[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 1.50 by root, Thu Jun 28 20:20:27 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	=back
58		156
59	=head2 GCC ATTRIBUTES	157	=head2 GCC ATTRIBUTES
60		158
61	A major part of libecb deals with GCC attributes. These are additional	159	A major part of libecb deals with GCC attributes. These are additional
62	attributes that you can assign to functions, variables and sometimes even	160	attributes that you can assign to functions, variables and sometimes even
…		…
101	#else	199	#else
102	return 0;	200	return 0;
103	#endif	201	#endif
104	}	202	}
105		203
		204	=item ecb_inline
		205
		206	This is not actually an attribute, but you use it like one. It expands
		207	either to C<static inline> or to just C<static>, if inline isn't
		208	supported. It should be used to declare functions that should be inlined,
		209	for code size or speed reasons.
		210
		211	Example: inline this function, it surely will reduce codesize.
		212
		213	ecb_inline int
		214	negmul (int a, int b)
		215	{
		216	return - (a * b);
		217	}
		218
106	=item ecb_noinline	219	=item ecb_noinline
107		220
108	Prevent a function from being inlined - it might be optimised away, but	221	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	222	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.	223	is rarely called and large enough for inlining not to be helpful.
…		…
381	After processing the node, (part of) the next node might already be in	494	After processing the node, (part of) the next node might already be in
382	cache.	495	cache.
383		496
384	=back	497	=back
385		498
386	=head2 BIT FIDDLING / BITSTUFFS	499	=head2 BIT FIDDLING / BIT WIZARDRY
387		500
388	=over 4	501	=over 4
389		502
390	=item bool ecb_big_endian ()	503	=item bool ecb_big_endian ()
391		504
…		…
397		510
398	On systems that are neither, their return values are unspecified.	511	On systems that are neither, their return values are unspecified.
399		512
400	=item int ecb_ctz32 (uint32_t x)	513	=item int ecb_ctz32 (uint32_t x)
401		514
		515	=item int ecb_ctz64 (uint64_t x)
		516
402	Returns the index of the least significant bit set in C<x> (or	517	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	518	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	519	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	520
		521	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		522
406	(n))>. For example:	523	For example:
407		524
408	ecb_ctz32 (3) = 0	525	ecb_ctz32 (3) = 0
409	ecb_ctz32 (6) = 1	526	ecb_ctz32 (6) = 1
410		527
		528	=item bool ecb_is_pot32 (uint32_t x)
		529
		530	=item bool ecb_is_pot64 (uint32_t x)
		531
		532	Return true iff C<x> is a power of two or C<x == 0>.
		533
		534	For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
		535
		536	=item int ecb_ld32 (uint32_t x)
		537
		538	=item int ecb_ld64 (uint64_t x)
		539
		540	Returns the index of the most significant bit set in C<x>, or the number
		541	of digits the number requires in binary (so that C<< 2**ld <= x <
		542	2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
		543	to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
		544	example to see how many bits a certain number requires to be encoded.
		545
		546	This function is similar to the "count leading zero bits" function, except
		547	that that one returns how many zero bits are "in front" of the number (in
		548	the given data type), while C<ecb_ld> returns how many bits the number
		549	itself requires.
		550
		551	For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
		552
411	=item int ecb_popcount32 (uint32_t x)	553	=item int ecb_popcount32 (uint32_t x)
412		554
		555	=item int ecb_popcount64 (uint64_t x)
		556
413	Returns the number of bits set to 1 in C<x>. For example:	557	Returns the number of bits set to 1 in C<x>.
		558
		559	For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
		560
		561	For example:
414		562
415	ecb_popcount32 (7) = 3	563	ecb_popcount32 (7) = 3
416	ecb_popcount32 (255) = 8	564	ecb_popcount32 (255) = 8
417		565
		566	=item uint8_t ecb_bitrev8 (uint8_t x)
		567
		568	=item uint16_t ecb_bitrev16 (uint16_t x)
		569
		570	=item uint32_t ecb_bitrev32 (uint32_t x)
		571
		572	Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
		573	and so on.
		574
		575	Example:
		576
		577	ecb_bitrev8 (0xa7) = 0xea
		578	ecb_bitrev32 (0xffcc4411) = 0x882233ff
		579
418	=item uint32_t ecb_bswap16 (uint32_t x)	580	=item uint32_t ecb_bswap16 (uint32_t x)
419		581
420	=item uint32_t ecb_bswap32 (uint32_t x)	582	=item uint32_t ecb_bswap32 (uint32_t x)
421		583
		584	=item uint64_t ecb_bswap64 (uint64_t x)
		585
422	These two functions return the value of the 16-bit (32-bit) value C<x>	586	These functions return the value of the 16-bit (32-bit, 64-bit) value
423	after reversing the order of bytes (0x11223344 becomes 0x44332211).	587	C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
		588	C<ecb_bswap32>).
		589
		590	=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
		591
		592	=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
		593
		594	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
		595
		596	=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
		597
		598	=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
		599
		600	=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
424		601
425	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	602	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
426		603
427	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	604	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
428		605
429	These two functions return the value of C<x> after rotating all the bits	606	These two families of functions return the value of C<x> after rotating
430	by C<count> positions to the right or left respectively.	607	all the bits by C<count> positions to the right (C<ecb_rotr>) or left
		608	(C<ecb_rotl>).
431		609
432	Current GCC versions understand these functions and usually compile them	610	Current GCC versions understand these functions and usually compile them
433	to "optimal" code (e.g. a single C<roll> on x86).	611	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		612	x86).
		613
		614	=back
		615
		616	=head2 FLOATING POINT FIDDLING
		617
		618	=over 4
		619
		620	=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
		621
		622	=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
		623
		624	These functions each take an argument in the native C<float> or C<double>
		625	type and return the IEEE 754 bit representation of it.
		626
		627	The bit representation is just as IEEE 754 defines it, i.e. the sign bit
		628	will be the most significant bit, followed by exponent and mantissa.
		629
		630	This function should work even when the native floating point format isn't
		631	IEEE compliant, of course at a speed and code size penalty, and of course
		632	also within reasonable limits (it tries to convert NaNs, infinities and
		633	denormals, but will likely convert negative zero to positive zero).
		634
		635	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		636	be able to optimise away this function completely.
		637
		638	These functions can be helpful when serialising floats to the network - you
		639	can serialise the return value like a normal uint32_t/uint64_t.
		640
		641	Another use for these functions is to manipulate floating point values
		642	directly.
		643
		644	Silly example: toggle the sign bit of a float.
		645
		646	/* On gcc-4.7 on amd64, */
		647	/* this results in a single add instruction to toggle the bit, and 4 extra */
		648	/* instructions to move the float value to an integer register and back. */
		649
		650	x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
		651
		652	=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
		653
		654	=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM]
		655
		656	The reverse operation of the previos function - takes the bit representation
		657	of an IEEE binary32 or binary64 number and converts it to the native C<float>
		658	or C<double> format.
		659
		660	This function should work even when the native floating point format isn't
		661	IEEE compliant, of course at a speed and code size penalty, and of course
		662	also within reasonable limits (it tries to convert normals and denormals,
		663	and might be lucky for infinities, and with extraordinary luck, also for
		664	negative zero).
		665
		666	On all modern platforms (where C<ECB_STDFP> is true), the compiler should
		667	be able to optimise away this function completely.
434		668
435	=back	669	=back
436		670
437	=head2 ARITHMETIC	671	=head2 ARITHMETIC
438		672
…		…
448	C<ecb_mod> implements the mathematical modulo operation, which is missing	682	C<ecb_mod> implements the mathematical modulo operation, which is missing
449	in the language.	683	in the language.
450		684
451	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be	685	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	686	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	687	type (this typically excludes the minimum signed integer value, the same
454	limitation as for C</> and C<%> in C).	688	limitation as for C</> and C<%> in C).
455		689
456	Current GCC versions compile this into an efficient branchless sequence on	690	Current GCC versions compile this into an efficient branchless sequence on
457	many systems.	691	almost all CPUs.
458		692
459	For example, when you want to rotate forward through the members of an	693	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	694	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	695	C<ecb_mod>, as the C<%> operator might give either negative results, or
462	change direction for negative values:	696	change direction for negative values:
463		697
464	for (m = -100; m <= 100; ++m)	698	for (m = -100; m <= 100; ++m)
465	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];	699	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
466		700
		701	=item x = ecb_div_rd (val, div)
		702
		703	=item x = ecb_div_ru (val, div)
		704
		705	Returns C<val> divided by C<div> rounded down or up, respectively.
		706	C<val> and C<div> must have integer types and C<div> must be strictly
		707	positive. Note that these functions are implemented with macros in C
		708	and with function templates in C++.
		709
467	=back	710	=back
468		711
469	=head2 UTILITY	712	=head2 UTILITY
470		713
471	=over 4	714	=over 4
…		…
480	for (i = 0; i < ecb_array_length (primes); i++)	723	for (i = 0; i < ecb_array_length (primes); i++)
481	sum += primes [i];	724	sum += primes [i];
482		725
483	=back	726	=back
484		727
		728	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
485		729
		730	These symbols need to be defined before including F<ecb.h> the first time.
		731
		732	=over 4
		733
		734	=item ECB_NO_THRADS
		735
		736	If F<ecb.h> is never used from multiple threads, then this symbol can
		737	be defined, in which case memory fences (and similar constructs) are
		738	completely removed, leading to more efficient code and fewer dependencies.
		739
		740	Setting this symbol to a true value implies C<ECB_NO_SMP>.
		741
		742	=item ECB_NO_SMP
		743
		744	The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
		745	multiple threads, but never concurrently (e.g. if the system the program
		746	runs on has only a single CPU with a single core, no hyperthreading and so
		747	on), then this symbol can be defined, leading to more efficient code and
		748	fewer dependencies.
		749
		750	=item ECB_NO_LIBM
		751
		752	When defined to C<1>, do not export any functions that might introduce
		753	dependencies on the math library (usually called F<-lm>) - these are
		754	marked with [-UECB_NO_LIBM].
		755
		756	=back
		757
		758

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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 1.50 by root, Thu Jun 28 20:20:27 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 1.50 by root, Thu Jun 28 20:20:27 2012 UTC