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

Comparing libecb/ecb.pod (file contents):
Revision 1.16 by sf-exg, Thu May 26 23:32:41 2011 UTC vs.
Revision 1.55 by root, Thu Jan 9 05:16:12 2014 UTC

…		…
14		14
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around GCC built-ins, together
16	with replacement functions for other compilers. In addition to this,	16	with replacement functions for other compilers. In addition to this,
17	it provides a number of other lowlevel C utilities, such as endianness	17	it provides a number of other lowlevel C utilities, such as endianness
18	detection, byte swapping or bit rotations.	18	detection, byte swapping or bit rotations.
		19
		20	Or in other words, things that should be built into any standard C system,
		21	but aren't, implemented as efficient as possible with GCC, and still
		22	correct with other compilers.
19		23
20	More might come.	24	More might come.
21		25
22	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
23		27
…		…
50	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
51	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
52	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
53	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
54		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_t int16_t uint16_t
		64	int32_t uint32_t int64_t uint64_t
		65	intptr_t uintptr_t
		66
		67	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
		68	platform (currently C<4> or C<8>) and can be used in preprocessor
		69	expressions.
		70
		71	For C<ptrdiff_t> and C<size_t> use C<stddef.h>.
		72
		73	=head2 LANGUAGE/COMPILER VERSIONS
		74
		75	All the following symbols expand to an expression that can be tested in
		76	preprocessor instructions as well as treated as a boolean (use C<!!> to
		77	ensure it's either C<0> or C<1> if you need that).
		78
		79	=over 4
		80
		81	=item ECB_C
		82
		83	True if the implementation defines the C<__STDC__> macro to a true value,
		84	while not claiming to be C++.
		85
		86	=item ECB_C99
		87
		88	True if the implementation claims to be compliant to C99 (ISO/IEC
		89	9899:1999) or any later version, while not claiming to be C++.
		90
		91	Note that later versions (ECB_C11) remove core features again (for
		92	example, variable length arrays).
		93
		94	=item ECB_C11
		95
		96	True if the implementation claims to be compliant to C11 (ISO/IEC
		97	9899:2011) or any later version, while not claiming to be C++.
		98
		99	=item ECB_CPP
		100
		101	True if the implementation defines the C<__cplusplus__> macro to a true
		102	value, which is typically true for C++ compilers.
		103
		104	=item ECB_CPP11
		105
		106	True if the implementation claims to be compliant to ISO/IEC 14882:2011
		107	(C++11) or any later version.
		108
		109	=item ECB_GCC_VERSION(major,minor)
		110
		111	Expands to a true value (suitable for testing in by the preprocessor)
		112	if the compiler used is GNU C and the version is the given version, or
		113	higher.
		114
		115	This macro tries to return false on compilers that claim to be GCC
		116	compatible but aren't.
		117
		118	=item ECB_EXTERN_C
		119
		120	Expands to C<extern "C"> in C++, and a simple C<extern> in C.
		121
		122	This can be used to declare a single external C function:
		123
		124	ECB_EXTERN_C int printf (const char *format, ...);
		125
		126	=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
		127
		128	These two macros can be used to wrap multiple C<extern "C"> definitions -
		129	they expand to nothing in C.
		130
		131	They are most useful in header files:
		132
		133	ECB_EXTERN_C_BEG
		134
		135	int mycfun1 (int x);
		136	int mycfun2 (int x);
		137
		138	ECB_EXTERN_C_END
		139
		140	=item ECB_STDFP
		141
		142	If this evaluates to a true value (suitable for testing in by the
		143	preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
		144	and double/binary64 representations internally I<and> the endianness of
		145	both types match the endianness of C<uint32_t> and C<uint64_t>.
		146
		147	This means you can just copy the bits of a C<float> (or C<double>) to an
		148	C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
		149	without having to think about format or endianness.
		150
		151	This is true for basically all modern platforms, although F<ecb.h> might
		152	not be able to deduce this correctly everywhere and might err on the safe
		153	side.
		154
		155	=item ECB_AMD64, ECB_AMD64_X32
		156
		157	These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
		158	ABI, respectively, and undefined elsewhere.
		159
		160	The designers of the new X32 ABI for some inexplicable reason decided to
		161	make it look exactly like amd64, even though it's completely incompatible
		162	to that ABI, breaking about every piece of software that assumed that
		163	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
		164	necessary.
		165
		166	=back
		167
55	=head2 GCC ATTRIBUTES	168	=head2 GCC ATTRIBUTES
56		169
57	blabla where to put, what others	170	A major part of libecb deals with GCC attributes. These are additional
		171	attributes that you can assign to functions, variables and sometimes even
		172	types - much like C<const> or C<volatile> in C.
		173
		174	While GCC allows declarations to show up in many surprising places,
		175	but not in many expected places, the safest way is to put attribute
		176	declarations before the whole declaration:
		177
		178	ecb_const int mysqrt (int a);
		179	ecb_unused int i;
		180
		181	For variables, it is often nicer to put the attribute after the name, and
		182	avoid multiple declarations using commas:
		183
		184	int i ecb_unused;
58		185
59	=over 4	186	=over 4
60		187
61	=item ecb_attribute ((attrs...))	188	=item ecb_attribute ((attrs...))
62		189
…		…
83	#else	210	#else
84	return 0;	211	return 0;
85	#endif	212	#endif
86	}	213	}
87		214
		215	=item ecb_inline
		216
		217	This is not actually an attribute, but you use it like one. It expands
		218	either to C<static inline> or to just C<static>, if inline isn't
		219	supported. It should be used to declare functions that should be inlined,
		220	for code size or speed reasons.
		221
		222	Example: inline this function, it surely will reduce codesize.
		223
		224	ecb_inline int
		225	negmul (int a, int b)
		226	{
		227	return - (a * b);
		228	}
		229
88	=item ecb_noinline	230	=item ecb_noinline
89		231
90	Prevent a function from being inlined - it might be optimised away, but	232	Prevent a function from being inlined - it might be optimised away, but
91	not inlined into other functions. This is useful if you know your function	233	not inlined into other functions. This is useful if you know your function
92	is rarely called and large enough for inlining not to be helpful.	234	is rarely called and large enough for inlining not to be helpful.
93		235
94	=item ecb_noreturn	236	=item ecb_noreturn
95		237
		238	Marks a function as "not returning, ever". Some typical functions that
		239	don't return are C<exit> or C<abort> (which really works hard to not
		240	return), and now you can make your own:
		241
		242	ecb_noreturn void
		243	my_abort (const char *errline)
		244	{
		245	puts (errline);
		246	abort ();
		247	}
		248
		249	In this case, the compiler would probably be smart enough to deduce it on
		250	its own, so this is mainly useful for declarations.
		251
		252	=item ecb_restrict
		253
		254	Expands to the C<restrict> keyword or equivalent on compilers that support
		255	them, and to nothing on others. Must be specified on a pointer type or
		256	an array index to indicate that the memory doesn't alias with any other
		257	restricted pointer in the same scope.
		258
		259	Example: multiply a vector, and allow the compiler to parallelise the
		260	loop, because it knows it doesn't overwrite input values.
		261
		262	void
		263	multiply (float *ecb_restrict src,
		264	float *ecb_restrict dst,
		265	int len, float factor)
		266	{
		267	int i;
		268
		269	for (i = 0; i < len; ++i)
		270	dst [i] = src [i] * factor;
		271	}
		272
96	=item ecb_const	273	=item ecb_const
97		274
		275	Declares that the function only depends on the values of its arguments,
		276	much like a mathematical function. It specifically does not read or write
		277	any memory any arguments might point to, global variables, or call any
		278	non-const functions. It also must not have any side effects.
		279
		280	Such a function can be optimised much more aggressively by the compiler -
		281	for example, multiple calls with the same arguments can be optimised into
		282	a single call, which wouldn't be possible if the compiler would have to
		283	expect any side effects.
		284
		285	It is best suited for functions in the sense of mathematical functions,
		286	such as a function returning the square root of its input argument.
		287
		288	Not suited would be a function that calculates the hash of some memory
		289	area you pass in, prints some messages or looks at a global variable to
		290	decide on rounding.
		291
		292	See C<ecb_pure> for a slightly less restrictive class of functions.
		293
98	=item ecb_pure	294	=item ecb_pure
99		295
		296	Similar to C<ecb_const>, declares a function that has no side
		297	effects. Unlike C<ecb_const>, the function is allowed to examine global
		298	variables and any other memory areas (such as the ones passed to it via
		299	pointers).
		300
		301	While these functions cannot be optimised as aggressively as C<ecb_const>
		302	functions, they can still be optimised away in many occasions, and the
		303	compiler has more freedom in moving calls to them around.
		304
		305	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		306	function that calculates the MD5 sum of some input and updates some MD5
		307	state passed as argument would I<NOT> be pure, however, as it would modify
		308	some memory area that is not the return value.
		309
100	=item ecb_hot	310	=item ecb_hot
101		311
		312	This declares a function as "hot" with regards to the cache - the function
		313	is used so often, that it is very beneficial to keep it in the cache if
		314	possible.
		315
		316	The compiler reacts by trying to place hot functions near to each other in
		317	memory.
		318
		319	Whether a function is hot or not often depends on the whole program,
		320	and less on the function itself. C<ecb_cold> is likely more useful in
		321	practise.
		322
102	=item ecb_cold	323	=item ecb_cold
103		324
		325	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		326	the cache, or in other words, this function is not called often, or not at
		327	speed-critical times, and keeping it in the cache might be a waste of said
		328	cache.
		329
		330	In addition to placing cold functions together (or at least away from hot
		331	functions), this knowledge can be used in other ways, for example, the
		332	function will be optimised for size, as opposed to speed, and codepaths
		333	leading to calls to those functions can automatically be marked as if
		334	C<ecb_expect_false> had been used to reach them.
		335
		336	Good examples for such functions would be error reporting functions, or
		337	functions only called in exceptional or rare cases.
		338
104	=item ecb_artificial	339	=item ecb_artificial
		340
		341	Declares the function as "artificial", in this case meaning that this
		342	function is not really meant to be a function, but more like an accessor
		343	- many methods in C++ classes are mere accessor functions, and having a
		344	crash reported in such a method, or single-stepping through them, is not
		345	usually so helpful, especially when it's inlined to just a few instructions.
		346
		347	Marking them as artificial will instruct the debugger about just this,
		348	leading to happier debugging and thus happier lives.
		349
		350	Example: in some kind of smart-pointer class, mark the pointer accessor as
		351	artificial, so that the whole class acts more like a pointer and less like
		352	some C++ abstraction monster.
		353
		354	template<typename T>
		355	struct my_smart_ptr
		356	{
		357	T *value;
		358
		359	ecb_artificial
		360	operator T *()
		361	{
		362	return value;
		363	}
		364	};
105		365
106	=back	366	=back
107		367
108	=head2 OPTIMISATION HINTS	368	=head2 OPTIMISATION HINTS
109		369
…		…
141		401
142	Evaluates C<expr> and returns it. In addition, it tells the compiler that	402	Evaluates C<expr> and returns it. In addition, it tells the compiler that
143	the C<expr> evaluates to C<value> a lot, which can be used for static	403	the C<expr> evaluates to C<value> a lot, which can be used for static
144	branch optimisations.	404	branch optimisations.
145		405
146	Usually, you want to use the more intuitive C<ecb_likely> and	406	Usually, you want to use the more intuitive C<ecb_expect_true> and
147	C<ecb_unlikely> functions instead.	407	C<ecb_expect_false> functions instead.
148		408
		409	=item bool ecb_expect_true (cond)
		410
149	=item bool ecb_likely (cond)	411	=item bool ecb_expect_false (cond)
150
151	=item bool ecb_unlikely (cond)
152		412
153	These two functions expect a expression that is true or false and return	413	These two functions expect a expression that is true or false and return
154	C<1> or C<0>, respectively, so when used in the condition of an C<if> or	414	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
155	other conditional statement, it will not change the program:	415	other conditional statement, it will not change the program:
156		416
157	/* these two do the same thing */	417	/* these two do the same thing */
158	if (some_condition) ...;	418	if (some_condition) ...;
159	if (ecb_likely (some_condition)) ...;	419	if (ecb_expect_true (some_condition)) ...;
160		420
161	However, by using C<ecb_likely>, you tell the compiler that the condition	421	However, by using C<ecb_expect_true>, you tell the compiler that the
162	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be	422	condition is likely to be true (and for C<ecb_expect_false>, that it is
163	true).	423	unlikely to be true).
164		424
165	For example, when you check for a null pointer and expect this to be a	425	For example, when you check for a null pointer and expect this to be a
166	rare, exceptional, case, then use C<ecb_unlikely>:	426	rare, exceptional, case, then use C<ecb_expect_false>:
167		427
168	void my_free (void *ptr)	428	void my_free (void *ptr)
169	{	429	{
170	if (ecb_unlikely (ptr == 0))	430	if (ecb_expect_false (ptr == 0))
171	return;	431	return;
172	}	432	}
173		433
174	Consequent use of these functions to mark away exceptional cases or to	434	Consequent use of these functions to mark away exceptional cases or to
175	tell the compiler what the hot path through a function is can increase	435	tell the compiler what the hot path through a function is can increase
176	performance considerably.	436	performance considerably.
		437
		438	You might know these functions under the name C<likely> and C<unlikely>
		439	- while these are common aliases, we find that the expect name is easier
		440	to understand when quickly skimming code. If you wish, you can use
		441	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		442	C<ecb_expect_false> - these are simply aliases.
177		443
178	A very good example is in a function that reserves more space for some	444	A very good example is in a function that reserves more space for some
179	memory block (for example, inside an implementation of a string stream) -	445	memory block (for example, inside an implementation of a string stream) -
180	each time something is added, you have to check for a buffer overrun, but	446	each time something is added, you have to check for a buffer overrun, but
181	you expect that most checks will turn out to be false:	447	you expect that most checks will turn out to be false:
182		448
183	/* make sure we have "size" extra room in our buffer */	449	/* make sure we have "size" extra room in our buffer */
184	ecb_inline void	450	ecb_inline void
185	reserve (int size)	451	reserve (int size)
186	{	452	{
187	if (ecb_unlikely (current + size > end))	453	if (ecb_expect_false (current + size > end))
188	real_reserve_method (size); /* presumably noinline */	454	real_reserve_method (size); /* presumably noinline */
189	}	455	}
190		456
191	=item bool ecb_assume (cond)	457	=item bool ecb_assume (cond)
192		458
…		…
195		461
196	This can be used to teach the compiler about invariants or other	462	This can be used to teach the compiler about invariants or other
197	conditions that might improve code generation, but which are impossible to	463	conditions that might improve code generation, but which are impossible to
198	deduce form the code itself.	464	deduce form the code itself.
199		465
200	For example, the example reservation function from the C<ecb_unlikely>	466	For example, the example reservation function from the C<ecb_expect_false>
201	description could be written thus (only C<ecb_assume> was added):	467	description could be written thus (only C<ecb_assume> was added):
202		468
203	ecb_inline void	469	ecb_inline void
204	reserve (int size)	470	reserve (int size)
205	{	471	{
206	if (ecb_unlikely (current + size > end))	472	if (ecb_expect_false (current + size > end))
207	real_reserve_method (size); /* presumably noinline */	473	real_reserve_method (size); /* presumably noinline */
208		474
209	ecb_assume (current + size <= end);	475	ecb_assume (current + size <= end);
210	}	476	}
211		477
…		…
260	After processing the node, (part of) the next node might already be in	526	After processing the node, (part of) the next node might already be in
261	cache.	527	cache.
262		528
263	=back	529	=back
264		530
265	=head2 BIT FIDDLING / BITSTUFFS	531	=head2 BIT FIDDLING / BIT WIZARDRY
266		532
267	=over 4	533	=over 4
268		534
269	=item bool ecb_big_endian ()	535	=item bool ecb_big_endian ()
270		536
…		…
272		538
273	These two functions return true if the byte order is big endian	539	These two functions return true if the byte order is big endian
274	(most-significant byte first) or little endian (least-significant byte	540	(most-significant byte first) or little endian (least-significant byte
275	first) respectively.	541	first) respectively.
276		542
		543	On systems that are neither, their return values are unspecified.
		544
277	=item int ecb_ctz32 (uint32_t x)	545	=item int ecb_ctz32 (uint32_t x)
278		546
		547	=item int ecb_ctz64 (uint64_t x)
		548
279	Returns the index of the least significant bit set in C<x> (or	549	Returns the index of the least significant bit set in C<x> (or
280	equivalently the number of bits set to 0 before the least significant	550	equivalently the number of bits set to 0 before the least significant bit
281	bit set), starting from 0. If C<x> is 0 the result is undefined. A	551	set), starting from 0. If C<x> is 0 the result is undefined.
282	common use case is to compute the integer binary logarithm, i.e.,	552
283	floor(log2(n)). For example:	553	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		554
		555	For example:
284		556
285	ecb_ctz32 (3) = 0	557	ecb_ctz32 (3) = 0
286	ecb_ctz32 (6) = 1	558	ecb_ctz32 (6) = 1
287		559
		560	=item bool ecb_is_pot32 (uint32_t x)
		561
		562	=item bool ecb_is_pot64 (uint32_t x)
		563
		564	Return true iff C<x> is a power of two or C<x == 0>.
		565
		566	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		567
		568	=item int ecb_ld32 (uint32_t x)
		569
		570	=item int ecb_ld64 (uint64_t x)
		571
		572	Returns the index of the most significant bit set in C<x>, or the number
		573	of digits the number requires in binary (so that C<< 2**ld <= x <
		574	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		575	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		576	example to see how many bits a certain number requires to be encoded.
		577
		578	This function is similar to the "count leading zero bits" function, except
		579	that that one returns how many zero bits are "in front" of the number (in
		580	the given data type), while C<ecb_ld> returns how many bits the number
		581	itself requires.
		582
		583	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		584
288	=item int ecb_popcount32 (uint32_t x)	585	=item int ecb_popcount32 (uint32_t x)
289		586
		587	=item int ecb_popcount64 (uint64_t x)
		588
290	Returns the number of bits set to 1 in C<x>. For example:	589	Returns the number of bits set to 1 in C<x>.
		590
		591	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		592
		593	For example:
291		594
292	ecb_popcount32 (7) = 3	595	ecb_popcount32 (7) = 3
293	ecb_popcount32 (255) = 8	596	ecb_popcount32 (255) = 8
294		597
		598	=item uint8_t ecb_bitrev8 (uint8_t x)
		599
		600	=item uint16_t ecb_bitrev16 (uint16_t x)
		601
		602	=item uint32_t ecb_bitrev32 (uint32_t x)
		603
		604	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		605	and so on.
		606
		607	Example:
		608
		609	ecb_bitrev8 (0xa7) = 0xea
		610	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		611
295	=item uint32_t ecb_bswap16 (uint32_t x)	612	=item uint32_t ecb_bswap16 (uint32_t x)
296		613
297	=item uint32_t ecb_bswap32 (uint32_t x)	614	=item uint32_t ecb_bswap32 (uint32_t x)
298		615
		616	=item uint64_t ecb_bswap64 (uint64_t x)
		617
299	These two functions return the value of the 16-bit (32-bit) variable	618	These functions return the value of the 16-bit (32-bit, 64-bit) value
300	C<x> after reversing the order of bytes.	619	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		620	C<ecb_bswap32>).
		621
		622	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		623
		624	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		625
		626	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		627
		628	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		629
		630	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		631
		632	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
301		633
302	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	634	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
303		635
304	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	636	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
305		637
306	These two functions return the value of C<x> after shifting all the bits	638	These two families of functions return the value of C<x> after rotating
307	by C<count> positions to the right or left respectively.	639	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		640	(C<ecb_rotl>).
		641
		642	Current GCC versions understand these functions and usually compile them
		643	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		644	x86).
308		645
309	=back	646	=back
310		647
		648	=head2 FLOATING POINT FIDDLING
		649
		650	=over 4
		651
		652	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		653
		654	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		655
		656	These functions each take an argument in the native C<float> or C<double>
		657	type and return the IEEE 754 bit representation of it.
		658
		659	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		660	will be the most significant bit, followed by exponent and mantissa.
		661
		662	This function should work even when the native floating point format isn't
		663	IEEE compliant, of course at a speed and code size penalty, and of course
		664	also within reasonable limits (it tries to convert NaNs, infinities and
		665	denormals, but will likely convert negative zero to positive zero).
		666
		667	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		668	be able to optimise away this function completely.
		669
		670	These functions can be helpful when serialising floats to the network - you
		671	can serialise the return value like a normal uint32_t/uint64_t.
		672
		673	Another use for these functions is to manipulate floating point values
		674	directly.
		675
		676	Silly example: toggle the sign bit of a float.
		677
		678	/* On gcc-4.7 on amd64, */
		679	/* this results in a single add instruction to toggle the bit, and 4 extra */
		680	/* instructions to move the float value to an integer register and back. */
		681
		682	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		683
		684	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		685
		686	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		687
		688	The reverse operation of the previos function - takes the bit representation
		689	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		690	or C<double> format.
		691
		692	This function should work even when the native floating point format isn't
		693	IEEE compliant, of course at a speed and code size penalty, and of course
		694	also within reasonable limits (it tries to convert normals and denormals,
		695	and might be lucky for infinities, and with extraordinary luck, also for
		696	negative zero).
		697
		698	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		699	be able to optimise away this function completely.
		700
		701	=back
		702
311	=head2 ARITHMETIC	703	=head2 ARITHMETIC
312		704
313	=over 4	705	=over 4
314		706
315	=item x = ecb_mod (m, n)	707	=item x = ecb_mod (m, n)
316		708
317	Returns the positive remainder of the modulo operation between C<m> and	709	Returns C<m> modulo C<n>, which is the same as the positive remainder
		710	of the division operation between C<m> and C<n>, using floored
318	C<n>. Unlike the C modulo operator C<%>, this function ensures that the	711	division. Unlike the C remainder operator C<%>, this function ensures that
319	return value is always positive).	712	the return value is always positive and that the two numbers I<m> and
		713	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		714	C<ecb_mod> implements the mathematical modulo operation, which is missing
		715	in the language.
320		716
321	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	717	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
322	negatable, that is, both C<m> and C<-m> must be representable in its	718	negatable, that is, both C<m> and C<-m> must be representable in its
323	type.	719	type (this typically excludes the minimum signed integer value, the same
		720	limitation as for C</> and C<%> in C).
		721
		722	Current GCC versions compile this into an efficient branchless sequence on
		723	almost all CPUs.
		724
		725	For example, when you want to rotate forward through the members of an
		726	array for increasing C<m> (which might be negative), then you should use
		727	C<ecb_mod>, as the C<%> operator might give either negative results, or
		728	change direction for negative values:
		729
		730	for (m = -100; m <= 100; ++m)
		731	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		732
		733	=item x = ecb_div_rd (val, div)
		734
		735	=item x = ecb_div_ru (val, div)
		736
		737	Returns C<val> divided by C<div> rounded down or up, respectively.
		738	C<val> and C<div> must have integer types and C<div> must be strictly
		739	positive. Note that these functions are implemented with macros in C
		740	and with function templates in C++.
324		741
325	=back	742	=back
326		743
327	=head2 UTILITY	744	=head2 UTILITY
328		745
329	=over 4	746	=over 4
330		747
331	=item element_count = ecb_array_length (name) [MACRO]	748	=item element_count = ecb_array_length (name)
332		749
333	Returns the number of elements in the array C<name>. For example:	750	Returns the number of elements in the array C<name>. For example:
334		751
335	int primes[] = { 2, 3, 5, 7, 11 };	752	int primes[] = { 2, 3, 5, 7, 11 };
336	int sum = 0;	753	int sum = 0;
…		…
338	for (i = 0; i < ecb_array_length (primes); i++)	755	for (i = 0; i < ecb_array_length (primes); i++)
339	sum += primes [i];	756	sum += primes [i];
340		757
341	=back	758	=back
342		759
		760	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
343		761
		762	These symbols need to be defined before including F<ecb.h> the first time.
		763
		764	=over 4
		765
		766	=item ECB_NO_THREADS
		767
		768	If F<ecb.h> is never used from multiple threads, then this symbol can
		769	be defined, in which case memory fences (and similar constructs) are
		770	completely removed, leading to more efficient code and fewer dependencies.
		771
		772	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		773
		774	=item ECB_NO_SMP
		775
		776	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		777	multiple threads, but never concurrently (e.g. if the system the program
		778	runs on has only a single CPU with a single core, no hyperthreading and so
		779	on), then this symbol can be defined, leading to more efficient code and
		780	fewer dependencies.
		781
		782	=item ECB_NO_LIBM
		783
		784	When defined to C<1>, do not export any functions that might introduce
		785	dependencies on the math library (usually called F<-lm>) - these are
		786	marked with [-UECB_NO_LIBM].
		787
		788	=back
		789
		790

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Comparing libecb/ecb.pod (file contents): Revision 1.16 by sf-exg, Thu May 26 23:32:41 2011 UTC vs. Revision 1.55 by root, Thu Jan 9 05:16:12 2014 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.16 by sf-exg, Thu May 26 23:32:41 2011 UTC vs.
Revision 1.55 by root, Thu Jan 9 05:16:12 2014 UTC