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Revision 1.27 by root, Wed Jun 1 01:29:36 2011 UTC vs.
Revision 1.85 by root, Mon Jan 20 21:13:38 2020 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 into any standard C system,	20	Or in other words, things that should be built into any standard C
21	but aren't, implemented as efficient as possible with GCC, and still	21	system, but aren't, implemented as efficient as possible with GCC (clang,
22	correct with other compilers.	22	msvc...), and still correct with other compilers.
23		23
24	More might come.	24	More might come.
25		25
26	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
27		27
…		…
54	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
55	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
56	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
57	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
58		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 4
		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_AMD64, ECB_AMD64_X32
		170
		171	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		172	ABI, respectively, and undefined elsewhere.
		173
		174	The designers of the new X32 ABI for some inexplicable reason decided to
		175	make it look exactly like amd64, even though it's completely incompatible
		176	to that ABI, breaking about every piece of software that assumed that
		177	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		178	necessary.
		179
		180	=back
		181
		182	=head2 MACRO TRICKERY
		183
		184	=over 4
		185
		186	=item ECB_CONCAT (a, b)
		187
		188	Expands any macros in C<a> and C<b>, then concatenates the result to form
		189	a single token. This is mainly useful to form identifiers from components,
		190	e.g.:
		191
		192	#define S1 str
		193	#define S2 cpy
		194
		195	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		196
		197	=item ECB_STRINGIFY (arg)
		198
		199	Expands any macros in C<arg> and returns the stringified version of
		200	it. This is mainly useful to get the contents of a macro in string form,
		201	e.g.:
		202
		203	#define SQL_LIMIT 100
		204	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		205
		206	=item ECB_STRINGIFY_EXPR (expr)
		207
		208	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		209	is a valid expression. This is useful to catch typos or cases where the
		210	macro isn't available:
		211
		212	#include <errno.h>
		213
		214	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		215	ECB_STRINGIFY_EXPR (EDOM); // "33"
		216
		217	// now imagine we had a typo:
		218
		219	ECB_STRINGIFY (EDAM); // "EDAM"
		220	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		221
		222	=back
		223
59	=head2 GCC ATTRIBUTES	224	=head2 ATTRIBUTES
60		225
61	A major part of libecb deals with GCC attributes. These are additional	226	A major part of libecb deals with additional attributes that can be
62	attributes that you can assign to functions, variables and sometimes even	227	assigned to functions, variables and sometimes even types - much like
63	types - much like C<const> or C<volatile> in C.	228	C<const> or C<volatile> in C. They are implemented using either GCC
64		229	attributes or other compiler/language specific features. Attributes
65	While GCC allows declarations to show up in many surprising places,
66	but not in many expected places, the safest way is to put attribute
67	declarations before the whole declaration:	230	declarations must be put before the whole declaration:
68		231
69	ecb_const int mysqrt (int a);	232	ecb_const int mysqrt (int a);
70	ecb_unused int i;	233	ecb_unused int i;
71		234
72	For variables, it is often nicer to put the attribute after the name, and
73	avoid multiple declarations using commas:
74
75	int i ecb_unused;
76
77	=over 4	235	=over 4
78
79	=item ecb_attribute ((attrs...))
80
81	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
82	nothing on other compilers, so the effect is that only GCC sees these.
83
84	Example: use the C<deprecated> attribute on a function.
85
86	ecb_attribute((__deprecated__)) void
87	do_not_use_me_anymore (void);
88		236
89	=item ecb_unused	237	=item ecb_unused
90		238
91	Marks a function or a variable as "unused", which simply suppresses a	239	Marks a function or a variable as "unused", which simply suppresses a
92	warning by GCC when it detects it as unused. This is useful when you e.g.	240	warning by the compiler when it detects it as unused. This is useful when
93	declare a variable but do not always use it:	241	you e.g. declare a variable but do not always use it:
94		242
95	{	243	{
96	int var ecb_unused;	244	ecb_unused int var;
97		245
98	#ifdef SOMECONDITION	246	#ifdef SOMECONDITION
99	var = ...;	247	var = ...;
100	return var;	248	return var;
101	#else	249	#else
102	return 0;	250	return 0;
103	#endif	251	#endif
104	}	252	}
105		253
		254	=item ecb_deprecated
		255
		256	Similar to C<ecb_unused>, but marks a function, variable or type as
		257	deprecated. This makes some compilers warn when the type is used.
		258
		259	=item ecb_deprecated_message (message)
		260
		261	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		262	used instead of a generic depreciation message when the object is being
		263	used.
		264
		265	=item ecb_inline
		266
		267	Expands either to (a compiler-specific equivalent of) C<static inline> or
		268	to just C<static>, if inline isn't supported. It should be used to declare
		269	functions that should be inlined, for code size or speed reasons.
		270
		271	Example: inline this function, it surely will reduce codesize.
		272
		273	ecb_inline int
		274	negmul (int a, int b)
		275	{
		276	return - (a * b);
		277	}
		278
106	=item ecb_noinline	279	=item ecb_noinline
107		280
108	Prevent a function from being inlined - it might be optimised away, but	281	Prevents a function from being inlined - it might be optimised away, but
109	not inlined into other functions. This is useful if you know your function	282	not inlined into other functions. This is useful if you know your function
110	is rarely called and large enough for inlining not to be helpful.	283	is rarely called and large enough for inlining not to be helpful.
111		284
112	=item ecb_noreturn	285	=item ecb_noreturn
113		286
…		…
123	}	296	}
124		297
125	In this case, the compiler would probably be smart enough to deduce it on	298	In this case, the compiler would probably be smart enough to deduce it on
126	its own, so this is mainly useful for declarations.	299	its own, so this is mainly useful for declarations.
127		300
		301	=item ecb_restrict
		302
		303	Expands to the C<restrict> keyword or equivalent on compilers that support
		304	them, and to nothing on others. Must be specified on a pointer type or
		305	an array index to indicate that the memory doesn't alias with any other
		306	restricted pointer in the same scope.
		307
		308	Example: multiply a vector, and allow the compiler to parallelise the
		309	loop, because it knows it doesn't overwrite input values.
		310
		311	void
		312	multiply (ecb_restrict float *src,
		313	ecb_restrict float *dst,
		314	int len, float factor)
		315	{
		316	int i;
		317
		318	for (i = 0; i < len; ++i)
		319	dst [i] = src [i] * factor;
		320	}
		321
128	=item ecb_const	322	=item ecb_const
129		323
130	Declares that the function only depends on the values of its arguments,	324	Declares that the function only depends on the values of its arguments,
131	much like a mathematical function. It specifically does not read or write	325	much like a mathematical function. It specifically does not read or write
132	any memory any arguments might point to, global variables, or call any	326	any memory any arguments might point to, global variables, or call any
…		…
192	functions only called in exceptional or rare cases.	386	functions only called in exceptional or rare cases.
193		387
194	=item ecb_artificial	388	=item ecb_artificial
195		389
196	Declares the function as "artificial", in this case meaning that this	390	Declares the function as "artificial", in this case meaning that this
197	function is not really mean to be a function, but more like an accessor	391	function is not really meant to be a function, but more like an accessor
198	- many methods in C++ classes are mere accessor functions, and having a	392	- many methods in C++ classes are mere accessor functions, and having a
199	crash reported in such a method, or single-stepping through them, is not	393	crash reported in such a method, or single-stepping through them, is not
200	usually so helpful, especially when it's inlined to just a few instructions.	394	usually so helpful, especially when it's inlined to just a few instructions.
201		395
202	Marking them as artificial will instruct the debugger about just this,	396	Marking them as artificial will instruct the debugger about just this,
…		…
222		416
223	=head2 OPTIMISATION HINTS	417	=head2 OPTIMISATION HINTS
224		418
225	=over 4	419	=over 4
226		420
227	=item bool ecb_is_constant(expr)	421	=item bool ecb_is_constant (expr)
228		422
229	Returns true iff the expression can be deduced to be a compile-time	423	Returns true iff the expression can be deduced to be a compile-time
230	constant, and false otherwise.	424	constant, and false otherwise.
231		425
232	For example, when you have a C<rndm16> function that returns a 16 bit	426	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
250	return is_constant (n) && !(n & (n - 1))	444	return is_constant (n) && !(n & (n - 1))
251	? rndm16 () & (num - 1)	445	? rndm16 () & (num - 1)
252	: (n * (uint32_t)rndm16 ()) >> 16;	446	: (n * (uint32_t)rndm16 ()) >> 16;
253	}	447	}
254		448
255	=item bool ecb_expect (expr, value)	449	=item ecb_expect (expr, value)
256		450
257	Evaluates C<expr> and returns it. In addition, it tells the compiler that	451	Evaluates C<expr> and returns it. In addition, it tells the compiler that
258	the C<expr> evaluates to C<value> a lot, which can be used for static	452	the C<expr> evaluates to C<value> a lot, which can be used for static
259	branch optimisations.	453	branch optimisations.
260		454
…		…
307	{	501	{
308	if (ecb_expect_false (current + size > end))	502	if (ecb_expect_false (current + size > end))
309	real_reserve_method (size); /* presumably noinline */	503	real_reserve_method (size); /* presumably noinline */
310	}	504	}
311		505
312	=item bool ecb_assume (cond)	506	=item ecb_assume (cond)
313		507
314	Try to tell the compiler that some condition is true, even if it's not	508	Tries to tell the compiler that some condition is true, even if it's not
315	obvious.	509	obvious. This is not a function, but a statement: it cannot be used in
		510	another expression.
316		511
317	This can be used to teach the compiler about invariants or other	512	This can be used to teach the compiler about invariants or other
318	conditions that might improve code generation, but which are impossible to	513	conditions that might improve code generation, but which are impossible to
319	deduce form the code itself.	514	deduce form the code itself.
320		515
…		…
337		532
338	Then the compiler I<might> be able to optimise out the second call	533	Then the compiler I<might> be able to optimise out the second call
339	completely, as it knows that C<< current + 1 > end >> is false and the	534	completely, as it knows that C<< current + 1 > end >> is false and the
340	call will never be executed.	535	call will never be executed.
341		536
342	=item bool ecb_unreachable ()	537	=item ecb_unreachable ()
343		538
344	This function does nothing itself, except tell the compiler that it will	539	This function does nothing itself, except tell the compiler that it will
345	never be executed. Apart from suppressing a warning in some cases, this	540	never be executed. Apart from suppressing a warning in some cases, this
346	function can be used to implement C<ecb_assume> or similar functions.	541	function can be used to implement C<ecb_assume> or similar functionality.
347		542
348	=item bool ecb_prefetch (addr, rw, locality)	543	=item ecb_prefetch (addr, rw, locality)
349		544
350	Tells the compiler to try to prefetch memory at the given C<addr>ess	545	Tells the compiler to try to prefetch memory at the given C<addr>ess
351	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of	546	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
352	C<0> means that there will only be one access later, C<3> means that	547	C<0> means that there will only be one access later, C<3> means that
353	the data will likely be accessed very often, and values in between mean	548	the data will likely be accessed very often, and values in between mean
354	something... in between. The memory pointed to by the address does not	549	something... in between. The memory pointed to by the address does not
355	need to be accessible (it could be a null pointer for example), but C<rw>	550	need to be accessible (it could be a null pointer for example), but C<rw>
356	and C<locality> must be compile-time constants.	551	and C<locality> must be compile-time constants.
357		552
		553	This is a statement, not a function: you cannot use it as part of an
		554	expression.
		555
358	An obvious way to use this is to prefetch some data far away, in a big	556	An obvious way to use this is to prefetch some data far away, in a big
359	array you loop over. This prefetches memory some 128 array elements later,	557	array you loop over. This prefetches memory some 128 array elements later,
360	in the hope that it will be ready when the CPU arrives at that location.	558	in the hope that it will be ready when the CPU arrives at that location.
361		559
362	int sum = 0;	560	int sum = 0;
…		…
381	After processing the node, (part of) the next node might already be in	579	After processing the node, (part of) the next node might already be in
382	cache.	580	cache.
383		581
384	=back	582	=back
385		583
386	=head2 BIT FIDDLING / BITSTUFFS	584	=head2 BIT FIDDLING / BIT WIZARDRY
387		585
388	=over 4	586	=over 4
389		587
390	=item bool ecb_big_endian ()	588	=item bool ecb_big_endian ()
391		589
…		…
397		595
398	On systems that are neither, their return values are unspecified.	596	On systems that are neither, their return values are unspecified.
399		597
400	=item int ecb_ctz32 (uint32_t x)	598	=item int ecb_ctz32 (uint32_t x)
401		599
		600	=item int ecb_ctz64 (uint64_t x)
		601
		602	=item int ecb_ctz (T x) [C++]
		603
402	Returns the index of the least significant bit set in C<x> (or	604	Returns the index of the least significant bit set in C<x> (or
403	equivalently the number of bits set to 0 before the least significant bit	605	equivalently the number of bits set to 0 before the least significant bit
404	set), starting from 0. If C<x> is 0 the result is undefined. A common use	606	set), starting from 0. If C<x> is 0 the result is undefined.
405	case is to compute the integer binary logarithm, i.e., C<floor (log2	607
		608	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		609
		610	The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
		611	C<uint32_t> and C<uint64_t> types.
		612
406	(n))>. For example:	613	For example:
407		614
408	ecb_ctz32 (3) = 0	615	ecb_ctz32 (3) = 0
409	ecb_ctz32 (6) = 1	616	ecb_ctz32 (6) = 1
410		617
		618	=item bool ecb_is_pot32 (uint32_t x)
		619
		620	=item bool ecb_is_pot64 (uint32_t x)
		621
		622	=item bool ecb_is_pot (T x) [C++]
		623
		624	Returns true iff C<x> is a power of two or C<x == 0>.
		625
		626	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
		627
		628	The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
		629	C<uint32_t> and C<uint64_t> types.
		630
		631	=item int ecb_ld32 (uint32_t x)
		632
		633	=item int ecb_ld64 (uint64_t x)
		634
		635	=item int ecb_ld64 (T x) [C++]
		636
		637	Returns the index of the most significant bit set in C<x>, or the number
		638	of digits the number requires in binary (so that C<< 2**ld <= x <
		639	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		640	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		641	example to see how many bits a certain number requires to be encoded.
		642
		643	This function is similar to the "count leading zero bits" function, except
		644	that that one returns how many zero bits are "in front" of the number (in
		645	the given data type), while C<ecb_ld> returns how many bits the number
		646	itself requires.
		647
		648	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		649
		650	The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
		651	C<uint32_t> and C<uint64_t> types.
		652
411	=item int ecb_popcount32 (uint32_t x)	653	=item int ecb_popcount32 (uint32_t x)
412		654
		655	=item int ecb_popcount64 (uint64_t x)
		656
		657	=item int ecb_popcount (T x) [C++]
		658
413	Returns the number of bits set to 1 in C<x>. For example:	659	Returns the number of bits set to 1 in C<x>.
		660
		661	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		662
		663	The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
		664	C<uint32_t> and C<uint64_t> types.
		665
		666	For example:
414		667
415	ecb_popcount32 (7) = 3	668	ecb_popcount32 (7) = 3
416	ecb_popcount32 (255) = 8	669	ecb_popcount32 (255) = 8
417		670
		671	=item uint8_t ecb_bitrev8 (uint8_t x)
		672
		673	=item uint16_t ecb_bitrev16 (uint16_t x)
		674
		675	=item uint32_t ecb_bitrev32 (uint32_t x)
		676
		677	=item T ecb_bitrev (T x) [C++]
		678
		679	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		680	and so on.
		681
		682	The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
		683
		684	Example:
		685
		686	ecb_bitrev8 (0xa7) = 0xea
		687	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		688
		689	=item T ecb_bitrev (T x) [C++]
		690
		691	Overloaded C++ bitrev function.
		692
		693	C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
		694
418	=item uint32_t ecb_bswap16 (uint32_t x)	695	=item uint32_t ecb_bswap16 (uint32_t x)
419		696
420	=item uint32_t ecb_bswap32 (uint32_t x)	697	=item uint32_t ecb_bswap32 (uint32_t x)
421		698
		699	=item uint64_t ecb_bswap64 (uint64_t x)
		700
		701	=item T ecb_bswap (T x)
		702
422	These two functions return the value of the 16-bit (32-bit) value C<x>	703	These functions return the value of the 16-bit (32-bit, 64-bit) value
423	after reversing the order of bytes (0x11223344 becomes 0x44332211).	704	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		705	C<ecb_bswap32>).
		706
		707	The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
		708	C<uint32_t> and C<uint64_t> types.
		709
		710	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		711
		712	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		713
		714	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		715
		716	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		717
		718	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		719
		720	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
424		721
425	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	722	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
426		723
427	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	724	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
428		725
429	These two functions return the value of C<x> after rotating all the bits	726	These two families of functions return the value of C<x> after rotating
430	by C<count> positions to the right or left respectively.	727	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		728	(C<ecb_rotl>).
431		729
432	Current GCC versions understand these functions and usually compile them	730	Current GCC/clang versions understand these functions and usually compile
433	to "optimal" code (e.g. a single C<roll> on x86).	731	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
		732	on x86).
		733
		734	=item T ecb_rotl (T x, unsigned int count) [C++]
		735
		736	=item T ecb_rotr (T x, unsigned int count) [C++]
		737
		738	Overloaded C++ rotl/rotr functions.
		739
		740	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		741
		742	=back
		743
		744	=head2 HOST ENDIANNESS CONVERSION
		745
		746	=over 4
		747
		748	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
		749
		750	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
		751
		752	=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
		753
		754	=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
		755
		756	=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
		757
		758	=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
		759
		760	Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
		761
		762	The naming convention is C<ecb_>(C<be>\|C<le>)C<_u>C<16\|32\|64>C<_to_host>,
		763	where C<be> and C<le> stand for big endian and little endian, respectively.
		764
		765	=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
		766
		767	=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
		768
		769	=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
		770
		771	=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
		772
		773	=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
		774
		775	=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
		776
		777	Like above, but converts I<from> host byte order to the specified
		778	endianness.
		779
		780	=back
		781
		782	In C++ the following additional template functions are supported:
		783
		784	=over 4
		785
		786	=item T ecb_be_to_host (T v)
		787
		788	=item T ecb_le_to_host (T v)
		789
		790	=item T ecb_host_to_be (T v)
		791
		792	=item T ecb_host_to_le (T v)
		793
		794	These functions work like their C counterparts, above, but use templates,
		795	which make them useful in generic code.
		796
		797	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
		798	(so unlike their C counterparts, there is a version for C<uint8_t>, which
		799	again can be useful in generic code).
		800
		801	=head2 UNALIGNED LOAD/STORE
		802
		803	These function load or store unaligned multi-byte values.
		804
		805	=over 4
		806
		807	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
		808
		809	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
		810
		811	=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
		812
		813	These functions load an unaligned, unsigned 16, 32 or 64 bit value from
		814	memory.
		815
		816	=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
		817
		818	=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
		819
		820	=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
		821
		822	=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
		823
		824	=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
		825
		826	=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
		827
		828	Like above, but additionally convert from big endian (C<be>) or little
		829	endian (C<le>) byte order to host byte order while doing so.
		830
		831	=item ecb_poke_u16_u (void *ptr, uint16_t v)
		832
		833	=item ecb_poke_u32_u (void *ptr, uint32_t v)
		834
		835	=item ecb_poke_u64_u (void *ptr, uint64_t v)
		836
		837	These functions store an unaligned, unsigned 16, 32 or 64 bit value to
		838	memory.
		839
		840	=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
		841
		842	=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
		843
		844	=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
		845
		846	=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
		847
		848	=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
		849
		850	=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
		851
		852	Like above, but additionally convert from host byte order to big endian
		853	(C<be>) or little endian (C<le>) byte order while doing so.
		854
		855	=back
		856
		857	In C++ the following additional template functions are supported:
		858
		859	=over 4
		860
		861	=item T ecb_peek<T> (const void *ptr)
		862
		863	=item T ecb_peek_be<T> (const void *ptr)
		864
		865	=item T ecb_peek_le<T> (const void *ptr)
		866
		867	=item T ecb_peek_u<T> (const void *ptr)
		868
		869	=item T ecb_peek_be_u<T> (const void *ptr)
		870
		871	=item T ecb_peek_le_u<T> (const void *ptr)
		872
		873	Similarly to their C counterparts, these functions load an unsigned 8, 16,
		874	32 or 64 bit value from memory, with optional conversion from big/little
		875	endian.
		876
		877	Since the type cannot be deduced, it has to be specified explicitly, e.g.
		878
		879	uint_fast16_t v = ecb_peek<uint16_t> (ptr);
		880
		881	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		882
		883	Unlike their C counterparts, these functions support 8 bit quantities
		884	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		885	all of which hopefully makes them more useful in generic code.
		886
		887	=item ecb_poke (void *ptr, T v)
		888
		889	=item ecb_poke_be (void *ptr, T v)
		890
		891	=item ecb_poke_le (void *ptr, T v)
		892
		893	=item ecb_poke_u (void *ptr, T v)
		894
		895	=item ecb_poke_be_u (void *ptr, T v)
		896
		897	=item ecb_poke_le_u (void *ptr, T v)
		898
		899	Again, similarly to their C counterparts, these functions store an
		900	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
		901	big/little endian.
		902
		903	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
		904
		905	Unlike their C counterparts, these functions support 8 bit quantities
		906	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
		907	all of which hopefully makes them more useful in generic code.
		908
		909	=back
		910
		911	=head2 FLOATING POINT FIDDLING
		912
		913	=over 4
		914
		915	=item ECB_INFINITY [-UECB_NO_LIBM]
		916
		917	Evaluates to positive infinity if supported by the platform, otherwise to
		918	a truly huge number.
		919
		920	=item ECB_NAN [-UECB_NO_LIBM]
		921
		922	Evaluates to a quiet NAN if supported by the platform, otherwise to
		923	C<ECB_INFINITY>.
		924
		925	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		926
		927	Same as C<ldexpf>, but always available.
		928
		929	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		930
		931	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		932
		933	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		934
		935	These functions each take an argument in the native C<float> or C<double>
		936	type and return the IEEE 754 bit representation of it (binary16/half,
		937	binary32/single or binary64/double precision).
		938
		939	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		940	will be the most significant bit, followed by exponent and mantissa.
		941
		942	This function should work even when the native floating point format isn't
		943	IEEE compliant, of course at a speed and code size penalty, and of course
		944	also within reasonable limits (it tries to convert NaNs, infinities and
		945	denormals, but will likely convert negative zero to positive zero).
		946
		947	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		948	be able to optimise away this function completely.
		949
		950	These functions can be helpful when serialising floats to the network - you
		951	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		952
		953	Another use for these functions is to manipulate floating point values
		954	directly.
		955
		956	Silly example: toggle the sign bit of a float.
		957
		958	/* On gcc-4.7 on amd64, */
		959	/* this results in a single add instruction to toggle the bit, and 4 extra */
		960	/* instructions to move the float value to an integer register and back. */
		961
		962	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		963
		964	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		965
		966	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		967
		968	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		969
		970	The reverse operation of the previous function - takes the bit
		971	representation of an IEEE binary16, binary32 or binary64 number (half,
		972	single or double precision) and converts it to the native C<float> or
		973	C<double> format.
		974
		975	This function should work even when the native floating point format isn't
		976	IEEE compliant, of course at a speed and code size penalty, and of course
		977	also within reasonable limits (it tries to convert normals and denormals,
		978	and might be lucky for infinities, and with extraordinary luck, also for
		979	negative zero).
		980
		981	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		982	be able to optimise away this function completely.
		983
		984	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		985
		986	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		987
		988	Convert a IEEE binary32/single precision to binary16/half format, and vice
		989	versa, handling all details (round-to-nearest-even, subnormals, infinity
		990	and NaNs) correctly.
		991
		992	These are functions are available under C<-DECB_NO_LIBM>, since
		993	they do not rely on the platform floating point format. The
		994	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		995	usually what you want.
434		996
435	=back	997	=back
436		998
437	=head2 ARITHMETIC	999	=head2 ARITHMETIC
438		1000
…		…
448	C<ecb_mod> implements the mathematical modulo operation, which is missing	1010	C<ecb_mod> implements the mathematical modulo operation, which is missing
449	in the language.	1011	in the language.
450		1012
451	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be	1013	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
452	negatable, that is, both C<m> and C<-m> must be representable in its	1014	negatable, that is, both C<m> and C<-m> must be representable in its
453	type (this typically includes the minimum signed integer value, the same	1015	type (this typically excludes the minimum signed integer value, the same
454	limitation as for C</> and C<%> in C).	1016	limitation as for C</> and C<%> in C).
455		1017
456	Current GCC versions compile this into an efficient branchless sequence on	1018	Current GCC/clang versions compile this into an efficient branchless
457	many systems.	1019	sequence on almost all CPUs.
458		1020
459	For example, when you want to rotate forward through the members of an	1021	For example, when you want to rotate forward through the members of an
460	array for increasing C<m> (which might be negative), then you should use	1022	array for increasing C<m> (which might be negative), then you should use
461	C<ecb_mod>, as the C<%> operator might give either negative results, or	1023	C<ecb_mod>, as the C<%> operator might give either negative results, or
462	change direction for negative values:	1024	change direction for negative values:
463		1025
464	for (m = -100; m <= 100; ++m)	1026	for (m = -100; m <= 100; ++m)
465	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];	1027	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
466		1028
		1029	=item x = ecb_div_rd (val, div)
		1030
		1031	=item x = ecb_div_ru (val, div)
		1032
		1033	Returns C<val> divided by C<div> rounded down or up, respectively.
		1034	C<val> and C<div> must have integer types and C<div> must be strictly
		1035	positive. Note that these functions are implemented with macros in C
		1036	and with function templates in C++.
		1037
467	=back	1038	=back
468		1039
469	=head2 UTILITY	1040	=head2 UTILITY
470		1041
471	=over 4	1042	=over 4
…		…
480	for (i = 0; i < ecb_array_length (primes); i++)	1051	for (i = 0; i < ecb_array_length (primes); i++)
481	sum += primes [i];	1052	sum += primes [i];
482		1053
483	=back	1054	=back
484		1055
		1056	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
485		1057
		1058	These symbols need to be defined before including F<ecb.h> the first time.
		1059
		1060	=over 4
		1061
		1062	=item ECB_NO_THREADS
		1063
		1064	If F<ecb.h> is never used from multiple threads, then this symbol can
		1065	be defined, in which case memory fences (and similar constructs) are
		1066	completely removed, leading to more efficient code and fewer dependencies.
		1067
		1068	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		1069
		1070	=item ECB_NO_SMP
		1071
		1072	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		1073	multiple threads, but never concurrently (e.g. if the system the program
		1074	runs on has only a single CPU with a single core, no hyperthreading and so
		1075	on), then this symbol can be defined, leading to more efficient code and
		1076	fewer dependencies.
		1077
		1078	=item ECB_NO_LIBM
		1079
		1080	When defined to C<1>, do not export any functions that might introduce
		1081	dependencies on the math library (usually called F<-lm>) - these are
		1082	marked with [-UECB_NO_LIBM].
		1083
		1084	=back
		1085
		1086	=head1 UNDOCUMENTED FUNCTIONALITY
		1087
		1088	F<ecb.h> is full of undocumented functionality as well, some of which is
		1089	intended to be internal-use only, some of which we forgot to document, and
		1090	some of which we hide because we are not sure we will keep the interface
		1091	stable.
		1092
		1093	While you are welcome to rummage around and use whatever you find useful
		1094	(we can't stop you), keep in mind that we will change undocumented
		1095	functionality in incompatible ways without thinking twice, while we are
		1096	considerably more conservative with documented things.
		1097
		1098	=head1 AUTHORS
		1099
		1100	C<libecb> is designed and maintained by:
		1101
		1102	Emanuele Giaquinta <e.giaquinta@glauco.it>
		1103	Marc Alexander Lehmann <schmorp@schmorp.de>
		1104
		1105

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Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.27 by root, Wed Jun 1 01:29:36 2011 UTC vs.
Revision 1.85 by root, Mon Jan 20 21:13:38 2020 UTC