[ViewVC] Diff of: cvs/libecb/ecb.pod

Comparing libecb/ecb.pod (file contents):
Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC vs.
Revision 1.104 by root, Fri Mar 25 08:44:14 2022 UTC

…		…
10		10
11	Its homepage can be found here:	11	Its homepage can be found here:
12		12
13	http://software.schmorp.de/pkg/libecb	13	http://software.schmorp.de/pkg/libecb
14		14
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around many compiler built-ins,
16	with replacement functions for other compilers. In addition to this,	16	together with replacement functions for other compilers. In addition
17	it provides a number of other lowlevel C utilities, such as endianness	17	to this, it provides a number of other low-level 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
…		…
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	59	=head2 TYPES / TYPE SUPPORT
60		60
61	ecb.h makes sure that the following types are defined (in the expected way):	61	F<ecb.h> makes sure that the following types are defined (in the expected way):
62		62
63	int8_t uint8_	63	int8_t uint8_
64	int16_t uint16_t	64	int16_t uint16_t
65	int32_t uint32_	65	int32_t uint32_
66	int64_t uint64_t	66	int64_t uint64_t
…		…
80		80
81	All the following symbols expand to an expression that can be tested in	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	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).	83	ensure it's either C<0> or C<1> if you need that).
84		84
85	=over 4	85	=over
86		86
87	=item ECB_C	87	=item ECB_C
88		88
89	True if the implementation defines the C<__STDC__> macro to a true value,	89	True if the implementation defines the C<__STDC__> macro to a true value,
90	while not claiming to be C++.	90	while not claiming to be C++, i..e C, but not C++.
91		91
92	=item ECB_C99	92	=item ECB_C99
93		93
94	True if the implementation claims to be compliant to C99 (ISO/IEC	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++.	95	9899:1999) or any later version, while not claiming to be C++.
…		…
109		109
110	=item ECB_CPP11, ECB_CPP14, ECB_CPP17	110	=item ECB_CPP11, ECB_CPP14, ECB_CPP17
111		111
112	True if the implementation claims to be compliant to C++11/C++14/C++17	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.	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>).
114		117
115	=item ECB_OPTIMIZE_SIZE	118	=item ECB_OPTIMIZE_SIZE
116		119
117	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol	120	Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
118	can also be defined before including F<ecb.h>, in which case it will be	121	can also be defined before including F<ecb.h>, in which case it will be
119	unchanged.	122	unchanged.
120		123
121	=item ECB_GCC_VERSION (major, minor)	124	=item ECB_GCC_VERSION (major, minor)
122		125
123	Expands to a true value (suitable for testing in by the preprocessor)	126	Expands to a true value (suitable for testing by the preprocessor) if the
124	if the compiler used is GNU C and the version is the given version, or	127	compiler used is GNU C and the version is the given version, or higher.
125	higher.
126		128
127	This macro tries to return false on compilers that claim to be GCC	129	This macro tries to return false on compilers that claim to be GCC
128	compatible but aren't.	130	compatible but aren't.
129		131
130	=item ECB_EXTERN_C	132	=item ECB_EXTERN_C
…		…
149		151
150	ECB_EXTERN_C_END	152	ECB_EXTERN_C_END
151		153
152	=item ECB_STDFP	154	=item ECB_STDFP
153		155
154	If this evaluates to a true value (suitable for testing in by the	156	If this evaluates to a true value (suitable for testing by the
155	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32	157	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
156	and double/binary64 representations internally I<and> the endianness of	158	and double/binary64 representations internally I<and> the endianness of
157	both types match the endianness of C<uint32_t> and C<uint64_t>.	159	both types match the endianness of C<uint32_t> and C<uint64_t>.
158		160
159	This means you can just copy the bits of a C<float> (or C<double>) to an	161	This means you can just copy the bits of a C<float> (or C<double>) to an
…		…
161	without having to think about format or endianness.	163	without having to think about format or endianness.
162		164
163	This is true for basically all modern platforms, although F<ecb.h> might	165	This is true for basically all modern platforms, although F<ecb.h> might
164	not be able to deduce this correctly everywhere and might err on the safe	166	not be able to deduce this correctly everywhere and might err on the safe
165	side.	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.
166		176
167	=item ECB_AMD64, ECB_AMD64_X32	177	=item ECB_AMD64, ECB_AMD64_X32
168		178
169	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32	179	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
170	ABI, respectively, and undefined elsewhere.	180	ABI, respectively, and undefined elsewhere.
…		…
177		187
178	=back	188	=back
179		189
180	=head2 MACRO TRICKERY	190	=head2 MACRO TRICKERY
181		191
182	=over 4	192	=over
183		193
184	=item ECB_CONCAT (a, b)	194	=item ECB_CONCAT (a, b)
185		195
186	Expands any macros in C<a> and C<b>, then concatenates the result to form	196	Expands any macros in C<a> and C<b>, then concatenates the result to form
187	a single token. This is mainly useful to form identifiers from components,	197	a single token. This is mainly useful to form identifiers from components,
…		…
228	declarations must be put before the whole declaration:	238	declarations must be put before the whole declaration:
229		239
230	ecb_const int mysqrt (int a);	240	ecb_const int mysqrt (int a);
231	ecb_unused int i;	241	ecb_unused int i;
232		242
233	=over 4	243	=over
234		244
235	=item ecb_unused	245	=item ecb_unused
236		246
237	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
238	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
239	declare a variable but do not always use it:	249	you e.g. declare a variable but do not always use it:
240		250
241	{	251	{
242	ecb_unused int var;	252	ecb_unused int var;
243		253
244	#ifdef SOMECONDITION	254	#ifdef SOMECONDITION
…		…
264		274
265	Expands either to (a compiler-specific equivalent of) C<static inline> or	275	Expands either to (a compiler-specific equivalent of) C<static inline> or
266	to just C<static>, if inline isn't supported. It should be used to declare	276	to just C<static>, if inline isn't supported. It should be used to declare
267	functions that should be inlined, for code size or speed reasons.	277	functions that should be inlined, for code size or speed reasons.
268		278
269	Example: inline this function, it surely will reduce codesize.	279	Example: inline this function, it surely will reduce code size.
270		280
271	ecb_inline int	281	ecb_inline int
272	negmul (int a, int b)	282	negmul (int a, int b)
273	{	283	{
274	return - (a * b);	284	return - (a * b);
…		…
374	speed-critical times, and keeping it in the cache might be a waste of said	384	speed-critical times, and keeping it in the cache might be a waste of said
375	cache.	385	cache.
376		386
377	In addition to placing cold functions together (or at least away from hot	387	In addition to placing cold functions together (or at least away from hot
378	functions), this knowledge can be used in other ways, for example, the	388	functions), this knowledge can be used in other ways, for example, the
379	function will be optimised for size, as opposed to speed, and codepaths	389	function will be optimised for size, as opposed to speed, and code paths
380	leading to calls to those functions can automatically be marked as if	390	leading to calls to those functions can automatically be marked as if
381	C<ecb_expect_false> had been used to reach them.	391	C<ecb_expect_false> had been used to reach them.
382		392
383	Good examples for such functions would be error reporting functions, or	393	Good examples for such functions would be error reporting functions, or
384	functions only called in exceptional or rare cases.	394	functions only called in exceptional or rare cases.
…		…
412		422
413	=back	423	=back
414		424
415	=head2 OPTIMISATION HINTS	425	=head2 OPTIMISATION HINTS
416		426
417	=over 4	427	=over
418		428
419	=item bool ecb_is_constant (expr)	429	=item bool ecb_is_constant (expr)
420		430
421	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
422	constant, and false otherwise.	432	constant, and false otherwise.
…		…
538	never be executed. Apart from suppressing a warning in some cases, this	548	never be executed. Apart from suppressing a warning in some cases, this
539	function can be used to implement C<ecb_assume> or similar functionality.	549	function can be used to implement C<ecb_assume> or similar functionality.
540		550
541	=item ecb_prefetch (addr, rw, locality)	551	=item ecb_prefetch (addr, rw, locality)
542		552
543	Tells the compiler to try to prefetch memory at the given C<addr>ess	553	Tells the compiler to try to prefetch memory at the given I<addr>ess
544	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of	554	for either reading (I<rw> = 0) or writing (I<rw> = 1). A I<locality> of
545	C<0> means that there will only be one access later, C<3> means that	555	C<0> means that there will only be one access later, C<3> means that
546	the data will likely be accessed very often, and values in between mean	556	the data will likely be accessed very often, and values in between mean
547	something... in between. The memory pointed to by the address does not	557	something... in between. The memory pointed to by the address does not
548	need to be accessible (it could be a null pointer for example), but C<rw>	558	need to be accessible (it could be a null pointer for example), but C<rw>
549	and C<locality> must be compile-time constants.	559	and C<locality> must be compile-time constants.
…		…
579		589
580	=back	590	=back
581		591
582	=head2 BIT FIDDLING / BIT WIZARDRY	592	=head2 BIT FIDDLING / BIT WIZARDRY
583		593
584	=over 4	594	=over
585		595
586	=item bool ecb_big_endian ()	596	=item bool ecb_big_endian ()
587		597
588	=item bool ecb_little_endian ()	598	=item bool ecb_little_endian ()
589		599
…		…
721		731
722	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)	732	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
723		733
724	These two families of functions return the value of C<x> after rotating	734	These two families of functions return the value of C<x> after rotating
725	all the bits by C<count> positions to the right (C<ecb_rotr>) or left	735	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
726	(C<ecb_rotl>).	736	(C<ecb_rotl>). There are no restrictions on the value C<count>, i.e. both
		737	zero and values equal or larger than the word width work correctly. Also,
		738	notwithstanding C<count> being unsigned, negative numbers work and shift
		739	to the opposite direction.
727		740
728	Current GCC versions understand these functions and usually compile them	741	Current GCC/clang versions understand these functions and usually compile
729	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on	742	them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
730	x86).	743	on x86).
731		744
732	=item T ecb_rotl (T x, unsigned int count) [C++]	745	=item T ecb_rotl (T x, unsigned int count) [C++]
733		746
734	=item T ecb_rotr (T x, unsigned int count) [C++]	747	=item T ecb_rotr (T x, unsigned int count) [C++]
735		748
736	Overloaded C++ rotl/rotr functions.	749	Overloaded C++ rotl/rotr functions.
737		750
738	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.	751	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
739		752
		753	=item uint_fast8_t ecb_gray8_encode (uint_fast8_t b)
		754
		755	=item uint_fast16_t ecb_gray16_encode (uint_fast16_t b)
		756
		757	=item uint_fast32_t ecb_gray32_encode (uint_fast32_t b)
		758
		759	=item uint_fast64_t ecb_gray64_encode (uint_fast64_t b)
		760
		761	Encode an unsigned into its corresponding (reflective) gray code - the
		762	kind of gray code meant when just talking about "gray code". These
		763	functions are very fast and all have identical implementation, so there is
		764	no need to use a smaller type, as long as your CPU can handle it natively.
		765
		766	=item T ecb_gray_encode (T b) [C++]
		767
		768	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		769
		770	=item uint_fast8_t ecb_gray8_decode (uint_fast8_t b)
		771
		772	=item uint_fast16_t ecb_gray16_decode (uint_fast16_t b)
		773
		774	=item uint_fast32_t ecb_gray32_decode (uint_fast32_t b)
		775
		776	=item uint_fast64_t ecb_gray64_decode (uint_fast64_t b)
		777
		778	Decode a gray code back into linear index form (the reverse of
		779	C<ecb_gray*_encode>. Unlike the encode functions, the decode functions
		780	have higher time complexity for larger types, so it can pay off to use a
		781	smaller type here.
		782
		783	=item T ecb_gray_decode (T b) [C++]
		784
		785	Overloaded C++ version of the above, for C<uint{8,16,32,64}_t>.
		786
		787	=back
		788
		789	=head2 HILBERT CURVES
		790
		791	These functions deal with (square, pseudo) Hilbert curves. The parameter
		792	I<order> indicates the size of the square and is specified in bits, that
		793	means for order C<8>, the coordinates range from C<0>..C<255>, and the
		794	curve index ranges from C<0>..C<65535>.
		795
		796	The 32 bit variants of these functions map a 32 bit index to two 16 bit
		797	coordinates, stored in a 32 bit variable, where the high order bits are
		798	the x-coordinate, and the low order bits are the y-coordinate, thus,
		799	these functions map 32 bit linear index on the curve to a 32 bit packed
		800	coordinate pair, and vice versa.
		801
		802	The 64 bit variants work similarly.
		803
		804	The I<order> can go from C<1> to C<16> for the 32 bit curve, and C<1> to
		805	C<32> for the 64 bit curve.
		806
		807	When going from one order to the next higher order, these functions
		808	replace the curve segments by smaller versions of the generating shape,
		809	while doubling the size (since they use integer coordinates), which is
		810	what you would expect mathematically. This means that the curve will be
		811	mirrored at the diagonal. If your goal is to simply cover more area while
		812	retaining existing point coordinates you should increase or decrease the
		813	I<order> by C<2> or, in the case of C<ecb_hilbert2d_index_to_coord>,
		814	simply specify the maximum I<order> of C<16> or C<32>, respectively, as
		815	these are constant-time.
		816
		817	=over
		818
		819	=item uint32_t ecb_hilbert2d_index_to_coord32 (int order, uint32_t index)
		820
		821	=item uint64_t ecb_hilbert2d_index_to_coord64 (int order, uint64_t index)
		822
		823	Map a point on a pseudo Hilbert curve from its linear distance from the
		824	origin on the curve to a x\|y coordinate pair. The result is a packed
		825	coordinate pair, to get the actual x and < coordinates, you could do
		826	something like this:
		827
		828	uint32_t xy = ecb_hilbert2d_index_to_coord32 (16, 255);
		829	uint16_t x = xy >> 16;
		830	uint16_t y = xy & 0xffffU;
		831
		832	uint64_t xy = ecb_hilbert2d_index_to_coord64 (32, 255);
		833	uint32_t x = xy >> 32;
		834	uint32_t y = xy & 0xffffffffU;
		835
		836	These functions work in constant time, so for many applications it is
		837	preferable to simply hard-code the order to the maximum (C<16> or C<32>).
		838
		839	This (production-ready, i.e. never run) example generates an SVG image of
		840	an order 8 pseudo Hilbert curve:
		841
		842	printf ("<svg xmlns='http://www.w3.org/2000/svg' width='%d' height='%d'>\n", 64 * 8, 64 * 8);
		843	printf ("<g transform='translate(4) scale(8)' stroke-width='0.25' stroke='black'>\n");
		844	for (uint32_t i = 0; i < 64*64 - 1; ++i)
		845	{
		846	uint32_t p1 = ecb_hilbert2d_index_to_coord32 (6, i );
		847	uint32_t p2 = ecb_hilbert2d_index_to_coord32 (6, i + 1);
		848	printf ("<line x1='%d' y1='%d' x2='%d' y2='%d'/>\n",
		849	p1 >> 16, p1 & 0xffff,
		850	p2 >> 16, p2 & 0xffff);
		851	}
		852	printf ("</g>\n");
		853	printf ("</svg>\n");
		854
		855	=item uint32_t ecb_hilbert2d_coord_to_index32 (int order, uint32_t xy)
		856
		857	=item uint64_t ecb_hilbert2d_coord_to_index64 (int order, uint64_t xy)
		858
		859	The reverse of C<ecb_hilbert2d_index_to_coord> - map a packed pair of
		860	coordinates to their linear index on the pseudo Hilbert curve of order
		861	I<order>.
		862
		863	They are an exact inverse of the C<ecb_hilbert2d_coord_to_index> functions
		864	for the same I<order>:
		865
		866	assert (
		867	u == ecb_hilbert2d_coord_to_index (32,
		868	ecb_hilbert2d_index_to_coord32 (32,
		869	u)));
		870
		871	Packing coordinates is done the same way, as well, from I<x> and I<y>:
		872
		873	uint32_t xy = ((uint32_t)x << 16) \| y; // for ecb_hilbert2d_coord_to_index32
		874	uint64_t xy = ((uint64_t)x << 32) \| y; // for ecb_hilbert2d_coord_to_index64
		875
		876	Unlike C<ecb_hilbert2d_coord_to_index>, these functions are O(I<order>),
		877	so it is preferable to use the lowest possible order.
		878
		879	=back
		880
		881	=head2 BIT MIXING, HASHING
		882
		883	Sometimes you have an integer and want to distribute its bits well, for
		884	example, to use it as a hash in a hash table. A common example is pointer
		885	values, which often only have a limited range (e.g. low and high bits are
		886	often zero).
		887
		888	The following functions try to mix the bits to get a good bias-free
		889	distribution. They were mainly made for pointers, but the underlying
		890	integer functions are exposed as well.
		891
		892	As an added benefit, the functions are reversible, so if you find it
		893	convenient to store only the hash value, you can recover the original
		894	pointer from the hash ("unmix"), as long as your pointers are 32 or 64 bit
		895	(if this isn't the case on your platform, drop us a note and we will add
		896	functions for other bit widths).
		897
		898	The unmix functions are very slightly slower than the mix functions, so
		899	it is equally very slightly preferable to store the original values wehen
		900	convenient.
		901
		902	The underlying algorithm if subject to change, so currently these
		903	functions are not suitable for persistent hash tables, as their result
		904	value can change between different versions of libecb.
		905
		906	=over
		907
		908	=item uintptr_t ecb_ptrmix (void *ptr)
		909
		910	Mixes the bits of a pointer so the result is suitable for hash table
		911	lookups. In other words, this hashes the pointer value.
		912
		913	=item uintptr_t ecb_ptrmix (T *ptr) [C++]
		914
		915	Overload the C<ecb_ptrmix> function to work for any pointer in C++.
		916
		917	=item void *ecb_ptrunmix (uintptr_t v)
		918
		919	Unmix the hash value into the original pointer. This only works as long
		920	as the hash value is not truncated, i.e. you used C<uintptr_t> (or
		921	equivalent) throughout to store it.
		922
		923	=item T *ecb_ptrunmix<T> (uintptr_t v) [C++]
		924
		925	The somewhat less useful template version of C<ecb_ptrunmix> for
		926	C++. Example:
		927
		928	sometype *myptr;
		929	uintptr_t hash = ecb_ptrmix (myptr);
		930	sometype *orig = ecb_ptrunmix<sometype> (hash);
		931
		932	=item uint32_t ecb_mix32 (uint32_t v)
		933
		934	=item uint64_t ecb_mix64 (uint64_t v)
		935
		936	Sometimes you don't have a pointer but an integer whose values are very
		937	badly distributed. In this case you can use these integer versions of the
		938	mixing function. No C++ template is provided currently.
		939
		940	=item uint32_t ecb_unmix32 (uint32_t v)
		941
		942	=item uint64_t ecb_unmix64 (uint64_t v)
		943
		944	The reverse of the C<ecb_mix> functions - they take a mixed/hashed value
		945	and recover the original value.
		946
740	=back	947	=back
741		948
742	=head2 HOST ENDIANNESS CONVERSION	949	=head2 HOST ENDIANNESS CONVERSION
743		950
744	=over 4	951	=over
745		952
746	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)	953	=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
747		954
748	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)	955	=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
749		956
…		…
777		984
778	=back	985	=back
779		986
780	In C++ the following additional template functions are supported:	987	In C++ the following additional template functions are supported:
781		988
782	=over 4	989	=over
783		990
784	=item T ecb_be_to_host (T v)	991	=item T ecb_be_to_host (T v)
785		992
786	=item T ecb_le_to_host (T v)	993	=item T ecb_le_to_host (T v)
787		994
788	=item T ecb_host_to_be (T v)	995	=item T ecb_host_to_be (T v)
789		996
790	=item T ecb_host_to_le (T v)	997	=item T ecb_host_to_le (T v)
		998
		999	=back
791		1000
792	These functions work like their C counterparts, above, but use templates,	1001	These functions work like their C counterparts, above, but use templates,
793	which make them useful in generic code.	1002	which make them useful in generic code.
794		1003
795	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>	1004	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
…		…
798		1007
799	=head2 UNALIGNED LOAD/STORE	1008	=head2 UNALIGNED LOAD/STORE
800		1009
801	These function load or store unaligned multi-byte values.	1010	These function load or store unaligned multi-byte values.
802		1011
803	=over 4	1012	=over
804		1013
805	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)	1014	=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
806		1015
807	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)	1016	=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
808		1017
…		…
852		1061
853	=back	1062	=back
854		1063
855	In C++ the following additional template functions are supported:	1064	In C++ the following additional template functions are supported:
856		1065
857	=over 4	1066	=over
858		1067
859	=item T ecb_peek<T> (const void *ptr)	1068	=item T ecb_peek<T> (const void *ptr)
860		1069
861	=item T ecb_peek_be<T> (const void *ptr)	1070	=item T ecb_peek_be<T> (const void *ptr)
862		1071
…		…
893	=item ecb_poke_be_u (void *ptr, T v)	1102	=item ecb_poke_be_u (void *ptr, T v)
894		1103
895	=item ecb_poke_le_u (void *ptr, T v)	1104	=item ecb_poke_le_u (void *ptr, T v)
896		1105
897	Again, similarly to their C counterparts, these functions store an	1106	Again, similarly to their C counterparts, these functions store an
898	unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to	1107	unsigned 8, 16, 32 or 64 bit value to memory, with optional conversion to
899	big/little endian.	1108	big/little endian.
900		1109
901	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.	1110	C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
902		1111
903	Unlike their C counterparts, these functions support 8 bit quantities	1112	Unlike their C counterparts, these functions support 8 bit quantities
904	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),	1113	(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
905	all of which hopefully makes them more useful in generic code.	1114	all of which hopefully makes them more useful in generic code.
906		1115
907	=back	1116	=back
908		1117
		1118	=head2 FAST INTEGER TO STRING
		1119
		1120	Libecb defines a set of very fast integer to decimal string (or integer
		1121	to ASCII, short C<i2a>) functions. These work by converting the integer
		1122	to a fixed point representation and then successively multiplying out
		1123	the topmost digits. Unlike some other, also very fast, libraries, ecb's
		1124	algorithm should be completely branchless per digit, and does not rely on
		1125	the presence of special CPU functions (such as C<clz>).
		1126
		1127	There is a high level API that takes an C<int32_t>, C<uint32_t>,
		1128	C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
		1129	harder to use but supports slightly more formatting options.
		1130
		1131	=head3 HIGH LEVEL API
		1132
		1133	The high level API consists of four functions, one each for C<int32_t>,
		1134	C<uint32_t>, C<int64_t> and C<uint64_t>:
		1135
		1136	Example:
		1137
		1138	char buf[ECB_I2A_MAX_DIGITS + 1];
		1139	char *end = ecb_i2a_i32 (buf, 17262);
		1140	*end = 0;
		1141	// buf now contains "17262"
		1142
		1143	=over
		1144
		1145	=item ECB_I2A_I32_DIGITS (=11)
		1146
		1147	=item char ecb_i2a_u32 (char ptr, uint32_t value)
		1148
		1149	Takes an C<uint32_t> I<value> and formats it as a decimal number starting
		1150	at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
		1151	pointer to just after the generated string, where you would normally put
		1152	the terminating C<0> character. This function outputs the minimum number
		1153	of digits.
		1154
		1155	=item ECB_I2A_U32_DIGITS (=10)
		1156
		1157	=item char ecb_i2a_i32 (char ptr, int32_t value)
		1158
		1159	Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
		1160	sign if needed.
		1161
		1162	=item ECB_I2A_I64_DIGITS (=20)
		1163
		1164	=item char ecb_i2a_u64 (char ptr, uint64_t value)
		1165
		1166	=item ECB_I2A_U64_DIGITS (=21)
		1167
		1168	=item char ecb_i2a_i64 (char ptr, int64_t value)
		1169
		1170	Similar to their 32 bit counterparts, these take a 64 bit argument.
		1171
		1172	=item ECB_I2A_MAX_DIGITS (=21)
		1173
		1174	Instead of using a type specific length macro, you can just use
		1175	C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
		1176
		1177	=back
		1178
		1179	=head3 LOW-LEVEL API
		1180
		1181	The functions above use a number of low-level APIs which have some strict
		1182	limitations, but can be used as building blocks (studying C<ecb_i2a_i32>
		1183	and related functions is recommended).
		1184
		1185	There are three families of functions: functions that convert a number
		1186	to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
		1187	for "leading zeroes"), functions that generate up to N digits, skipping
		1188	leading zeroes (C<_N>), and functions that can generate more digits, but
		1189	the leading digit has limited range (C<_xN>).
		1190
		1191	None of the functions deal with negative numbers.
		1192
		1193	Example: convert an IP address in an C<uint32_t> into dotted-quad:
		1194
		1195	uint32_t ip = 0x0a000164; // 10.0.1.100
		1196	char ips[3 * 4 + 3 + 1];
		1197	char *ptr = ips;
		1198	ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
		1199	ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
		1200	ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
		1201	ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
		1202	printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
		1203
		1204	=over
		1205
		1206	=item char ecb_i2a_02 (char ptr, uint32_t value) // 32 bit
		1207
		1208	=item char ecb_i2a_03 (char ptr, uint32_t value) // 32 bit
		1209
		1210	=item char ecb_i2a_04 (char ptr, uint32_t value) // 32 bit
		1211
		1212	=item char ecb_i2a_05 (char ptr, uint32_t value) // 64 bit
		1213
		1214	=item char ecb_i2a_06 (char ptr, uint32_t value) // 64 bit
		1215
		1216	=item char ecb_i2a_07 (char ptr, uint32_t value) // 64 bit
		1217
		1218	=item char ecb_i2a_08 (char ptr, uint32_t value) // 64 bit
		1219
		1220	=item char ecb_i2a_09 (char ptr, uint32_t value) // 64 bit
		1221
		1222	The C<< ecb_i2a_0I<N> >> functions take an unsigned I<value> and convert
		1223	them to exactly I<N> digits, returning a pointer to the first character
		1224	after the digits. The I<value> must be in range. The functions marked with
		1225	I<32 bit> do their calculations internally in 32 bit, the ones marked with
		1226	I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
		1227	architectures (the high level API decides on 32 vs. 64 bit versions using
		1228	C<ECB_64BIT_NATIVE>).
		1229
		1230	=item char ecb_i2a_2 (char ptr, uint32_t value) // 32 bit
		1231
		1232	=item char ecb_i2a_3 (char ptr, uint32_t value) // 32 bit
		1233
		1234	=item char ecb_i2a_4 (char ptr, uint32_t value) // 32 bit
		1235
		1236	=item char ecb_i2a_5 (char ptr, uint32_t value) // 64 bit
		1237
		1238	=item char ecb_i2a_6 (char ptr, uint32_t value) // 64 bit
		1239
		1240	=item char ecb_i2a_7 (char ptr, uint32_t value) // 64 bit
		1241
		1242	=item char ecb_i2a_8 (char ptr, uint32_t value) // 64 bit
		1243
		1244	=item char ecb_i2a_9 (char ptr, uint32_t value) // 64 bit
		1245
		1246	Similarly, the C<< ecb_i2a_I<N> >> functions take an unsigned I<value>
		1247	and convert them to at most I<N> digits, suppressing leading zeroes, and
		1248	returning a pointer to the first character after the digits.
		1249
		1250	=item ECB_I2A_MAX_X5 (=59074)
		1251
		1252	=item char ecb_i2a_x5 (char ptr, uint32_t value) // 32 bit
		1253
		1254	=item ECB_I2A_MAX_X10 (=2932500665)
		1255
		1256	=item char ecb_i2a_x10 (char ptr, uint32_t value) // 64 bit
		1257
		1258	The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >>
		1259	functions, but they can generate one digit more, as long as the number
		1260	is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
		1261	16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
		1262	respectively.
		1263
		1264	For example, the digit part of a 32 bit signed integer just fits into the
		1265	C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
		1266	digit number, it can convert all 32 bit signed numbers. Sadly, it's not
		1267	good enough for 32 bit unsigned numbers.
		1268
		1269	=back
		1270
909	=head2 FLOATING POINT FIDDLING	1271	=head2 FLOATING POINT FIDDLING
910		1272
911	=over 4	1273	=over
912		1274
913	=item ECB_INFINITY [-UECB_NO_LIBM]	1275	=item ECB_INFINITY [-UECB_NO_LIBM]
914		1276
915	Evaluates to positive infinity if supported by the platform, otherwise to	1277	Evaluates to positive infinity if supported by the platform, otherwise to
916	a truly huge number.	1278	a truly huge number.
…		…
941	IEEE compliant, of course at a speed and code size penalty, and of course	1303	IEEE compliant, of course at a speed and code size penalty, and of course
942	also within reasonable limits (it tries to convert NaNs, infinities and	1304	also within reasonable limits (it tries to convert NaNs, infinities and
943	denormals, but will likely convert negative zero to positive zero).	1305	denormals, but will likely convert negative zero to positive zero).
944		1306
945	On all modern platforms (where C<ECB_STDFP> is true), the compiler should	1307	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
946	be able to optimise away this function completely.	1308	be able to completely optimise away the 32 and 64 bit functions.
947		1309
948	These functions can be helpful when serialising floats to the network - you	1310	These functions can be helpful when serialising floats to the network - you
949	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.	1311	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
950		1312
951	Another use for these functions is to manipulate floating point values	1313	Another use for these functions is to manipulate floating point values
…		…
994		1356
995	=back	1357	=back
996		1358
997	=head2 ARITHMETIC	1359	=head2 ARITHMETIC
998		1360
999	=over 4	1361	=over
1000		1362
1001	=item x = ecb_mod (m, n)	1363	=item x = ecb_mod (m, n)
1002		1364
1003	Returns C<m> modulo C<n>, which is the same as the positive remainder	1365	Returns C<m> modulo C<n>, which is the same as the positive remainder
1004	of the division operation between C<m> and C<n>, using floored	1366	of the division operation between C<m> and C<n>, using floored
…		…
1011	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be	1373	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
1012	negatable, that is, both C<m> and C<-m> must be representable in its	1374	negatable, that is, both C<m> and C<-m> must be representable in its
1013	type (this typically excludes the minimum signed integer value, the same	1375	type (this typically excludes the minimum signed integer value, the same
1014	limitation as for C</> and C<%> in C).	1376	limitation as for C</> and C<%> in C).
1015		1377
1016	Current GCC versions compile this into an efficient branchless sequence on	1378	Current GCC/clang versions compile this into an efficient branchless
1017	almost all CPUs.	1379	sequence on almost all CPUs.
1018		1380
1019	For example, when you want to rotate forward through the members of an	1381	For example, when you want to rotate forward through the members of an
1020	array for increasing C<m> (which might be negative), then you should use	1382	array for increasing C<m> (which might be negative), then you should use
1021	C<ecb_mod>, as the C<%> operator might give either negative results, or	1383	C<ecb_mod>, as the C<%> operator might give either negative results, or
1022	change direction for negative values:	1384	change direction for negative values:
…		…
1035		1397
1036	=back	1398	=back
1037		1399
1038	=head2 UTILITY	1400	=head2 UTILITY
1039		1401
1040	=over 4	1402	=over
1041		1403
1042	=item element_count = ecb_array_length (name)	1404	=item element_count = ecb_array_length (name)
1043		1405
1044	Returns the number of elements in the array C<name>. For example:	1406	Returns the number of elements in the array C<name>. For example:
1045		1407
…		…
1053		1415
1054	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF	1416	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
1055		1417
1056	These symbols need to be defined before including F<ecb.h> the first time.	1418	These symbols need to be defined before including F<ecb.h> the first time.
1057		1419
1058	=over 4	1420	=over
1059		1421
1060	=item ECB_NO_THREADS	1422	=item ECB_NO_THREADS
1061		1423
1062	If F<ecb.h> is never used from multiple threads, then this symbol can	1424	If F<ecb.h> is never used from multiple threads, then this symbol can
1063	be defined, in which case memory fences (and similar constructs) are	1425	be defined, in which case memory fences (and similar constructs) are
…		…
1067		1429
1068	=item ECB_NO_SMP	1430	=item ECB_NO_SMP
1069		1431
1070	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from	1432	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
1071	multiple threads, but never concurrently (e.g. if the system the program	1433	multiple threads, but never concurrently (e.g. if the system the program
1072	runs on has only a single CPU with a single core, no hyperthreading and so	1434	runs on has only a single CPU with a single core, no hyper-threading and so
1073	on), then this symbol can be defined, leading to more efficient code and	1435	on), then this symbol can be defined, leading to more efficient code and
1074	fewer dependencies.	1436	fewer dependencies.
1075		1437
1076	=item ECB_NO_LIBM	1438	=item ECB_NO_LIBM
1077		1439
…		…
1087	intended to be internal-use only, some of which we forgot to document, and	1449	intended to be internal-use only, some of which we forgot to document, and
1088	some of which we hide because we are not sure we will keep the interface	1450	some of which we hide because we are not sure we will keep the interface
1089	stable.	1451	stable.
1090		1452
1091	While you are welcome to rummage around and use whatever you find useful	1453	While you are welcome to rummage around and use whatever you find useful
1092	(we can't stop you), keep in mind that we will change undocumented	1454	(we don't want to stop you), keep in mind that we will change undocumented
1093	functionality in incompatible ways without thinking twice, while we are	1455	functionality in incompatible ways without thinking twice, while we are
1094	considerably more conservative with documented things.	1456	considerably more conservative with documented things.
1095		1457
1096	=head1 AUTHORS	1458	=head1 AUTHORS
1097		1459
1098	C<libecb> is designed and maintained by:	1460	C<libecb> is designed and maintained by:
1099		1461
1100	Emanuele Giaquinta <e.giaquinta@glauco.it>	1462	Emanuele Giaquinta <e.giaquinta@glauco.it>
1101	Marc Alexander Lehmann <schmorp@schmorp.de>	1463	Marc Alexander Lehmann <schmorp@schmorp.de>
1102
1103

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Comparing libecb/ecb.pod (file contents): Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC vs. Revision 1.104 by root, Fri Mar 25 08:44:14 2022 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.81 by root, Mon Jan 20 21:01:29 2020 UTC vs.
Revision 1.104 by root, Fri Mar 25 08:44:14 2022 UTC