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

Comparing libecb/ecb.pod (file contents):
Revision 1.57 by root, Thu Oct 16 14:47:20 2014 UTC vs.
Revision 1.71 by root, Sat Nov 21 16:53:50 2015 UTC

…		…
68	platform (currently C<4> or C<8>) and can be used in preprocessor	68	platform (currently C<4> or C<8>) and can be used in preprocessor
69	expressions.	69	expressions.
70		70
71	For C<ptrdiff_t> and C<size_t> use C<stddef.h>.	71	For C<ptrdiff_t> and C<size_t> use C<stddef.h>.
72		72
73	=head2 LANGUAGE/COMPILER VERSIONS	73	=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
74		74
75	All the following symbols expand to an expression that can be tested in	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	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).	77	ensure it's either C<0> or C<1> if you need that).
78		78
…		…
163	C<__x86_64> stands for, well, the x86-64 ABI, making these macros	163	C<__x86_64> stands for, well, the x86-64 ABI, making these macros
164	necessary.	164	necessary.
165		165
166	=back	166	=back
167		167
		168	=head2 MACRO TRICKERY
		169
		170	=over 4
		171
		172	=item ECB_CONCAT (a, b)
		173
		174	Expands any macros in C<a> and C<b>, then concatenates the result to form
		175	a single token. This is mainly useful to form identifiers from components,
		176	e.g.:
		177
		178	#define S1 str
		179	#define S2 cpy
		180
		181	ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
		182
		183	=item ECB_STRINGIFY (arg)
		184
		185	Expands any macros in C<arg> and returns the stringified version of
		186	it. This is mainly useful to get the contents of a macro in string form,
		187	e.g.:
		188
		189	#define SQL_LIMIT 100
		190	sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
		191
		192	=item ECB_STRINGIFY_EXPR (expr)
		193
		194	Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
		195	is a valid expression. This is useful to catch typos or cases where the
		196	macro isn't available:
		197
		198	#include <errno.h>
		199
		200	ECB_STRINGIFY (EDOM); // "33" (on my system at least)
		201	ECB_STRINGIFY_EXPR (EDOM); // "33"
		202
		203	// now imagine we had a typo:
		204
		205	ECB_STRINGIFY (EDAM); // "EDAM"
		206	ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
		207
		208	=back
		209
168	=head2 GCC ATTRIBUTES	210	=head2 ATTRIBUTES
169		211
170	A major part of libecb deals with GCC attributes. These are additional	212	A major part of libecb deals with additional attributes that can be
171	attributes that you can assign to functions, variables and sometimes even	213	assigned to functions, variables and sometimes even types - much like
172	types - much like C<const> or C<volatile> in C.	214	C<const> or C<volatile> in C. They are implemented using either GCC
173		215	attributes or other compiler/language specific features. Attributes
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:	216	declarations must be put before the whole declaration:
177		217
178	ecb_const int mysqrt (int a);	218	ecb_const int mysqrt (int a);
179	ecb_unused int i;	219	ecb_unused int i;
180		220
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;
185
186	=over 4	221	=over 4
187
188	=item ecb_attribute ((attrs...))
189
190	A simple wrapper that expands to C<__attribute__((attrs))> on GCC 3.1+ and
191	Clang 2.8+, and to nothing on other compilers, so the effect is that only
192	GCC and Clang see these.
193
194	Example: use the C<deprecated> attribute on a function.
195
196	ecb_attribute((__deprecated__)) void
197	do_not_use_me_anymore (void);
198		222
199	=item ecb_unused	223	=item ecb_unused
200		224
201	Marks a function or a variable as "unused", which simply suppresses a	225	Marks a function or a variable as "unused", which simply suppresses a
202	warning by GCC when it detects it as unused. This is useful when you e.g.	226	warning by GCC when it detects it as unused. This is useful when you e.g.
203	declare a variable but do not always use it:	227	declare a variable but do not always use it:
204		228
205	{	229	{
206	int var ecb_unused;	230	ecb_unused int var;
207		231
208	#ifdef SOMECONDITION	232	#ifdef SOMECONDITION
209	var = ...;	233	var = ...;
210	return var;	234	return var;
211	#else	235	#else
…		…
216	=item ecb_deprecated	240	=item ecb_deprecated
217		241
218	Similar to C<ecb_unused>, but marks a function, variable or type as	242	Similar to C<ecb_unused>, but marks a function, variable or type as
219	deprecated. This makes some compilers warn when the type is used.	243	deprecated. This makes some compilers warn when the type is used.
220		244
		245	=item ecb_deprecated_message (message)
		246
		247	Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
		248	used instead of a generic depreciation message when the object is being
		249	used.
		250
221	=item ecb_inline	251	=item ecb_inline
222		252
223	This is not actually an attribute, but you use it like one. It expands
224	either to C<static inline> or to just C<static>, if inline isn't	253	Expands either to C<static inline> or to just C<static>, if inline
225	supported. It should be used to declare functions that should be inlined,	254	isn't supported. It should be used to declare functions that should be
226	for code size or speed reasons.	255	inlined, for code size or speed reasons.
227		256
228	Example: inline this function, it surely will reduce codesize.	257	Example: inline this function, it surely will reduce codesize.
229		258
230	ecb_inline int	259	ecb_inline int
231	negmul (int a, int b)	260	negmul (int a, int b)
…		…
233	return - (a * b);	262	return - (a * b);
234	}	263	}
235		264
236	=item ecb_noinline	265	=item ecb_noinline
237		266
238	Prevent a function from being inlined - it might be optimised away, but	267	Prevents a function from being inlined - it might be optimised away, but
239	not inlined into other functions. This is useful if you know your function	268	not inlined into other functions. This is useful if you know your function
240	is rarely called and large enough for inlining not to be helpful.	269	is rarely called and large enough for inlining not to be helpful.
241		270
242	=item ecb_noreturn	271	=item ecb_noreturn
243		272
…		…
264		293
265	Example: multiply a vector, and allow the compiler to parallelise the	294	Example: multiply a vector, and allow the compiler to parallelise the
266	loop, because it knows it doesn't overwrite input values.	295	loop, because it knows it doesn't overwrite input values.
267		296
268	void	297	void
269	multiply (float *ecb_restrict src,	298	multiply (ecb_restrict float *src,
270	float *ecb_restrict dst,	299	ecb_restrict float *dst,
271	int len, float factor)	300	int len, float factor)
272	{	301	{
273	int i;	302	int i;
274		303
275	for (i = 0; i < len; ++i)	304	for (i = 0; i < len; ++i)
…		…
373		402
374	=head2 OPTIMISATION HINTS	403	=head2 OPTIMISATION HINTS
375		404
376	=over 4	405	=over 4
377		406
378	=item bool ecb_is_constant(expr)	407	=item bool ecb_is_constant (expr)
379		408
380	Returns true iff the expression can be deduced to be a compile-time	409	Returns true iff the expression can be deduced to be a compile-time
381	constant, and false otherwise.	410	constant, and false otherwise.
382		411
383	For example, when you have a C<rndm16> function that returns a 16 bit	412	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
401	return is_constant (n) && !(n & (n - 1))	430	return is_constant (n) && !(n & (n - 1))
402	? rndm16 () & (num - 1)	431	? rndm16 () & (num - 1)
403	: (n * (uint32_t)rndm16 ()) >> 16;	432	: (n * (uint32_t)rndm16 ()) >> 16;
404	}	433	}
405		434
406	=item bool ecb_expect (expr, value)	435	=item ecb_expect (expr, value)
407		436
408	Evaluates C<expr> and returns it. In addition, it tells the compiler that	437	Evaluates C<expr> and returns it. In addition, it tells the compiler that
409	the C<expr> evaluates to C<value> a lot, which can be used for static	438	the C<expr> evaluates to C<value> a lot, which can be used for static
410	branch optimisations.	439	branch optimisations.
411		440
…		…
458	{	487	{
459	if (ecb_expect_false (current + size > end))	488	if (ecb_expect_false (current + size > end))
460	real_reserve_method (size); /* presumably noinline */	489	real_reserve_method (size); /* presumably noinline */
461	}	490	}
462		491
463	=item bool ecb_assume (cond)	492	=item ecb_assume (cond)
464		493
465	Try to tell the compiler that some condition is true, even if it's not	494	Tries to tell the compiler that some condition is true, even if it's not
466	obvious.	495	obvious. This is not a function, but a statement: it cannot be used in
		496	another expression.
467		497
468	This can be used to teach the compiler about invariants or other	498	This can be used to teach the compiler about invariants or other
469	conditions that might improve code generation, but which are impossible to	499	conditions that might improve code generation, but which are impossible to
470	deduce form the code itself.	500	deduce form the code itself.
471		501
…		…
488		518
489	Then the compiler I<might> be able to optimise out the second call	519	Then the compiler I<might> be able to optimise out the second call
490	completely, as it knows that C<< current + 1 > end >> is false and the	520	completely, as it knows that C<< current + 1 > end >> is false and the
491	call will never be executed.	521	call will never be executed.
492		522
493	=item bool ecb_unreachable ()	523	=item ecb_unreachable ()
494		524
495	This function does nothing itself, except tell the compiler that it will	525	This function does nothing itself, except tell the compiler that it will
496	never be executed. Apart from suppressing a warning in some cases, this	526	never be executed. Apart from suppressing a warning in some cases, this
497	function can be used to implement C<ecb_assume> or similar functions.	527	function can be used to implement C<ecb_assume> or similar functionality.
498		528
499	=item bool ecb_prefetch (addr, rw, locality)	529	=item ecb_prefetch (addr, rw, locality)
500		530
501	Tells the compiler to try to prefetch memory at the given C<addr>ess	531	Tells the compiler to try to prefetch memory at the given C<addr>ess
502	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of	532	for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
503	C<0> means that there will only be one access later, C<3> means that	533	C<0> means that there will only be one access later, C<3> means that
504	the data will likely be accessed very often, and values in between mean	534	the data will likely be accessed very often, and values in between mean
505	something... in between. The memory pointed to by the address does not	535	something... in between. The memory pointed to by the address does not
506	need to be accessible (it could be a null pointer for example), but C<rw>	536	need to be accessible (it could be a null pointer for example), but C<rw>
507	and C<locality> must be compile-time constants.	537	and C<locality> must be compile-time constants.
508		538
		539	This is a statement, not a function: you cannot use it as part of an
		540	expression.
		541
509	An obvious way to use this is to prefetch some data far away, in a big	542	An obvious way to use this is to prefetch some data far away, in a big
510	array you loop over. This prefetches memory some 128 array elements later,	543	array you loop over. This prefetches memory some 128 array elements later,
511	in the hope that it will be ready when the CPU arrives at that location.	544	in the hope that it will be ready when the CPU arrives at that location.
512		545
513	int sum = 0;	546	int sum = 0;
…		…
565		598
566	=item bool ecb_is_pot32 (uint32_t x)	599	=item bool ecb_is_pot32 (uint32_t x)
567		600
568	=item bool ecb_is_pot64 (uint32_t x)	601	=item bool ecb_is_pot64 (uint32_t x)
569		602
570	Return true iff C<x> is a power of two or C<x == 0>.	603	Returns true iff C<x> is a power of two or C<x == 0>.
571		604
572	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.	605	For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
573		606
574	=item int ecb_ld32 (uint32_t x)	607	=item int ecb_ld32 (uint32_t x)
575		608
576	=item int ecb_ld64 (uint64_t x)	609	=item int ecb_ld64 (uint64_t x)
577		610
…		…
653		686
654	=head2 FLOATING POINT FIDDLING	687	=head2 FLOATING POINT FIDDLING
655		688
656	=over 4	689	=over 4
657		690
		691	=item ECB_INFINITY [-UECB_NO_LIBM]
		692
		693	Evaluates to positive infinity if supported by the platform, otherwise to
		694	a truly huge number.
		695
		696	=item ECB_NAN [-UECB_NO_LIBM]
		697
		698	Evaluates to a quiet NAN if supported by the platform, otherwise to
		699	C<ECB_INFINITY>.
		700
		701	=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
		702
		703	Same as C<ldexpf>, but always available.
		704
		705	=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
		706
658	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]	707	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
659		708
660	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]	709	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
661		710
662	These functions each take an argument in the native C<float> or C<double>	711	These functions each take an argument in the native C<float> or C<double>
663	type and return the IEEE 754 bit representation of it.	712	type and return the IEEE 754 bit representation of it (binary16/half,
		713	binary32/single or binary64/double precision).
664		714
665	The bit representation is just as IEEE 754 defines it, i.e. the sign bit	715	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
666	will be the most significant bit, followed by exponent and mantissa.	716	will be the most significant bit, followed by exponent and mantissa.
667		717
668	This function should work even when the native floating point format isn't	718	This function should work even when the native floating point format isn't
…		…
672		722
673	On all modern platforms (where C<ECB_STDFP> is true), the compiler should	723	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
674	be able to optimise away this function completely.	724	be able to optimise away this function completely.
675		725
676	These functions can be helpful when serialising floats to the network - you	726	These functions can be helpful when serialising floats to the network - you
677	can serialise the return value like a normal uint32_t/uint64_t.	727	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
678		728
679	Another use for these functions is to manipulate floating point values	729	Another use for these functions is to manipulate floating point values
680	directly.	730	directly.
681		731
682	Silly example: toggle the sign bit of a float.	732	Silly example: toggle the sign bit of a float.
…		…
685	/* this results in a single add instruction to toggle the bit, and 4 extra */	735	/* this results in a single add instruction to toggle the bit, and 4 extra */
686	/* instructions to move the float value to an integer register and back. */	736	/* instructions to move the float value to an integer register and back. */
687		737
688	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)	738	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
689		739
		740	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		741
690	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]	742	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
691		743
692	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]	744	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
693		745
694	The reverse operation of the previos function - takes the bit representation	746	The reverse operation of the previous function - takes the bit
695	of an IEEE binary32 or binary64 number and converts it to the native C<float>	747	representation of an IEEE binary16, binary32 or binary64 number (half,
		748	single or double precision) and converts it to the native C<float> or
696	or C<double> format.	749	C<double> format.
697		750
698	This function should work even when the native floating point format isn't	751	This function should work even when the native floating point format isn't
699	IEEE compliant, of course at a speed and code size penalty, and of course	752	IEEE compliant, of course at a speed and code size penalty, and of course
700	also within reasonable limits (it tries to convert normals and denormals,	753	also within reasonable limits (it tries to convert normals and denormals,
701	and might be lucky for infinities, and with extraordinary luck, also for	754	and might be lucky for infinities, and with extraordinary luck, also for
702	negative zero).	755	negative zero).
703		756
704	On all modern platforms (where C<ECB_STDFP> is true), the compiler should	757	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
705	be able to optimise away this function completely.	758	be able to optimise away this function completely.
		759
		760	=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
		761
		762	=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
		763
		764	Convert a IEEE binary32/single precision to binary16/half format, and vice
		765	versa, handling all details (round-to-even, subnormals, infinity and NaNs)
		766	correctly.
		767
		768	These are functions are available under C<-DECB_NO_LIBM>, since
		769	they do not rely on the platform floating point format. The
		770	C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
		771	usually what you want.
706		772
707	=back	773	=back
708		774
709	=head2 ARITHMETIC	775	=head2 ARITHMETIC
710		776
…		…
791	dependencies on the math library (usually called F<-lm>) - these are	857	dependencies on the math library (usually called F<-lm>) - these are
792	marked with [-UECB_NO_LIBM].	858	marked with [-UECB_NO_LIBM].
793		859
794	=back	860	=back
795		861
		862	=head1 UNDOCUMENTED FUNCTIONALITY
796		863
		864	F<ecb.h> is full of undocumented functionality as well, some of which is
		865	intended to be internal-use only, some of which we forgot to document, and
		866	some of which we hide because we are not sure we will keep the interface
		867	stable.
		868
		869	While you are welcome to rummage around and use whatever you find useful
		870	(we can't stop you), keep in mind that we will change undocumented
		871	functionality in incompatible ways without thinking twice, while we are
		872	considerably more conservative with documented things.
		873
		874	=head1 AUTHORS
		875
		876	C<libecb> is designed and maintained by:
		877
		878	Emanuele Giaquinta <e.giaquinta@glauco.it>
		879	Marc Alexander Lehmann <schmorp@schmorp.de>
		880
		881

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Comparing libecb/ecb.pod (file contents): Revision 1.57 by root, Thu Oct 16 14:47:20 2014 UTC vs. Revision 1.71 by root, Sat Nov 21 16:53:50 2015 UTC

Diff Legend

Comparing libecb/ecb.pod (file contents):
Revision 1.57 by root, Thu Oct 16 14:47:20 2014 UTC vs.
Revision 1.71 by root, Sat Nov 21 16:53:50 2015 UTC