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

Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.7 by root, Thu May 26 20:49:40 2011 UTC vs.
Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC

…		…
		1	=head1 LIBECB - e-C-Builtins
		2
1	=head1 LIBECB	3	=head2 ABOUT LIBECB
2		4
3	You suck, we don't(tm)	5	Libecb is currently a simple header file that doesn't require any
		6	configuration to use or include in your project.
		7
		8	It's part of the e-suite of libraries, other memembers of which include
		9	libev and libeio.
		10
		11	Its homepage can be found here:
		12
		13	http://software.schmorp.de/pkg/libecb
		14
		15	It mainly provides a number of wrappers around GCC built-ins, together
		16	with replacement functions for other compilers. In addition to this,
		17	it provides a number of other lowlevel C utilities, such endienness
		18	detection, byte swapping or bit rotations.
		19
		20	More might come.
4		21
5	=head2 ABOUT THE HEADER	22	=head2 ABOUT THE HEADER
6		23
7	- how to include it	24	At the moment, all you have to do is copy F<ecb.h> somewhere where your
8	- it includes inttypes.h	25	compiler can find it and include it:
9	- no .a	26
10	- whats a bool	27	#include <ecb.h>
11	- function mean macro or function	28
12	- macro means untyped	29	The header should work fine for both C and C++ compilation, and gives you
		30	all of F<inttypes.h> in addition to the ECB symbols.
		31
		32	There are currently no objetc files to link to - future versions might
		33	come with an (optional) object code library to link against, to reduce
		34	code size or gain access to additional features.
		35
		36	It also currently includes everything from F<inttypes.h>.
		37
		38	=head2 ABOUT THIS MANUAL / CONVENTIONS
		39
		40	This manual mainly describes each (public) function available after
		41	including the F<ecb.h> header. The header might define other symbols than
		42	these, but these are not part of the public API, and not supported in any
		43	way.
		44
		45	When the manual mentions a "function" then this could be defined either as
		46	as inline function, a macro, or an external symbol.
		47
		48	When functions use a concrete standard type, such as C<int> or
		49	C<uint32_t>, then the corresponding function works only with that type. If
		50	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
		52	is usually implemented as a macro. Specifically, a "bool" in this manual
		53	refers to any kind of boolean value, not a specific type.
13		54
14	=head2 GCC ATTRIBUTES	55	=head2 GCC ATTRIBUTES
15		56
16	blabla where to put, what others	57	blabla where to put, what others
17		58
39	#endif	80	#endif
40	}	81	}
41		82
42	=item ecb_noinline	83	=item ecb_noinline
43		84
44	Prevent a function from being inlined - it might be optimsied away, but	85	Prevent a function from being inlined - it might be optimised away, but
45	not inlined into other functions. This is useful if you know your function	86	not inlined into other functions. This is useful if you know your function
46	is rarely called and large enough for inlining not to be helpful.	87	is rarely called and large enough for inlining not to be helpful.
47		88
48	=item ecb_noreturn	89	=item ecb_noreturn
49		90
…		…
111	/* these two do the same thing */	152	/* these two do the same thing */
112	if (some_condition) ...;	153	if (some_condition) ...;
113	if (ecb_likely (some_condition)) ...;	154	if (ecb_likely (some_condition)) ...;
114		155
115	However, by using C<ecb_likely>, you tell the compiler that the condition	156	However, by using C<ecb_likely>, you tell the compiler that the condition
116	is likely to be true (and for C<ecb_unlikel>, that it is unlikely to be	157	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be
117	true).	158	true).
118		159
119	For example, when you check for a 0-ptr and expect this to be a rare,	160	For example, when you check for a null pointer and expect this to be a
120	exceptional, case, then use C<ecb_unlikely>:	161	rare, exceptional, case, then use C<ecb_unlikely>:
121		162
122	void my_free (void *ptr)	163	void my_free (void *ptr)
123	{	164	{
124	if (ecb_unlikely (ptr == 0))	165	if (ecb_unlikely (ptr == 0))
125	return;	166	return;
…		…
129	tell the compiler what the hot path through a function is can increase	170	tell the compiler what the hot path through a function is can increase
130	performance considerably.	171	performance considerably.
131		172
132	A very good example is in a function that reserves more space for some	173	A very good example is in a function that reserves more space for some
133	memory block (for example, inside an implementation of a string stream) -	174	memory block (for example, inside an implementation of a string stream) -
134	eahc time something is added, you have to check for a buffer overrun, but	175	each time something is added, you have to check for a buffer overrun, but
135	you expect that most checks will turn out to be false:	176	you expect that most checks will turn out to be false:
136		177
137	/* make sure we have "size" extra room in our buffer */	178	/* make sure we have "size" extra room in our buffer */
138	ecb_inline void	179	ecb_inline void
139	reserve (int size)	180	reserve (int size)
…		…
173	call will never be executed.	214	call will never be executed.
174		215
175	=item bool ecb_unreachable ()	216	=item bool ecb_unreachable ()
176		217
177	This function does nothing itself, except tell the compiler that it will	218	This function does nothing itself, except tell the compiler that it will
178	never be executed. Apart from supressing a warning in some cases, this	219	never be executed. Apart from suppressing a warning in some cases, this
179	function can be used to implement C<ecb_assume> or similar functions.	220	function can be used to implement C<ecb_assume> or similar functions.
180		221
181	=item bool ecb_prefetch (addr, rw, locality)	222	=item bool ecb_prefetch (addr, rw, locality)
182		223
183	Tells the compiler to try to prefetch memory at the given C<addr>ess	224	Tells the compiler to try to prefetch memory at the given C<addr>ess
184	for either reading (c<rw> = 0) or writing (C<rw> = 1). A C<locality> of	225	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
185	C<0> means that there will only be one access later, C<3> means that	226	C<0> means that there will only be one access later, C<3> means that
186	the data will likely be accessed very often, and values in between mean	227	the data will likely be accessed very often, and values in between mean
187	something... in between. The memory pointed to by the address does not	228	something... in between. The memory pointed to by the address does not
188	need to be accessible (it could be a null pointer for example), but C<rw>	229	need to be accessible (it could be a null pointer for example), but C<rw>
189	and C<locality> must be compile-time constants.	230	and C<locality> must be compile-time constants.
190		231
191	An obvious way to use this is to prefetch some data far away, in a big	232	An obvious way to use this is to prefetch some data far away, in a big
192	array you loop over. This prefethces memory some 128 array elements later,	233	array you loop over. This prefetches memory some 128 array elements later,
193	in the hope that it will be ready when the CPU arrives at that location.	234	in the hope that it will be ready when the CPU arrives at that location.
194		235
195	int sum = 0;	236	int sum = 0;
196		237
197	for (i = 0; i < N; ++i)	238	for (i = 0; i < N; ++i)
…		…
222		263
223	=item bool ecb_big_endian ()	264	=item bool ecb_big_endian ()
224		265
225	=item bool ecb_little_endian ()	266	=item bool ecb_little_endian ()
226		267
		268	These two functions return true if the byte order is big endian
		269	(most-significant byte first) or little endian (least-significant byte
		270	first) respectively.
		271
227	=item int ecb_ctz32 (uint32_t x)	272	=item int ecb_ctz32 (uint32_t x)
228		273
		274	Returns the index of the least significant bit set in C<x> (or
		275	equivalently the number of bits set to 0 before the least significant
		276	bit set), starting from 0. If C<x> is 0 the result is undefined. A
		277	common use case is to compute the integer binary logarithm, i.e.,
		278	floor(log2(n)). For example:
		279
		280	ecb_ctz32(3) = 0
		281	ecb_ctz32(6) = 1
		282
229	=item int ecb_popcount32 (uint32_t x)	283	=item int ecb_popcount32 (uint32_t x)
230		284
		285	Returns the number of bits set to 1 in C<x>. For example:
		286
		287	ecb_popcount32(7) = 3
		288	ecb_popcount32(255) = 8
		289
		290	=item uint32_t ecb_bswap16 (uint32_t x)
		291
231	=item uint32_t ecb_bswap32 (uint32_t x)	292	=item uint32_t ecb_bswap32 (uint32_t x)
232		293
233	=item uint32_t ecb_bswap16 (uint32_t x)	294	These two functions return the value of the 16-bit (32-bit) variable
		295	C<x> after reversing the order of bytes.
234		296
235	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	297	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
236		298
237	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	299	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
238		300
		301	These two functions return the value of C<x> after shifting all the bits
		302	by C<count> positions to the right or left respectively.
		303
239	=back	304	=back
240		305
241	=head2 ARITHMETIC	306	=head2 ARITHMETIC
242		307
243	=over 4	308	=over 4
244		309
245	=item x = ecb_mod (m, n) [MACRO]	310	=item x = ecb_mod (m, n)
		311
		312	Returns the positive remainder of the modulo operation between C<m> and
		313	C<n>. Unlike the C moduloe operator C<%>, this function ensures that the
		314	return value is always positive).
		315
		316	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be
		317	negatable, that is, both C<m> and C<-m> must be representable in its
		318	type.
246		319
247	=back	320	=back
248		321
249	=head2 UTILITY	322	=head2 UTILITY
250		323
251	=over 4	324	=over 4
252		325
253	=item ecb_array_length (name) [MACRO]	326	=item element_count = ecb_array_length (name) [MACRO]
254		327
255	=back	328	Returns the number of elements in the array C<name>. For example:
256		329
		330	int primes[] = { 2, 3, 5, 7, 11 };
		331	int sum = 0;
257		332
		333	for (i = 0; i < ecb_array_length (primes); i++)
		334	sum += primes [i];
		335
		336	=back
		337
		338

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Comparing cvsroot/libecb/ecb.pod (file contents): Revision 1.7 by root, Thu May 26 20:49:40 2011 UTC vs. Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC

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Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.7 by root, Thu May 26 20:49:40 2011 UTC vs.
Revision 1.14 by root, Thu May 26 23:23:08 2011 UTC