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

Comparing libecb/ecb.pod (file contents):
Revision 1.32 by sf-exg, Fri Jun 17 15:55:41 2011 UTC vs.
Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC

…		…
54	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
55	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
56	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
57	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
58		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	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
59	=head2 GCC ATTRIBUTES	168	=head2 ATTRIBUTES
60		169
61	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
62	attributes that you can assign to functions, variables and sometimes even	171	assigned to functions, variables and sometimes even types - much like
63	types - much like C<const> or C<volatile> in C.	172	C<const> or C<volatile> in C. They are implemented using either GCC
64		173	attributes or other compiler/language specific features. Attributes
65	While GCC allows declarations to show up in many surprising places,
66	but not in many expected places, the safest way is to put attribute
67	declarations before the whole declaration:	174	declarations must be put before the whole declaration:
68		175
69	ecb_const int mysqrt (int a);	176	ecb_const int mysqrt (int a);
70	ecb_unused int i;	177	ecb_unused int i;
71		178
72	For variables, it is often nicer to put the attribute after the name, and
73	avoid multiple declarations using commas:
74
75	int i ecb_unused;
76
77	=over 4	179	=over 4
78
79	=item ecb_attribute ((attrs...))
80
81	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
82	nothing on other compilers, so the effect is that only GCC sees these.
83
84	Example: use the C<deprecated> attribute on a function.
85
86	ecb_attribute((__deprecated__)) void
87	do_not_use_me_anymore (void);
88		180
89	=item ecb_unused	181	=item ecb_unused
90		182
91	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
92	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.
…		…
101	#else	193	#else
102	return 0;	194	return 0;
103	#endif	195	#endif
104	}	196	}
105		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
106	=item ecb_inline	203	=item ecb_inline
107		204
108	This is not actually an attribute, but you use it like one. It expands
109	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
110	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
111	for code size or speed reasons.	207	inlined, for code size or speed reasons.
112		208
113	Example: inline this function, it surely will reduce codesize.	209	Example: inline this function, it surely will reduce codesize.
114		210
115	ecb_inline int	211	ecb_inline int
116	negmul (int a, int b)	212	negmul (int a, int b)
…		…
138	}	234	}
139		235
140	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
141	its own, so this is mainly useful for declarations.	237	its own, so this is mainly useful for declarations.
142		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 (float *ecb_restrict src,
		251	float *ecb_restrict 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
143	=item ecb_const	260	=item ecb_const
144		261
145	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,
146	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
147	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
…		…
207	functions only called in exceptional or rare cases.	324	functions only called in exceptional or rare cases.
208		325
209	=item ecb_artificial	326	=item ecb_artificial
210		327
211	Declares the function as "artificial", in this case meaning that this	328	Declares the function as "artificial", in this case meaning that this
212	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
213	- 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
214	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
215	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.
216		333
217	Marking them as artificial will instruct the debugger about just this,	334	Marking them as artificial will instruct the debugger about just this,
…		…
237		354
238	=head2 OPTIMISATION HINTS	355	=head2 OPTIMISATION HINTS
239		356
240	=over 4	357	=over 4
241		358
242	=item bool ecb_is_constant(expr)	359	=item bool ecb_is_constant (expr)
243		360
244	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
245	constant, and false otherwise.	362	constant, and false otherwise.
246		363
247	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
…		…
396	After processing the node, (part of) the next node might already be in	513	After processing the node, (part of) the next node might already be in
397	cache.	514	cache.
398		515
399	=back	516	=back
400		517
401	=head2 BIT FIDDLING / BITSTUFFS	518	=head2 BIT FIDDLING / BIT WIZARDRY
402		519
403	=over 4	520	=over 4
404		521
405	=item bool ecb_big_endian ()	522	=item bool ecb_big_endian ()
406		523
…		…
412		529
413	On systems that are neither, their return values are unspecified.	530	On systems that are neither, their return values are unspecified.
414		531
415	=item int ecb_ctz32 (uint32_t x)	532	=item int ecb_ctz32 (uint32_t x)
416		533
		534	=item int ecb_ctz64 (uint64_t x)
		535
417	Returns the index of the least significant bit set in C<x> (or	536	Returns the index of the least significant bit set in C<x> (or
418	equivalently the number of bits set to 0 before the least significant bit	537	equivalently the number of bits set to 0 before the least significant bit
419	set), starting from 0. If C<x> is 0 the result is undefined. For example:	538	set), starting from 0. If C<x> is 0 the result is undefined.
		539
		540	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		541
		542	For example:
420		543
421	ecb_ctz32 (3) = 0	544	ecb_ctz32 (3) = 0
422	ecb_ctz32 (6) = 1	545	ecb_ctz32 (6) = 1
423		546
		547	=item bool ecb_is_pot32 (uint32_t x)
		548
		549	=item bool ecb_is_pot64 (uint32_t x)
		550
		551	Return true iff C<x> is a power of two or C<x == 0>.
		552
		553	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		554
		555	=item int ecb_ld32 (uint32_t x)
		556
		557	=item int ecb_ld64 (uint64_t x)
		558
		559	Returns the index of the most significant bit set in C<x>, or the number
		560	of digits the number requires in binary (so that C<< 2**ld <= x <
		561	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		562	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		563	example to see how many bits a certain number requires to be encoded.
		564
		565	This function is similar to the "count leading zero bits" function, except
		566	that that one returns how many zero bits are "in front" of the number (in
		567	the given data type), while C<ecb_ld> returns how many bits the number
		568	itself requires.
		569
		570	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		571
424	=item int ecb_popcount32 (uint32_t x)	572	=item int ecb_popcount32 (uint32_t x)
425		573
		574	=item int ecb_popcount64 (uint64_t x)
		575
426	Returns the number of bits set to 1 in C<x>. For example:	576	Returns the number of bits set to 1 in C<x>.
		577
		578	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		579
		580	For example:
427		581
428	ecb_popcount32 (7) = 3	582	ecb_popcount32 (7) = 3
429	ecb_popcount32 (255) = 8	583	ecb_popcount32 (255) = 8
430		584
		585	=item uint8_t ecb_bitrev8 (uint8_t x)
		586
		587	=item uint16_t ecb_bitrev16 (uint16_t x)
		588
		589	=item uint32_t ecb_bitrev32 (uint32_t x)
		590
		591	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		592	and so on.
		593
		594	Example:
		595
		596	ecb_bitrev8 (0xa7) = 0xea
		597	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		598
431	=item uint32_t ecb_bswap16 (uint32_t x)	599	=item uint32_t ecb_bswap16 (uint32_t x)
432		600
433	=item uint32_t ecb_bswap32 (uint32_t x)	601	=item uint32_t ecb_bswap32 (uint32_t x)
434		602
		603	=item uint64_t ecb_bswap64 (uint64_t x)
		604
435	These two functions return the value of the 16-bit (32-bit) value C<x>	605	These functions return the value of the 16-bit (32-bit, 64-bit) value
436	after reversing the order of bytes (0x11223344 becomes 0x44332211).	606	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		607	C<ecb_bswap32>).
		608
		609	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		610
		611	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		612
		613	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		614
		615	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		616
		617	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		618
		619	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
437		620
438	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	621	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
439		622
440	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	623	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
441		624
442	These two functions return the value of C<x> after rotating all the bits	625	These two families of functions return the value of C<x> after rotating
443	by C<count> positions to the right or left respectively.	626	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		627	(C<ecb_rotl>).
444		628
445	Current GCC versions understand these functions and usually compile them	629	Current GCC versions understand these functions and usually compile them
446	to "optimal" code (e.g. a single C<roll> on x86).	630	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		631	x86).
		632
		633	=back
		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.
447		689
448	=back	690	=back
449		691
450	=head2 ARITHMETIC	692	=head2 ARITHMETIC
451		693
…		…
475	change direction for negative values:	717	change direction for negative values:
476		718
477	for (m = -100; m <= 100; ++m)	719	for (m = -100; m <= 100; ++m)
478	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];	720	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
479		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++.
		730
480	=back	731	=back
481		732
482	=head2 UTILITY	733	=head2 UTILITY
483		734
484	=over 4	735	=over 4
…		…
493	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
494	sum += primes [i];	745	sum += primes [i];
495		746
496	=back	747	=back
497		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
498		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 1.32 by sf-exg, Fri Jun 17 15:55:41 2011 UTC vs. Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.32 by sf-exg, Fri Jun 17 15:55:41 2011 UTC vs.
Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC