_t xy)
		878
		879	The reverse of C<ecb_hilbert2d_index_to_coord> - map a packed pair of
		880	coordinates to their linear index on the pseudo Hilbert curve of order
		881	I<order>.
		882
		883	They are an exact inverse of the C<ecb_hilbert2d_coord_to_index> functions
		884	for the same I<order>:
		885
		886	assert (
		887	u == ecb_hilbert2d_coord_to_index (32,
		888	ecb_hilbert2d_index_to_coord32 (32,
		889	u)));
		890
		891	Packing coordinates is done the same way, as well, from I<x> and I<y>:
		892
		893	uint32_t xy = ((uint32_t)x << 16) | y; // for ecb_hilbert2d_coord_to_index32
		894	uint64_t xy = ((uint64_t)x << 32) | y; // for ecb_hilbert2d_coord_to_index64
		895
		896	Unlike C<ecb_hilbert2d_coord_to_index>, these functions are O(I<order>),
		897	so it is preferable to use the lowest possible order.
		898
		899	=back
		900
		901	=head2 BIT MIXING, HASHING
		902
		903	Sometimes you have an integer and want to distribute its bits well, for
		904	example, to use it as a hash in a hash table. A common example is pointer
		905	values, which often only have a limited range (e.g. low and high bits are
		906	often zero).
		907
		908	The following functions try to mix the bits to get a good bias-free
		909	distribution. They were mainly made for pointers, but the underlying
		910	integer functions are exposed as well.
		911
		912	As an added benefit, the functions are reversible, so if you find it
		913	convenient to store only the hash value, you can recover the original
		914	pointer from the hash ("unmix"), as long as your pointers are 32 or 64 bit
		915	(if this isn't the case on your platform, drop us a note and we will add
		916	functions for other bit widths).
		917
		918	The unmix functions are very slightly slower than the mix functions, so
		919	it is equally very slightly preferable to store the original values wehen
		920	convenient.
		921
		922	The underlying algorithm if subject to change, so currently these
		923	functions are not suitable for persistent hash tables, as their result
		924	value can change between different versions of libecb.
		925
		926	=over
		927
		928	=item uintptr_t ecb_ptrmix (void *ptr)
		929
		930	Mixes the bits of a pointer so the result is suitable for hash table
		931	lookups. In other words, this hashes the pointer value.
		932
		933	=item uintptr_t ecb_ptrmix (T *ptr) [C++]
		934
		935	Overload the C<ecb_ptrmix> function to work for any pointer in C++.
		936
		937	=item void *ecb_ptrunmix (uintptr_t v)
		938
		939	Unmix the hash value into the original pointer. This only works as long
		940	as the hash value is not truncated, i.e. you used C<uintptr_t> (or
		941	equivalent) throughout to store it.
		942
		943	=item T *ecb_ptrunmix<T> (uintptr_t v) [C++]
		944
		945	The somewhat less useful template version of C<ecb_ptrunmix> for
		946	C++. Example:
		947
		948	sometype *myptr;
		949	uintptr_t hash = ecb_ptrmix (myptr);
		950	sometype *orig = ecb_ptrunmix<sometype> (hash);
		951
		952	=item uint32_t ecb_mix32 (uint32_t v)
		953
		954	=item uint64_t ecb_mix64 (uint64_t v)
		955
		956	Sometimes you don't have a pointer but an integer whose values are very
		957	badly distributed. In this case you can use these integer versions of the
		958	mixing function. No C++ template is provided currently.
		959
		960	=item uint32_t ecb_unmix32 (uint32_t v)
		961
		962	=item uint64_t ecb_unmix64 (uint64_t v)
		963
		964	The reverse of the C<ecb_mix> functions - they take a mixed/hashed value
		965	and recover the original value.
		966
		967	=back
		968
		969	=head2 HOST ENDIANNESS CONVERSION
		970
		971	=over
		972
		973	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		974
		975	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		976
		977	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		978
		979	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		980
		981	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		982
		983	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		984
		985	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		986
		987	The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>,
		988	where C<be> and C<le> stand for big endian and little endian, respectively.
		989
		990	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		991
		992	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		993
		994	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		995
		996	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		997
		998	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		999
		1000	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		1001
		1002	Like above, but converts I<from> host byte order to the specified
		1003	endianness.
		1004
		1005	=back
		1006
		1007	In C++ the following additional template functions are supported:
		1008
		1009	=over
		1010
		1011	=item T ecb_be_to_host (T v)
		1012
		1013	=item T ecb_le_to_host (T v)
		1014
		1015	=item T ecb_host_to_be (T v)
		1016
		1017	=item T ecb_host_to_le (T v)
		1018
		1019	=back
		1020
		1021	These functions work like their C counterparts, above, but use templates,
		1022	which make them useful in generic code.
		1023
		1024	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		1025	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		1026	again can be useful in generic code).
		1027
		1028	=head2 UNALIGNED LOAD/STORE
		1029
		1030	These function load or store unaligned multi-byte values.
		1031
		1032	=over
		1033
		1034	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		1035
		1036	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		1037
		1038	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		1039
		1040	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		1041	memory.
		1042
		1043	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		1044
		1045	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		1046
		1047	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		1048
		1049	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		1050
		1051	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		1052
		1053	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		1054
		1055	Like above, but additionally convert from big endian (C<be>) or little
		1056	endian (C<le>) byte order to host byte order while doing so.
		1057
		1058	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		1059
		1060	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		1061
		1062	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		1063
		1064	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		1065	memory.
		1066
		1067	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		1068
		1069	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		1070
		1071	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		1072
		1073	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		1074
		1075	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		1076
		1077	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		1078
		1079	Like above, but additionally convert from host byte order to big endian
		1080	(C<be>) or little endian (C<le>) byte order while doing so.
		1081
		1082	=back
		1083
		1084	In C++ the following additional template functions are supported:
		1085
		1086	=over
		1087
		1088	=item T ecb_peek<T> (const void *ptr)
		1089
		1090	=item T ecb_peek_be<T> (const void *ptr)
		1091
		1092	=item T ecb_peek_le<T> (const void *ptr)
		1093
		1094	=item T ecb_peek_u<T> (const void *ptr)
		1095
		1096	=item T ecb_peek_be_u<T> (const void *ptr)
		1097
		1098	=item T ecb_peek_le_u<T> (const void *ptr)
		1099
		1100	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		1101	32 or 64 bit value from memory, with optional conversion from big/little
		1102	endian.
		1103
		1104	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		1105
		1106	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		1107
		1108	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		1109
		1110	Unlike their C counterparts, these functions support 8 bit quantities
		1111	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		1112	all of which hopefully makes them more useful in generic code.
		1113
		1114	=item ecb_poke (void *ptr, T v)
		1115
		1116	=item ecb_poke_be (void *ptr, T v)
		1117
		1118	=item ecb_poke_le (void *ptr, T v)
		1119
		1120	=item ecb_poke_u (void *ptr, T v)
		1121
		1122	=item ecb_poke_be_u (void *ptr, T v)
		1123
		1124	=item ecb_poke_le_u (void *ptr, T v)
		1125
		1126	Again, similarly to their C counterparts, these functions store an
		1127	unsigned 8, 16, 32 or 64 bit value to memory, with optional conversion to
		1128	big/little endian.
		1129
		1130	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		1131
		1132	Unlike their C counterparts, these functions support 8 bit quantities
		1133	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		1134	all of which hopefully makes them more useful in generic code.
		1135
		1136	=back
		1137
		1138	=head2 FAST INTEGER TO STRING
		1139
		1140	Libecb defines a set of very fast integer to decimal string (or integer
		1141	to ASCII, short C<i2a>) functions. These work by converting the integer
		1142	to a fixed point representation and then successively multiplying out
		1143	the topmost digits. Unlike some other, also very fast, libraries, ecb's
		1144	algorithm should be completely branchless per digit, and does not rely on
		1145	the presence of special CPU functions (such as C<clz>).
		1146
		1147	There is a high level API that takes an C<int32_t>, C<uint32_t>,
		1148	C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
		1149	harder to use but supports slightly more formatting options.
		1150
		1151	=head3 HIGH LEVEL API
		1152
		1153	The high level API consists of four functions, one each for C<int32_t>,
		1154	C<uint32_t>, C<int64_t> and C<uint64_t>:
		1155
		1156	Example:
		1157
		1158	char buf[ECB_I2A_MAX_DIGITS + 1];
		1159	char *end = ecb_i2a_i32 (buf, 17262);
		1160	*end = 0;
		1161	// buf now contains "17262"
		1162
		1163	=over
		1164
		1165	=item ECB_I2A_I32_DIGITS (=11)
		1166
		1167	=item char *ecb_i2a_u32 (char *ptr, uint32_t value)
		1168
		1169	Takes an C<uint32_t> I<value> and formats it as a decimal number starting
		1170	at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
		1171	pointer to just after the generated string, where you would normally put
		1172	the terminating C<0> character. This function outputs the minimum number
		1173	of digits.
		1174
		1175	=item ECB_I2A_U32_DIGITS (=10)
		1176
		1177	=item char *ecb_i2a_i32 (char *ptr, int32_t value)
		1178
		1179	Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
		1180	sign if needed.
		1181
		1182	=item ECB_I2A_I64_DIGITS (=20)
		1183
		1184	=item char *ecb_i2a_u64 (char *ptr, uint64_t value)
		1185
		1186	=item ECB_I2A_U64_DIGITS (=21)
		1187
		1188	=item char *ecb_i2a_i64 (char *ptr, int64_t value)
		1189
		1190	Similar to their 32 bit counterparts, these take a 64 bit argument.
		1191
		1192	=item ECB_I2A_MAX_DIGITS (=21)
		1193
		1194	Instead of using a type specific length macro, you can just use
		1195	C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
		1196
		1197	=back
		1198
		1199	=head3 LOW-LEVEL API
		1200
		1201	The functions above use a number of low-level APIs which have some strict
		1202	limitations, but can be used as building blocks (studying C<ecb_i2a_i32>
		1203	and related functions is recommended).
		1204
		1205	There are three families of functions: functions that convert a number
		1206	to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
		1207	for "leading zeroes"), functions that generate up to N digits, skipping
		1208	leading zeroes (C<_N>), and functions that can generate more digits, but
		1209	the leading digit has limited range (C<_xN>).
		1210
		1211	None of the functions deal with negative numbers.
		1212
		1213	Example: convert an IP address in an C<uint32_t> into dotted-quad:
		1214
		1215	uint32_t ip = 0x0a000164; // 10.0.1.100
		1216	char ips[3 * 4 + 3 + 1];
		1217	char *ptr = ips;
		1218	ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
		1219	ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
		1220	ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
		1221	ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
		1222	printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
		1223
		1224	=over
		1225
		1226	=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit
		1227
		1228	=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit
		1229
		1230	=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit
		1231
		1232	=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit
		1233
		1234	=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit
		1235
		1236	=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit
		1237
		1238	=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit
		1239
		1240	=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit
		1241
		1242	The C<< ecb_i2a_0I<N> >> functions take an unsigned I<value> and convert
		1243	them to exactly I<N> digits, returning a pointer to the first character
		1244	after the digits. The I<value> must be in range. The functions marked with
		1245	I<32 bit> do their calculations internally in 32 bit, the ones marked with
		1246	I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
		1247	architectures (the high level API decides on 32 vs. 64 bit versions using
		1248	C<ECB_64BIT_NATIVE>).
		1249
		1250	=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit
		1251
		1252	=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit
		1253
		1254	=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit
		1255
		1256	=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit
		1257
		1258	=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit
		1259
		1260	=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit
		1261
		1262	=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit
		1263
		1264	=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit
		1265
		1266	Similarly, the C<< ecb_i2a_I<N> >> functions take an unsigned I<value>
		1267	and convert them to at most I<N> digits, suppressing leading zeroes, and
		1268	returning a pointer to the first character after the digits.
		1269
		1270	=item ECB_I2A_MAX_X5 (=59074)
		1271
		1272	=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit
		1273
		1274	=item ECB_I2A_MAX_X10 (=2932500665)
		1275
		1276	=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit
		1277
		1278	The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >>
		1279	functions, but they can generate one digit more, as long as the number
		1280	is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
		1281	16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
		1282	respectively.
		1283
		1284	For example, the digit part of a 32 bit signed integer just fits into the
		1285	C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
		1286	digit number, it can convert all 32 bit signed numbers. Sadly, it's not
		1287	good enough for 32 bit unsigned numbers.
		1288
		1289	=back
		1290
		1291	=head2 FLOATING POINT FIDDLING
		1292
		1293	=over
		1294
		1295	=item ECB_INFINITY [-UECB_NO_LIBM]
		1296
		1297	Evaluates to positive infinity if supported by the platform, otherwise to
		1298	a truly huge number.
		1299
		1300	=item ECB_NAN [-UECB_NO_LIBM]
		1301
		1302	Evaluates to a quiet NAN if supported by the platform, otherwise to
		1303	C<ECB_INFINITY>.
		1304
		1305	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		1306
		1307	Same as C<ldexpf>, but always available.
		1308
		1309	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		1310
		1311	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		1312
		1313	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		1314
		1315	These functions each take an argument in the native C<float> or C<double>
		1316	type and return the IEEE 754 bit representation of it (binary16/half,
		1317	binary32/single or binary64/double precision).
		1318
		1319	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		1320	will be the most significant bit, followed by exponent and mantissa.
		1321
		1322	This function should work even when the native floating point format isn't
		1323	IEEE compliant, of course at a speed and code size penalty, and of course
		1324	also within reasonable limits (it tries to convert NaNs, infinities and
		1325	denormals, but will likely convert negative zero to positive zero).
		1326
		1327	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1328	be able to completely optimise away the 32 and 64 bit functions.
		1329
		1330	These functions can be helpful when serialising floats to the network - you
		1331	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		1332
		1333	Another use for these functions is to manipulate floating point values
		1334	directly.
		1335
		1336	Silly example: toggle the sign bit of a float.
		1337
		1338	/* On gcc-4.7 on amd64, */
		1339	/* this results in a single add instruction to toggle the bit, and 4 extra */
		1340	/* instructions to move the float value to an integer register and back. */
		1341
		1342	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		1343
		1344	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		1345
		1346	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		1347
		1348	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		1349
		1350	The reverse operation of the previous function - takes the bit
		1351	representation of an IEEE binary16, binary32 or binary64 number (half,
		1352	single or double precision) and converts it to the native C<float> or
		1353	C<double> format.
		1354
		1355	This function should work even when the native floating point format isn't
		1356	IEEE compliant, of course at a speed and code size penalty, and of course
		1357	also within reasonable limits (it tries to convert normals and denormals,
		1358	and might be lucky for infinities, and with extraordinary luck, also for
		1359	negative zero).
		1360
		1361	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		1362	be able to optimise away this function completely.
		1363
		1364	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		1365
		1366	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		1367
		1368	Convert a IEEE binary32/single precision to binary16/half format, and vice
		1369	versa, handling all details (round-to-nearest-even, subnormals, infinity
		1370	and NaNs) correctly.
		1371
		1372	These are functions are available under C<-DECB_NO_LIBM>, since
		1373	they do not rely on the platform floating point format. The
		1374	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		1375	usually what you want.
125		1376
126	=back	1377	=back
127		1378
128	=head2 ARITHMETIC	1379	=head2 ARITHMETIC
129		1380
130	=over 4	1381	=over
131		1382
132	=item x = ecb_mod (m, n) [MACRO]	1383	=item x = ecb_mod (m, n)
		1384
		1385	Returns C<m> modulo C<n>, which is the same as the positive remainder
		1386	of the division operation between C<m> and C<n>, using floored
		1387	division. Unlike the C remainder operator C<%>, this function ensures that
		1388	the return value is always positive and that the two numbers I<m> and
		1389	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		1390	C<ecb_mod> implements the mathematical modulo operation, which is missing
		1391	in the language.
		1392
		1393	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
		1394	negatable, that is, both C<m> and C<-m> must be representable in its
		1395	type (this typically excludes the minimum signed integer value, the same
		1396	limitation as for C</> and C<%> in C).
		1397
		1398	Current GCC/clang versions compile this into an efficient branchless
		1399	sequence on almost all CPUs.
		1400
		1401	For example, when you want to rotate forward through the members of an
		1402	array for increasing C<m> (which might be negative), then you should use
		1403	C<ecb_mod>, as the C<%> operator might give either negative results, or
		1404	change direction for negative values:
		1405
		1406	for (m = -100; m <= 100; ++m)
		1407	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		1408
		1409	=item x = ecb_div_rd (val, div)
		1410
		1411	=item x = ecb_div_ru (val, div)
		1412
		1413	Returns C<val> divided by C<div> rounded down or up, respectively.
		1414	C<val> and C<div> must have integer types and C<div> must be strictly
		1415	positive. Note that these functions are implemented with macros in C
		1416	and with function templates in C++.
133		1417
134	=back	1418	=back
135		1419
136	=head2 UTILITY	1420	=head2 UTILITY
137		1421
138	=over 4	1422	=over
139		1423
140	=item ecb_array_length (name) [MACRO]	1424	=item element_count = ecb_array_length (name)
141		1425
142	=back	1426	Returns the number of elements in the array C<name>. For example:
143		1427
		1428	int primes[] = { 2, 3, 5, 7, 11 };
		1429	int sum = 0;
144		1430
		1431	for (i = 0; i < ecb_array_length (primes); i++)
		1432	sum += primes [i];
		1433
		1434	=back
		1435
		1436	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
		1437
		1438	These symbols need to be defined before including F<ecb.h> the first time.
		1439
		1440	=over
		1441
		1442	=item ECB_NO_THREADS
		1443
		1444	If F<ecb.h> is never used from multiple threads, then this symbol can
		1445	be defined, in which case memory fences (and similar constructs) are
		1446	completely removed, leading to more efficient code and fewer dependencies.
		1447
		1448	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1449
		1450	=item ECB_NO_SMP
		1451
		1452	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1453	multiple threads, but never concurrently (e.g. if the system the program
		1454	runs on has only a single CPU with a single core, no hyper-threading and so
		1455	on), then this symbol can be defined, leading to more efficient code and
		1456	fewer dependencies.
		1457
		1458	=item ECB_NO_LIBM
		1459
		1460	When defined to C<1>, do not export any functions that might introduce
		1461	dependencies on the math library (usually called F<-lm>) - these are
		1462	marked with [-UECB_NO_LIBM].
		1463
		1464	=back
		1465
		1466	=head1 UNDOCUMENTED FUNCTIONALITY
		1467
		1468	F<ecb.h> is full of undocumented functionality as well, some of which is
		1469	intended to be internal-use only, some of which we forgot to document, and
		1470	some of which we hide because we are not sure we will keep the interface
		1471	stable.
		1472
		1473	While you are welcome to rummage around and use whatever you find useful
		1474	(we don't want to stop you), keep in mind that we will change undocumented
		1475	functionality in incompatible ways without thinking twice, while we are
		1476	considerably more conservative with documented things.
		1477
		1478	=head1 AUTHORS
		1479
		1480	C<libecb> is designed and maintained by:
		1481
		1482	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1483	Marc Alexander Lehmann <schmorp@schmorp.de>

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