[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 1.53 by root, Wed Dec 5 16:31:27 2012 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	which is typically true for both C and C++ compilers.
		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.
		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.
		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	=back
		156
55	=head2 GCC ATTRIBUTES	157	=head2 GCC ATTRIBUTES
56		158
57	blabla where to put, what others	159	A major part of libecb deals with GCC attributes. These are additional
		160	attributes that you can assign to functions, variables and sometimes even
		161	types - much like C<const> or C<volatile> in C.
		162
		163	While GCC allows declarations to show up in many surprising places,
		164	but not in many expected places, the safest way is to put attribute
		165	declarations before the whole declaration:
		166
		167	ecb_const int mysqrt (int a);
		168	ecb_unused int i;
		169
		170	For variables, it is often nicer to put the attribute after the name, and
		171	avoid multiple declarations using commas:
		172
		173	int i ecb_unused;
58		174
59	=over 4	175	=over 4
60		176
61	=item ecb_attribute ((attrs...))	177	=item ecb_attribute ((attrs...))
62		178
…		…
83	#else	199	#else
84	return 0;	200	return 0;
85	#endif	201	#endif
86	}	202	}
87		203
		204	=item ecb_inline
		205
		206	This is not actually an attribute, but you use it like one. It expands
		207	either to C<static inline> or to just C<static>, if inline isn't
		208	supported. It should be used to declare functions that should be inlined,
		209	for code size or speed reasons.
		210
		211	Example: inline this function, it surely will reduce codesize.
		212
		213	ecb_inline int
		214	negmul (int a, int b)
		215	{
		216	return - (a * b);
		217	}
		218
88	=item ecb_noinline	219	=item ecb_noinline
89		220
90	Prevent a function from being inlined - it might be optimised away, but	221	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	222	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.	223	is rarely called and large enough for inlining not to be helpful.
93		224
94	=item ecb_noreturn	225	=item ecb_noreturn
95		226
		227	Marks a function as "not returning, ever". Some typical functions that
		228	don't return are C<exit> or C<abort> (which really works hard to not
		229	return), and now you can make your own:
		230
		231	ecb_noreturn void
		232	my_abort (const char *errline)
		233	{
		234	puts (errline);
		235	abort ();
		236	}
		237
		238	In this case, the compiler would probably be smart enough to deduce it on
		239	its own, so this is mainly useful for declarations.
		240
		241	=item ecb_restrict
		242
		243	Expands to the C<restrict> keyword or equivalent on compilers that support
		244	them, and to nothing on others. Must be specified on a pointer type or
		245	an array index to indicate that the memory doesn't alias with any other
		246	restricted pointer in the same scope.
		247
		248	Example: multiply a vector, and allow the compiler to parallelise the
		249	loop, because it knows it doesn't overwrite input values.
		250
		251	void
		252	multiply (float *ecb_restrict src,
		253	float *ecb_restrict dst,
		254	int len, float factor)
		255	{
		256	int i;
		257
		258	for (i = 0; i < len; ++i)
		259	dst [i] = src [i] * factor;
		260	}
		261
96	=item ecb_const	262	=item ecb_const
97		263
		264	Declares that the function only depends on the values of its arguments,
		265	much like a mathematical function. It specifically does not read or write
		266	any memory any arguments might point to, global variables, or call any
		267	non-const functions. It also must not have any side effects.
		268
		269	Such a function can be optimised much more aggressively by the compiler -
		270	for example, multiple calls with the same arguments can be optimised into
		271	a single call, which wouldn't be possible if the compiler would have to
		272	expect any side effects.
		273
		274	It is best suited for functions in the sense of mathematical functions,
		275	such as a function returning the square root of its input argument.
		276
		277	Not suited would be a function that calculates the hash of some memory
		278	area you pass in, prints some messages or looks at a global variable to
		279	decide on rounding.
		280
		281	See C<ecb_pure> for a slightly less restrictive class of functions.
		282
98	=item ecb_pure	283	=item ecb_pure
99		284
		285	Similar to C<ecb_const>, declares a function that has no side
		286	effects. Unlike C<ecb_const>, the function is allowed to examine global
		287	variables and any other memory areas (such as the ones passed to it via
		288	pointers).
		289
		290	While these functions cannot be optimised as aggressively as C<ecb_const>
		291	functions, they can still be optimised away in many occasions, and the
		292	compiler has more freedom in moving calls to them around.
		293
		294	Typical examples for such functions would be C<strlen> or C<memcmp>. A
		295	function that calculates the MD5 sum of some input and updates some MD5
		296	state passed as argument would I<NOT> be pure, however, as it would modify
		297	some memory area that is not the return value.
		298
100	=item ecb_hot	299	=item ecb_hot
101		300
		301	This declares a function as "hot" with regards to the cache - the function
		302	is used so often, that it is very beneficial to keep it in the cache if
		303	possible.
		304
		305	The compiler reacts by trying to place hot functions near to each other in
		306	memory.
		307
		308	Whether a function is hot or not often depends on the whole program,
		309	and less on the function itself. C<ecb_cold> is likely more useful in
		310	practise.
		311
102	=item ecb_cold	312	=item ecb_cold
103		313
		314	The opposite of C<ecb_hot> - declares a function as "cold" with regards to
		315	the cache, or in other words, this function is not called often, or not at
		316	speed-critical times, and keeping it in the cache might be a waste of said
		317	cache.
		318
		319	In addition to placing cold functions together (or at least away from hot
		320	functions), this knowledge can be used in other ways, for example, the
		321	function will be optimised for size, as opposed to speed, and codepaths
		322	leading to calls to those functions can automatically be marked as if
		323	C<ecb_expect_false> had been used to reach them.
		324
		325	Good examples for such functions would be error reporting functions, or
		326	functions only called in exceptional or rare cases.
		327
104	=item ecb_artificial	328	=item ecb_artificial
		329
		330	Declares the function as "artificial", in this case meaning that this
		331	function is not really meant to be a function, but more like an accessor
		332	- many methods in C++ classes are mere accessor functions, and having a
		333	crash reported in such a method, or single-stepping through them, is not
		334	usually so helpful, especially when it's inlined to just a few instructions.
		335
		336	Marking them as artificial will instruct the debugger about just this,
		337	leading to happier debugging and thus happier lives.
		338
		339	Example: in some kind of smart-pointer class, mark the pointer accessor as
		340	artificial, so that the whole class acts more like a pointer and less like
		341	some C++ abstraction monster.
		342
		343	template<typename T>
		344	struct my_smart_ptr
		345	{
		346	T *value;
		347
		348	ecb_artificial
		349	operator T *()
		350	{
		351	return value;
		352	}
		353	};
105		354
106	=back	355	=back
107		356
108	=head2 OPTIMISATION HINTS	357	=head2 OPTIMISATION HINTS
109		358
…		…
141		390
142	Evaluates C<expr> and returns it. In addition, it tells the compiler that	391	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	392	the C<expr> evaluates to C<value> a lot, which can be used for static
144	branch optimisations.	393	branch optimisations.
145		394
146	Usually, you want to use the more intuitive C<ecb_likely> and	395	Usually, you want to use the more intuitive C<ecb_expect_true> and
147	C<ecb_unlikely> functions instead.	396	C<ecb_expect_false> functions instead.
148		397
		398	=item bool ecb_expect_true (cond)
		399
149	=item bool ecb_likely (cond)	400	=item bool ecb_expect_false (cond)
150
151	=item bool ecb_unlikely (cond)
152		401
153	These two functions expect a expression that is true or false and return	402	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	403	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:	404	other conditional statement, it will not change the program:
156		405
157	/* these two do the same thing */	406	/* these two do the same thing */
158	if (some_condition) ...;	407	if (some_condition) ...;
159	if (ecb_likely (some_condition)) ...;	408	if (ecb_expect_true (some_condition)) ...;
160		409
161	However, by using C<ecb_likely>, you tell the compiler that the condition	410	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	411	condition is likely to be true (and for C<ecb_expect_false>, that it is
163	true).	412	unlikely to be true).
164		413
165	For example, when you check for a null pointer and expect this to be a	414	For example, when you check for a null pointer and expect this to be a
166	rare, exceptional, case, then use C<ecb_unlikely>:	415	rare, exceptional, case, then use C<ecb_expect_false>:
167		416
168	void my_free (void *ptr)	417	void my_free (void *ptr)
169	{	418	{
170	if (ecb_unlikely (ptr == 0))	419	if (ecb_expect_false (ptr == 0))
171	return;	420	return;
172	}	421	}
173		422
174	Consequent use of these functions to mark away exceptional cases or to	423	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	424	tell the compiler what the hot path through a function is can increase
176	performance considerably.	425	performance considerably.
		426
		427	You might know these functions under the name C<likely> and C<unlikely>
		428	- while these are common aliases, we find that the expect name is easier
		429	to understand when quickly skimming code. If you wish, you can use
		430	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		431	C<ecb_expect_false> - these are simply aliases.
177		432
178	A very good example is in a function that reserves more space for some	433	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) -	434	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	435	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:	436	you expect that most checks will turn out to be false:
182		437
183	/* make sure we have "size" extra room in our buffer */	438	/* make sure we have "size" extra room in our buffer */
184	ecb_inline void	439	ecb_inline void
185	reserve (int size)	440	reserve (int size)
186	{	441	{
187	if (ecb_unlikely (current + size > end))	442	if (ecb_expect_false (current + size > end))
188	real_reserve_method (size); /* presumably noinline */	443	real_reserve_method (size); /* presumably noinline */
189	}	444	}
190		445
191	=item bool ecb_assume (cond)	446	=item bool ecb_assume (cond)
192		447
…		…
195		450
196	This can be used to teach the compiler about invariants or other	451	This can be used to teach the compiler about invariants or other
197	conditions that might improve code generation, but which are impossible to	452	conditions that might improve code generation, but which are impossible to
198	deduce form the code itself.	453	deduce form the code itself.
199		454
200	For example, the example reservation function from the C<ecb_unlikely>	455	For example, the example reservation function from the C<ecb_expect_false>
201	description could be written thus (only C<ecb_assume> was added):	456	description could be written thus (only C<ecb_assume> was added):
202		457
203	ecb_inline void	458	ecb_inline void
204	reserve (int size)	459	reserve (int size)
205	{	460	{
206	if (ecb_unlikely (current + size > end))	461	if (ecb_expect_false (current + size > end))
207	real_reserve_method (size); /* presumably noinline */	462	real_reserve_method (size); /* presumably noinline */
208		463
209	ecb_assume (current + size <= end);	464	ecb_assume (current + size <= end);
210	}	465	}
211		466
…		…
260	After processing the node, (part of) the next node might already be in	515	After processing the node, (part of) the next node might already be in
261	cache.	516	cache.
262		517
263	=back	518	=back
264		519
265	=head2 BIT FIDDLING / BITSTUFFS	520	=head2 BIT FIDDLING / BIT WIZARDRY
266		521
267	=over 4	522	=over 4
268		523
269	=item bool ecb_big_endian ()	524	=item bool ecb_big_endian ()
270		525
…		…
272		527
273	These two functions return true if the byte order is big endian	528	These two functions return true if the byte order is big endian
274	(most-significant byte first) or little endian (least-significant byte	529	(most-significant byte first) or little endian (least-significant byte
275	first) respectively.	530	first) respectively.
276		531
		532	On systems that are neither, their return values are unspecified.
		533
277	=item int ecb_ctz32 (uint32_t x)	534	=item int ecb_ctz32 (uint32_t x)
278		535
		536	=item int ecb_ctz64 (uint64_t x)
		537
279	Returns the index of the least significant bit set in C<x> (or	538	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	539	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	540	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.,	541
283	floor(log2(n)). For example:	542	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		543
		544	For example:
284		545
285	ecb_ctz32 (3) = 0	546	ecb_ctz32 (3) = 0
286	ecb_ctz32 (6) = 1	547	ecb_ctz32 (6) = 1
287		548
		549	=item bool ecb_is_pot32 (uint32_t x)
		550
		551	=item bool ecb_is_pot64 (uint32_t x)
		552
		553	Return true iff C<x> is a power of two or C<x == 0>.
		554
		555	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		556
		557	=item int ecb_ld32 (uint32_t x)
		558
		559	=item int ecb_ld64 (uint64_t x)
		560
		561	Returns the index of the most significant bit set in C<x>, or the number
		562	of digits the number requires in binary (so that C<< 2**ld <= x <
		563	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		564	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		565	example to see how many bits a certain number requires to be encoded.
		566
		567	This function is similar to the "count leading zero bits" function, except
		568	that that one returns how many zero bits are "in front" of the number (in
		569	the given data type), while C<ecb_ld> returns how many bits the number
		570	itself requires.
		571
		572	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		573
288	=item int ecb_popcount32 (uint32_t x)	574	=item int ecb_popcount32 (uint32_t x)
289		575
		576	=item int ecb_popcount64 (uint64_t x)
		577
290	Returns the number of bits set to 1 in C<x>. For example:	578	Returns the number of bits set to 1 in C<x>.
		579
		580	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		581
		582	For example:
291		583
292	ecb_popcount32 (7) = 3	584	ecb_popcount32 (7) = 3
293	ecb_popcount32 (255) = 8	585	ecb_popcount32 (255) = 8
294		586
		587	=item uint8_t ecb_bitrev8 (uint8_t x)
		588
		589	=item uint16_t ecb_bitrev16 (uint16_t x)
		590
		591	=item uint32_t ecb_bitrev32 (uint32_t x)
		592
		593	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		594	and so on.
		595
		596	Example:
		597
		598	ecb_bitrev8 (0xa7) = 0xea
		599	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		600
295	=item uint32_t ecb_bswap16 (uint32_t x)	601	=item uint32_t ecb_bswap16 (uint32_t x)
296		602
297	=item uint32_t ecb_bswap32 (uint32_t x)	603	=item uint32_t ecb_bswap32 (uint32_t x)
298		604
		605	=item uint64_t ecb_bswap64 (uint64_t x)
		606
299	These two functions return the value of the 16-bit (32-bit) variable	607	These functions return the value of the 16-bit (32-bit, 64-bit) value
300	C<x> after reversing the order of bytes.	608	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		609	C<ecb_bswap32>).
		610
		611	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		612
		613	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		614
		615	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		616
		617	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		618
		619	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		620
		621	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
301		622
302	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	623	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
303		624
304	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	625	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
305		626
306	These two functions return the value of C<x> after shifting all the bits	627	These two families of functions return the value of C<x> after rotating
307	by C<count> positions to the right or left respectively.	628	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		629	(C<ecb_rotl>).
		630
		631	Current GCC versions understand these functions and usually compile them
		632	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		633	x86).
308		634
309	=back	635	=back
310		636
		637	=head2 FLOATING POINT FIDDLING
		638
		639	=over 4
		640
		641	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		642
		643	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		644
		645	These functions each take an argument in the native C<float> or C<double>
		646	type and return the IEEE 754 bit representation of it.
		647
		648	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		649	will be the most significant bit, followed by exponent and mantissa.
		650
		651	This function should work even when the native floating point format isn't
		652	IEEE compliant, of course at a speed and code size penalty, and of course
		653	also within reasonable limits (it tries to convert NaNs, infinities and
		654	denormals, but will likely convert negative zero to positive zero).
		655
		656	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		657	be able to optimise away this function completely.
		658
		659	These functions can be helpful when serialising floats to the network - you
		660	can serialise the return value like a normal uint32_t/uint64_t.
		661
		662	Another use for these functions is to manipulate floating point values
		663	directly.
		664
		665	Silly example: toggle the sign bit of a float.
		666
		667	/* On gcc-4.7 on amd64, */
		668	/* this results in a single add instruction to toggle the bit, and 4 extra */
		669	/* instructions to move the float value to an integer register and back. */
		670
		671	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		672
		673	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		674
		675	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		676
		677	The reverse operation of the previos function - takes the bit representation
		678	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		679	or C<double> format.
		680
		681	This function should work even when the native floating point format isn't
		682	IEEE compliant, of course at a speed and code size penalty, and of course
		683	also within reasonable limits (it tries to convert normals and denormals,
		684	and might be lucky for infinities, and with extraordinary luck, also for
		685	negative zero).
		686
		687	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		688	be able to optimise away this function completely.
		689
		690	=back
		691
311	=head2 ARITHMETIC	692	=head2 ARITHMETIC
312		693
313	=over 4	694	=over 4
314		695
315	=item x = ecb_mod (m, n)	696	=item x = ecb_mod (m, n)
316		697
317	Returns the positive remainder of the modulo operation between C<m> and	698	Returns C<m> modulo C<n>, which is the same as the positive remainder
		699	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	700	division. Unlike the C remainder operator C<%>, this function ensures that
319	return value is always positive).	701	the return value is always positive and that the two numbers I<m> and
		702	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		703	C<ecb_mod> implements the mathematical modulo operation, which is missing
		704	in the language.
320		705
321	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	706	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	707	negatable, that is, both C<m> and C<-m> must be representable in its
323	type.	708	type (this typically excludes the minimum signed integer value, the same
		709	limitation as for C</> and C<%> in C).
		710
		711	Current GCC versions compile this into an efficient branchless sequence on
		712	almost all CPUs.
		713
		714	For example, when you want to rotate forward through the members of an
		715	array for increasing C<m> (which might be negative), then you should use
		716	C<ecb_mod>, as the C<%> operator might give either negative results, or
		717	change direction for negative values:
		718
		719	for (m = -100; m <= 100; ++m)
		720	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		721
		722	=item x = ecb_div_rd (val, div)
		723
		724	=item x = ecb_div_ru (val, div)
		725
		726	Returns C<val> divided by C<div> rounded down or up, respectively.
		727	C<val> and C<div> must have integer types and C<div> must be strictly
		728	positive. Note that these functions are implemented with macros in C
		729	and with function templates in C++.
324		730
325	=back	731	=back
326		732
327	=head2 UTILITY	733	=head2 UTILITY
328		734
329	=over 4	735	=over 4
330		736
331	=item element_count = ecb_array_length (name) [MACRO]	737	=item element_count = ecb_array_length (name)
332		738
333	Returns the number of elements in the array C<name>. For example:	739	Returns the number of elements in the array C<name>. For example:
334		740
335	int primes[] = { 2, 3, 5, 7, 11 };	741	int primes[] = { 2, 3, 5, 7, 11 };
336	int sum = 0;	742	int sum = 0;
…		…
338	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
339	sum += primes [i];	745	sum += primes [i];
340		746
341	=back	747	=back
342		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
343		750
		751	These symbols need to be defined before including F<ecb.h> the first time.
		752
		753	=over 4
		754
		755	=item ECB_NO_THREADS
		756
		757	If F<ecb.h> is never used from multiple threads, then this symbol can
		758	be defined, in which case memory fences (and similar constructs) are
		759	completely removed, leading to more efficient code and fewer dependencies.
		760
		761	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		762
		763	=item ECB_NO_SMP
		764
		765	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		766	multiple threads, but never concurrently (e.g. if the system the program
		767	runs on has only a single CPU with a single core, no hyperthreading and so
		768	on), then this symbol can be defined, leading to more efficient code and
		769	fewer dependencies.
		770
		771	=item ECB_NO_LIBM
		772
		773	When defined to C<1>, do not export any functions that might introduce
		774	dependencies on the math library (usually called F<-lm>) - these are
		775	marked with [-UECB_NO_LIBM].
		776
		777	=back
		778
		779

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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 1.53 by root, Wed Dec 5 16:31:27 2012 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 1.53 by root, Wed Dec 5 16:31:27 2012 UTC