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

Comparing libecb/ecb.pod (file contents):
Revision 1.41 by root, Mon May 28 08:40:25 2012 UTC vs.
Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC

…		…
58		58
59	=head2 TYPES / TYPE SUPPORT	59	=head2 TYPES / TYPE SUPPORT
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	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/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
70	=head2 GCC ATTRIBUTES	168	=head2 ATTRIBUTES
71		169
72	A major part of libecb deals with GCC attributes. These are additional	170	A major part of libecb deals with additional attributes that can be
73	attributes that you can assign to functions, variables and sometimes even	171	assigned to functions, variables and sometimes even types - much like
74	types - much like C<const> or C<volatile> in C.	172	C<const> or C<volatile> in C. They are implemented using either GCC
75		173	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:	174	declarations must be put before the whole declaration:
79		175
80	ecb_const int mysqrt (int a);	176	ecb_const int mysqrt (int a);
81	ecb_unused int i;	177	ecb_unused int i;
82		178
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	179	=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		180
100	=item ecb_unused	181	=item ecb_unused
101		182
102	Marks a function or a variable as "unused", which simply suppresses a	183	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.	184	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:	185	declare a variable but do not always use it:
105		186
106	{	187	{
107	int var ecb_unused;	188	ecb_unused int var;
108		189
109	#ifdef SOMECONDITION	190	#ifdef SOMECONDITION
110	var = ...;	191	var = ...;
111	return var;	192	return var;
112	#else	193	#else
113	return 0;	194	return 0;
114	#endif	195	#endif
115	}	196	}
116		197
		198	=item ecb_deprecated
		199
		200	Similar to C<ecb_unused>, but marks a function, variable or type as
		201	deprecated. This makes some compilers warn when the type is used.
		202
117	=item ecb_inline	203	=item ecb_inline
118		204
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	205	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,	206	isn't supported. It should be used to declare functions that should be
122	for code size or speed reasons.	207	inlined, for code size or speed reasons.
123		208
124	Example: inline this function, it surely will reduce codesize.	209	Example: inline this function, it surely will reduce codesize.
125		210
126	ecb_inline int	211	ecb_inline int
127	negmul (int a, int b)	212	negmul (int a, int b)
…		…
149	}	234	}
150		235
151	In this case, the compiler would probably be smart enough to deduce it on	236	In this case, the compiler would probably be smart enough to deduce it on
152	its own, so this is mainly useful for declarations.	237	its own, so this is mainly useful for declarations.
153		238
		239	=item ecb_restrict
		240
		241	Expands to the C<restrict> keyword or equivalent on compilers that support
		242	them, and to nothing on others. Must be specified on a pointer type or
		243	an array index to indicate that the memory doesn't alias with any other
		244	restricted pointer in the same scope.
		245
		246	Example: multiply a vector, and allow the compiler to parallelise the
		247	loop, because it knows it doesn't overwrite input values.
		248
		249	void
		250	multiply (ecb_restrict float *src,
		251	ecb_restrict float *dst,
		252	int len, float factor)
		253	{
		254	int i;
		255
		256	for (i = 0; i < len; ++i)
		257	dst [i] = src [i] * factor;
		258	}
		259
154	=item ecb_const	260	=item ecb_const
155		261
156	Declares that the function only depends on the values of its arguments,	262	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	263	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	264	any memory any arguments might point to, global variables, or call any
…		…
218	functions only called in exceptional or rare cases.	324	functions only called in exceptional or rare cases.
219		325
220	=item ecb_artificial	326	=item ecb_artificial
221		327
222	Declares the function as "artificial", in this case meaning that this	328	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	329	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	330	- 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	331	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.	332	usually so helpful, especially when it's inlined to just a few instructions.
227		333
228	Marking them as artificial will instruct the debugger about just this,	334	Marking them as artificial will instruct the debugger about just this,
…		…
248		354
249	=head2 OPTIMISATION HINTS	355	=head2 OPTIMISATION HINTS
250		356
251	=over 4	357	=over 4
252		358
253	=item bool ecb_is_constant(expr)	359	=item bool ecb_is_constant (expr)
254		360
255	Returns true iff the expression can be deduced to be a compile-time	361	Returns true iff the expression can be deduced to be a compile-time
256	constant, and false otherwise.	362	constant, and false otherwise.
257		363
258	For example, when you have a C<rndm16> function that returns a 16 bit	364	For example, when you have a C<rndm16> function that returns a 16 bit
…		…
524	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on	630	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
525	x86).	631	x86).
526		632
527	=back	633	=back
528		634
		635	=head2 FLOATING POINT FIDDLING
		636
		637	=over 4
		638
		639	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		640
		641	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		642
		643	These functions each take an argument in the native C<float> or C<double>
		644	type and return the IEEE 754 bit representation of it.
		645
		646	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		647	will be the most significant bit, followed by exponent and mantissa.
		648
		649	This function should work even when the native floating point format isn't
		650	IEEE compliant, of course at a speed and code size penalty, and of course
		651	also within reasonable limits (it tries to convert NaNs, infinities and
		652	denormals, but will likely convert negative zero to positive zero).
		653
		654	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		655	be able to optimise away this function completely.
		656
		657	These functions can be helpful when serialising floats to the network - you
		658	can serialise the return value like a normal uint32_t/uint64_t.
		659
		660	Another use for these functions is to manipulate floating point values
		661	directly.
		662
		663	Silly example: toggle the sign bit of a float.
		664
		665	/* On gcc-4.7 on amd64, */
		666	/* this results in a single add instruction to toggle the bit, and 4 extra */
		667	/* instructions to move the float value to an integer register and back. */
		668
		669	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		670
		671	=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
		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 previous function - takes the bit
		678	representation of an IEEE binary16, binary32 or binary64 number and
		679	converts it to the native C<float> 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
529	=head2 ARITHMETIC	692	=head2 ARITHMETIC
530		693
531	=over 4	694	=over 4
532		695
533	=item x = ecb_mod (m, n)	696	=item x = ecb_mod (m, n)
…		…
581	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
582	sum += primes [i];	745	sum += primes [i];
583		746
584	=back	747	=back
585		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
586		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

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libecb/ecb.pod (file contents): Revision 1.41 by root, Mon May 28 08:40:25 2012 UTC vs. Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC

Diff Legend

Comparing libecb/ecb.pod (file contents):
Revision 1.41 by root, Mon May 28 08:40:25 2012 UTC vs.
Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC