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

Comparing libecb/ecb.pod (file contents):
Revision 1.42 by root, Mon May 28 08:54:03 2012 UTC vs.
Revision 1.72 by root, Sat Nov 21 18:09:37 2015 UTC

…		…
60		60
61	ecb.h makes sure that the following types are defined (in the expected way):	61	ecb.h makes sure that the following types are defined (in the expected way):
62		62
63	int8_t uint8_t int16_t uint16_t	63	int8_t uint8_t int16_t uint16_t
64	int32_t uint32_t int64_t uint64_t	64	int32_t uint32_t int64_t uint64_t
65	intptr_t uintptr_t ptrdiff_t	65	intptr_t uintptr_t
66		66
67	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this	67	The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
68	platform (currently C<4> or C<8>).	68	platform (currently C<4> or C<8>) and can be used in preprocessor
		69	expressions.
69		70
		71	For C<ptrdiff_t> and C<size_t> use C<stddef.h>.
		72
		73	=head2 LANGUAGE/ENVIRONMENT/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
		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
70	=head2 GCC ATTRIBUTES	210	=head2 ATTRIBUTES
71		211
72	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
73	attributes that you can assign to functions, variables and sometimes even	213	assigned to functions, variables and sometimes even types - much like
74	types - much like C<const> or C<volatile> in C.	214	C<const> or C<volatile> in C. They are implemented using either GCC
75		215	attributes or other compiler/language specific features. Attributes
76	While GCC allows declarations to show up in many surprising places,
77	but not in many expected places, the safest way is to put attribute
78	declarations before the whole declaration:	216	declarations must be put before the whole declaration:
79		217
80	ecb_const int mysqrt (int a);	218	ecb_const int mysqrt (int a);
81	ecb_unused int i;	219	ecb_unused int i;
82		220
83	For variables, it is often nicer to put the attribute after the name, and
84	avoid multiple declarations using commas:
85
86	int i ecb_unused;
87
88	=over 4	221	=over 4
89
90	=item ecb_attribute ((attrs...))
91
92	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
93	nothing on other compilers, so the effect is that only GCC sees these.
94
95	Example: use the C<deprecated> attribute on a function.
96
97	ecb_attribute((__deprecated__)) void
98	do_not_use_me_anymore (void);
99		222
100	=item ecb_unused	223	=item ecb_unused
101		224
102	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
103	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.
104	declare a variable but do not always use it:	227	declare a variable but do not always use it:
105		228
106	{	229	{
107	int var ecb_unused;	230	ecb_unused int var;
108		231
109	#ifdef SOMECONDITION	232	#ifdef SOMECONDITION
110	var = ...;	233	var = ...;
111	return var;	234	return var;
112	#else	235	#else
113	return 0;	236	return 0;
114	#endif	237	#endif
115	}	238	}
116		239
		240	=item ecb_deprecated
		241
		242	Similar to C<ecb_unused>, but marks a function, variable or type as
		243	deprecated. This makes some compilers warn when the type is used.
		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
117	=item ecb_inline	251	=item ecb_inline
118		252
119	This is not actually an attribute, but you use it like one. It expands
120	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
121	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
122	for code size or speed reasons.	255	inlined, for code size or speed reasons.
123		256
124	Example: inline this function, it surely will reduce codesize.	257	Example: inline this function, it surely will reduce codesize.
125		258
126	ecb_inline int	259	ecb_inline int
127	negmul (int a, int b)	260	negmul (int a, int b)
…		…
129	return - (a * b);	262	return - (a * b);
130	}	263	}
131		264
132	=item ecb_noinline	265	=item ecb_noinline
133		266
134	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
135	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
136	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.
137		270
138	=item ecb_noreturn	271	=item ecb_noreturn
139		272
…		…
149	}	282	}
150		283
151	In this case, the compiler would probably be smart enough to deduce it on	284	In this case, the compiler would probably be smart enough to deduce it on
152	its own, so this is mainly useful for declarations.	285	its own, so this is mainly useful for declarations.
153		286
		287	=item ecb_restrict
		288
		289	Expands to the C<restrict> keyword or equivalent on compilers that support
		290	them, and to nothing on others. Must be specified on a pointer type or
		291	an array index to indicate that the memory doesn't alias with any other
		292	restricted pointer in the same scope.
		293
		294	Example: multiply a vector, and allow the compiler to parallelise the
		295	loop, because it knows it doesn't overwrite input values.
		296
		297	void
		298	multiply (ecb_restrict float *src,
		299	ecb_restrict float *dst,
		300	int len, float factor)
		301	{
		302	int i;
		303
		304	for (i = 0; i < len; ++i)
		305	dst [i] = src [i] * factor;
		306	}
		307
154	=item ecb_const	308	=item ecb_const
155		309
156	Declares that the function only depends on the values of its arguments,	310	Declares that the function only depends on the values of its arguments,
157	much like a mathematical function. It specifically does not read or write	311	much like a mathematical function. It specifically does not read or write
158	any memory any arguments might point to, global variables, or call any	312	any memory any arguments might point to, global variables, or call any
…		…
218	functions only called in exceptional or rare cases.	372	functions only called in exceptional or rare cases.
219		373
220	=item ecb_artificial	374	=item ecb_artificial
221		375
222	Declares the function as "artificial", in this case meaning that this	376	Declares the function as "artificial", in this case meaning that this
223	function is not really mean to be a function, but more like an accessor	377	function is not really meant to be a function, but more like an accessor
224	- many methods in C++ classes are mere accessor functions, and having a	378	- many methods in C++ classes are mere accessor functions, and having a
225	crash reported in such a method, or single-stepping through them, is not	379	crash reported in such a method, or single-stepping through them, is not
226	usually so helpful, especially when it's inlined to just a few instructions.	380	usually so helpful, especially when it's inlined to just a few instructions.
227		381
228	Marking them as artificial will instruct the debugger about just this,	382	Marking them as artificial will instruct the debugger about just this,
…		…
248		402
249	=head2 OPTIMISATION HINTS	403	=head2 OPTIMISATION HINTS
250		404
251	=over 4	405	=over 4
252		406
253	=item bool ecb_is_constant(expr)	407	=item bool ecb_is_constant (expr)
254		408
255	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
256	constant, and false otherwise.	410	constant, and false otherwise.
257		411
258	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
…		…
276	return is_constant (n) && !(n & (n - 1))	430	return is_constant (n) && !(n & (n - 1))
277	? rndm16 () & (num - 1)	431	? rndm16 () & (num - 1)
278	: (n * (uint32_t)rndm16 ()) >> 16;	432	: (n * (uint32_t)rndm16 ()) >> 16;
279	}	433	}
280		434
281	=item bool ecb_expect (expr, value)	435	=item ecb_expect (expr, value)
282		436
283	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
284	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
285	branch optimisations.	439	branch optimisations.
286		440
…		…
333	{	487	{
334	if (ecb_expect_false (current + size > end))	488	if (ecb_expect_false (current + size > end))
335	real_reserve_method (size); /* presumably noinline */	489	real_reserve_method (size); /* presumably noinline */
336	}	490	}
337		491
338	=item bool ecb_assume (cond)	492	=item ecb_assume (cond)
339		493
340	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
341	obvious.	495	obvious. This is not a function, but a statement: it cannot be used in
		496	another expression.
342		497
343	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
344	conditions that might improve code generation, but which are impossible to	499	conditions that might improve code generation, but which are impossible to
345	deduce form the code itself.	500	deduce form the code itself.
346		501
…		…
363		518
364	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
365	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
366	call will never be executed.	521	call will never be executed.
367		522
368	=item bool ecb_unreachable ()	523	=item ecb_unreachable ()
369		524
370	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
371	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
372	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.
373		528
374	=item bool ecb_prefetch (addr, rw, locality)	529	=item ecb_prefetch (addr, rw, locality)
375		530
376	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
377	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
378	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
379	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
380	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
381	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>
382	and C<locality> must be compile-time constants.	537	and C<locality> must be compile-time constants.
383		538
		539	This is a statement, not a function: you cannot use it as part of an
		540	expression.
		541
384	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
385	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,
386	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.
387		545
388	int sum = 0;	546	int sum = 0;
…		…
440		598
441	=item bool ecb_is_pot32 (uint32_t x)	599	=item bool ecb_is_pot32 (uint32_t x)
442		600
443	=item bool ecb_is_pot64 (uint32_t x)	601	=item bool ecb_is_pot64 (uint32_t x)
444		602
445	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>.
446		604
447	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>.
448		606
449	=item int ecb_ld32 (uint32_t x)	607	=item int ecb_ld32 (uint32_t x)
450		608
451	=item int ecb_ld64 (uint64_t x)	609	=item int ecb_ld64 (uint64_t x)
452		610
…		…
521	(C<ecb_rotl>).	679	(C<ecb_rotl>).
522		680
523	Current GCC versions understand these functions and usually compile them	681	Current GCC versions understand these functions and usually compile them
524	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on	682	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
525	x86).	683	x86).
		684
		685	=back
		686
		687	=head2 FLOATING POINT FIDDLING
		688
		689	=over 4
		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
		707	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		708
		709	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		710
		711	These functions each take an argument in the native C<float> or C<double>
		712	type and return the IEEE 754 bit representation of it (binary16/half,
		713	binary32/single or binary64/double precision).
		714
		715	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		716	will be the most significant bit, followed by exponent and mantissa.
		717
		718	This function should work even when the native floating point format isn't
		719	IEEE compliant, of course at a speed and code size penalty, and of course
		720	also within reasonable limits (it tries to convert NaNs, infinities and
		721	denormals, but will likely convert negative zero to positive zero).
		722
		723	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		724	be able to optimise away this function completely.
		725
		726	These functions can be helpful when serialising floats to the network - you
		727	can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
		728
		729	Another use for these functions is to manipulate floating point values
		730	directly.
		731
		732	Silly example: toggle the sign bit of a float.
		733
		734	/* On gcc-4.7 on amd64, */
		735	/* this results in a single add instruction to toggle the bit, and 4 extra */
		736	/* instructions to move the float value to an integer register and back. */
		737
		738	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		739
		740	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		741
		742	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		743
		744	=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
		745
		746	The reverse operation of the previous function - takes the bit
		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
		749	C<double> format.
		750
		751	This function should work even when the native floating point format isn't
		752	IEEE compliant, of course at a speed and code size penalty, and of course
		753	also within reasonable limits (it tries to convert normals and denormals,
		754	and might be lucky for infinities, and with extraordinary luck, also for
		755	negative zero).
		756
		757	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		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-nearest-even, subnormals, infinity
		766	and NaNs) 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.
526		772
527	=back	773	=back
528		774
529	=head2 ARITHMETIC	775	=head2 ARITHMETIC
530		776
…		…
581	for (i = 0; i < ecb_array_length (primes); i++)	827	for (i = 0; i < ecb_array_length (primes); i++)
582	sum += primes [i];	828	sum += primes [i];
583		829
584	=back	830	=back
585		831
		832	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
586		833
		834	These symbols need to be defined before including F<ecb.h> the first time.
		835
		836	=over 4
		837
		838	=item ECB_NO_THREADS
		839
		840	If F<ecb.h> is never used from multiple threads, then this symbol can
		841	be defined, in which case memory fences (and similar constructs) are
		842	completely removed, leading to more efficient code and fewer dependencies.
		843
		844	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		845
		846	=item ECB_NO_SMP
		847
		848	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		849	multiple threads, but never concurrently (e.g. if the system the program
		850	runs on has only a single CPU with a single core, no hyperthreading and so
		851	on), then this symbol can be defined, leading to more efficient code and
		852	fewer dependencies.
		853
		854	=item ECB_NO_LIBM
		855
		856	When defined to C<1>, do not export any functions that might introduce
		857	dependencies on the math library (usually called F<-lm>) - these are
		858	marked with [-UECB_NO_LIBM].
		859
		860	=back
		861
		862	=head1 UNDOCUMENTED FUNCTIONALITY
		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 1.42 by root, Mon May 28 08:54:03 2012 UTC vs. Revision 1.72 by root, Sat Nov 21 18:09:37 2015 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.42 by root, Mon May 28 08:54:03 2012 UTC vs.
Revision 1.72 by root, Sat Nov 21 18:09:37 2015 UTC