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

Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.27 by root, Wed Jun 1 01:29:36 2011 UTC vs.
Revision 1.54 by root, Wed Dec 19 23:33:47 2012 UTC

…		…
53	C<uint32_t>, then the corresponding function works only with that type. If	53	C<uint32_t>, then the corresponding function works only with that type. If
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
		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	which is typically true for both C and C++ compilers.
		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.
		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.
		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
58		167
59	=head2 GCC ATTRIBUTES	168	=head2 GCC ATTRIBUTES
60		169
61	A major part of libecb deals with GCC attributes. These are additional	170	A major part of libecb deals with GCC attributes. These are additional
62	attributes that you can assign to functions, variables and sometimes even	171	attributes that you can assign to functions, variables and sometimes even
…		…
101	#else	210	#else
102	return 0;	211	return 0;
103	#endif	212	#endif
104	}	213	}
105		214
		215	=item ecb_inline
		216
		217	This is not actually an attribute, but you use it like one. It expands
		218	either to C<static inline> or to just C<static>, if inline isn't
		219	supported. It should be used to declare functions that should be inlined,
		220	for code size or speed reasons.
		221
		222	Example: inline this function, it surely will reduce codesize.
		223
		224	ecb_inline int
		225	negmul (int a, int b)
		226	{
		227	return - (a * b);
		228	}
		229
106	=item ecb_noinline	230	=item ecb_noinline
107		231
108	Prevent a function from being inlined - it might be optimised away, but	232	Prevent a function from being inlined - it might be optimised away, but
109	not inlined into other functions. This is useful if you know your function	233	not inlined into other functions. This is useful if you know your function
110	is rarely called and large enough for inlining not to be helpful.	234	is rarely called and large enough for inlining not to be helpful.
…		…
123	}	247	}
124		248
125	In this case, the compiler would probably be smart enough to deduce it on	249	In this case, the compiler would probably be smart enough to deduce it on
126	its own, so this is mainly useful for declarations.	250	its own, so this is mainly useful for declarations.
127		251
		252	=item ecb_restrict
		253
		254	Expands to the C<restrict> keyword or equivalent on compilers that support
		255	them, and to nothing on others. Must be specified on a pointer type or
		256	an array index to indicate that the memory doesn't alias with any other
		257	restricted pointer in the same scope.
		258
		259	Example: multiply a vector, and allow the compiler to parallelise the
		260	loop, because it knows it doesn't overwrite input values.
		261
		262	void
		263	multiply (float *ecb_restrict src,
		264	float *ecb_restrict dst,
		265	int len, float factor)
		266	{
		267	int i;
		268
		269	for (i = 0; i < len; ++i)
		270	dst [i] = src [i] * factor;
		271	}
		272
128	=item ecb_const	273	=item ecb_const
129		274
130	Declares that the function only depends on the values of its arguments,	275	Declares that the function only depends on the values of its arguments,
131	much like a mathematical function. It specifically does not read or write	276	much like a mathematical function. It specifically does not read or write
132	any memory any arguments might point to, global variables, or call any	277	any memory any arguments might point to, global variables, or call any
…		…
192	functions only called in exceptional or rare cases.	337	functions only called in exceptional or rare cases.
193		338
194	=item ecb_artificial	339	=item ecb_artificial
195		340
196	Declares the function as "artificial", in this case meaning that this	341	Declares the function as "artificial", in this case meaning that this
197	function is not really mean to be a function, but more like an accessor	342	function is not really meant to be a function, but more like an accessor
198	- many methods in C++ classes are mere accessor functions, and having a	343	- many methods in C++ classes are mere accessor functions, and having a
199	crash reported in such a method, or single-stepping through them, is not	344	crash reported in such a method, or single-stepping through them, is not
200	usually so helpful, especially when it's inlined to just a few instructions.	345	usually so helpful, especially when it's inlined to just a few instructions.
201		346
202	Marking them as artificial will instruct the debugger about just this,	347	Marking them as artificial will instruct the debugger about just this,
…		…
381	After processing the node, (part of) the next node might already be in	526	After processing the node, (part of) the next node might already be in
382	cache.	527	cache.
383		528
384	=back	529	=back
385		530
386	=head2 BIT FIDDLING / BITSTUFFS	531	=head2 BIT FIDDLING / BIT WIZARDRY
387		532
388	=over 4	533	=over 4
389		534
390	=item bool ecb_big_endian ()	535	=item bool ecb_big_endian ()
391		536
…		…
397		542
398	On systems that are neither, their return values are unspecified.	543	On systems that are neither, their return values are unspecified.
399		544
400	=item int ecb_ctz32 (uint32_t x)	545	=item int ecb_ctz32 (uint32_t x)
401		546
		547	=item int ecb_ctz64 (uint64_t x)
		548
402	Returns the index of the least significant bit set in C<x> (or	549	Returns the index of the least significant bit set in C<x> (or
403	equivalently the number of bits set to 0 before the least significant bit	550	equivalently the number of bits set to 0 before the least significant bit
404	set), starting from 0. If C<x> is 0 the result is undefined. A common use	551	set), starting from 0. If C<x> is 0 the result is undefined.
405	case is to compute the integer binary logarithm, i.e., C<floor (log2	552
		553	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		554
406	(n))>. For example:	555	For example:
407		556
408	ecb_ctz32 (3) = 0	557	ecb_ctz32 (3) = 0
409	ecb_ctz32 (6) = 1	558	ecb_ctz32 (6) = 1
410		559
		560	=item bool ecb_is_pot32 (uint32_t x)
		561
		562	=item bool ecb_is_pot64 (uint32_t x)
		563
		564	Return true iff C<x> is a power of two or C<x == 0>.
		565
		566	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		567
		568	=item int ecb_ld32 (uint32_t x)
		569
		570	=item int ecb_ld64 (uint64_t x)
		571
		572	Returns the index of the most significant bit set in C<x>, or the number
		573	of digits the number requires in binary (so that C<< 2**ld <= x <
		574	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		575	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		576	example to see how many bits a certain number requires to be encoded.
		577
		578	This function is similar to the "count leading zero bits" function, except
		579	that that one returns how many zero bits are "in front" of the number (in
		580	the given data type), while C<ecb_ld> returns how many bits the number
		581	itself requires.
		582
		583	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		584
411	=item int ecb_popcount32 (uint32_t x)	585	=item int ecb_popcount32 (uint32_t x)
412		586
		587	=item int ecb_popcount64 (uint64_t x)
		588
413	Returns the number of bits set to 1 in C<x>. For example:	589	Returns the number of bits set to 1 in C<x>.
		590
		591	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		592
		593	For example:
414		594
415	ecb_popcount32 (7) = 3	595	ecb_popcount32 (7) = 3
416	ecb_popcount32 (255) = 8	596	ecb_popcount32 (255) = 8
417		597
		598	=item uint8_t ecb_bitrev8 (uint8_t x)
		599
		600	=item uint16_t ecb_bitrev16 (uint16_t x)
		601
		602	=item uint32_t ecb_bitrev32 (uint32_t x)
		603
		604	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		605	and so on.
		606
		607	Example:
		608
		609	ecb_bitrev8 (0xa7) = 0xea
		610	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		611
418	=item uint32_t ecb_bswap16 (uint32_t x)	612	=item uint32_t ecb_bswap16 (uint32_t x)
419		613
420	=item uint32_t ecb_bswap32 (uint32_t x)	614	=item uint32_t ecb_bswap32 (uint32_t x)
421		615
		616	=item uint64_t ecb_bswap64 (uint64_t x)
		617
422	These two functions return the value of the 16-bit (32-bit) value C<x>	618	These functions return the value of the 16-bit (32-bit, 64-bit) value
423	after reversing the order of bytes (0x11223344 becomes 0x44332211).	619	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		620	C<ecb_bswap32>).
		621
		622	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		623
		624	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		625
		626	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		627
		628	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		629
		630	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		631
		632	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
424		633
425	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	634	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
426		635
427	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	636	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
428		637
429	These two functions return the value of C<x> after rotating all the bits	638	These two families of functions return the value of C<x> after rotating
430	by C<count> positions to the right or left respectively.	639	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		640	(C<ecb_rotl>).
431		641
432	Current GCC versions understand these functions and usually compile them	642	Current GCC versions understand these functions and usually compile them
433	to "optimal" code (e.g. a single C<roll> on x86).	643	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		644	x86).
		645
		646	=back
		647
		648	=head2 FLOATING POINT FIDDLING
		649
		650	=over 4
		651
		652	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		653
		654	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		655
		656	These functions each take an argument in the native C<float> or C<double>
		657	type and return the IEEE 754 bit representation of it.
		658
		659	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		660	will be the most significant bit, followed by exponent and mantissa.
		661
		662	This function should work even when the native floating point format isn't
		663	IEEE compliant, of course at a speed and code size penalty, and of course
		664	also within reasonable limits (it tries to convert NaNs, infinities and
		665	denormals, but will likely convert negative zero to positive zero).
		666
		667	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		668	be able to optimise away this function completely.
		669
		670	These functions can be helpful when serialising floats to the network - you
		671	can serialise the return value like a normal uint32_t/uint64_t.
		672
		673	Another use for these functions is to manipulate floating point values
		674	directly.
		675
		676	Silly example: toggle the sign bit of a float.
		677
		678	/* On gcc-4.7 on amd64, */
		679	/* this results in a single add instruction to toggle the bit, and 4 extra */
		680	/* instructions to move the float value to an integer register and back. */
		681
		682	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		683
		684	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		685
		686	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		687
		688	The reverse operation of the previos function - takes the bit representation
		689	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		690	or C<double> format.
		691
		692	This function should work even when the native floating point format isn't
		693	IEEE compliant, of course at a speed and code size penalty, and of course
		694	also within reasonable limits (it tries to convert normals and denormals,
		695	and might be lucky for infinities, and with extraordinary luck, also for
		696	negative zero).
		697
		698	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		699	be able to optimise away this function completely.
434		700
435	=back	701	=back
436		702
437	=head2 ARITHMETIC	703	=head2 ARITHMETIC
438		704
…		…
448	C<ecb_mod> implements the mathematical modulo operation, which is missing	714	C<ecb_mod> implements the mathematical modulo operation, which is missing
449	in the language.	715	in the language.
450		716
451	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be	717	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
452	negatable, that is, both C<m> and C<-m> must be representable in its	718	negatable, that is, both C<m> and C<-m> must be representable in its
453	type (this typically includes the minimum signed integer value, the same	719	type (this typically excludes the minimum signed integer value, the same
454	limitation as for C</> and C<%> in C).	720	limitation as for C</> and C<%> in C).
455		721
456	Current GCC versions compile this into an efficient branchless sequence on	722	Current GCC versions compile this into an efficient branchless sequence on
457	many systems.	723	almost all CPUs.
458		724
459	For example, when you want to rotate forward through the members of an	725	For example, when you want to rotate forward through the members of an
460	array for increasing C<m> (which might be negative), then you should use	726	array for increasing C<m> (which might be negative), then you should use
461	C<ecb_mod>, as the C<%> operator might give either negative results, or	727	C<ecb_mod>, as the C<%> operator might give either negative results, or
462	change direction for negative values:	728	change direction for negative values:
463		729
464	for (m = -100; m <= 100; ++m)	730	for (m = -100; m <= 100; ++m)
465	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];	731	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
466		732
		733	=item x = ecb_div_rd (val, div)
		734
		735	=item x = ecb_div_ru (val, div)
		736
		737	Returns C<val> divided by C<div> rounded down or up, respectively.
		738	C<val> and C<div> must have integer types and C<div> must be strictly
		739	positive. Note that these functions are implemented with macros in C
		740	and with function templates in C++.
		741
467	=back	742	=back
468		743
469	=head2 UTILITY	744	=head2 UTILITY
470		745
471	=over 4	746	=over 4
…		…
480	for (i = 0; i < ecb_array_length (primes); i++)	755	for (i = 0; i < ecb_array_length (primes); i++)
481	sum += primes [i];	756	sum += primes [i];
482		757
483	=back	758	=back
484		759
		760	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
485		761
		762	These symbols need to be defined before including F<ecb.h> the first time.
		763
		764	=over 4
		765
		766	=item ECB_NO_THREADS
		767
		768	If F<ecb.h> is never used from multiple threads, then this symbol can
		769	be defined, in which case memory fences (and similar constructs) are
		770	completely removed, leading to more efficient code and fewer dependencies.
		771
		772	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		773
		774	=item ECB_NO_SMP
		775
		776	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		777	multiple threads, but never concurrently (e.g. if the system the program
		778	runs on has only a single CPU with a single core, no hyperthreading and so
		779	on), then this symbol can be defined, leading to more efficient code and
		780	fewer dependencies.
		781
		782	=item ECB_NO_LIBM
		783
		784	When defined to C<1>, do not export any functions that might introduce
		785	dependencies on the math library (usually called F<-lm>) - these are
		786	marked with [-UECB_NO_LIBM].
		787
		788	=back
		789
		790

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Comparing cvsroot/libecb/ecb.pod (file contents): Revision 1.27 by root, Wed Jun 1 01:29:36 2011 UTC vs. Revision 1.54 by root, Wed Dec 19 23:33:47 2012 UTC

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Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.27 by root, Wed Jun 1 01:29:36 2011 UTC vs.
Revision 1.54 by root, Wed Dec 19 23:33:47 2012 UTC