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

Comparing libecb/ecb.pod (file contents):
Revision 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC

…		…
15	It mainly provides a number of wrappers around GCC built-ins, together	15	It mainly provides a number of wrappers around GCC built-ins, together
16	with replacement functions for other compilers. In addition to this,	16	with replacement functions for other compilers. In addition to this,
17	it provides a number of other lowlevel C utilities, such as endianness	17	it provides a number of other lowlevel C utilities, such as endianness
18	detection, byte swapping or bit rotations.	18	detection, byte swapping or bit rotations.
19		19
20	Or in other words, things that should be built-in into any standard C	20	Or in other words, things that should be built into any standard C system,
21	system, but aren't.	21	but aren't, implemented as efficient as possible with GCC, and still
		22	correct with other compilers.
22		23
23	More might come.	24	More might come.
24		25
25	=head2 ABOUT THE HEADER	26	=head2 ABOUT THE HEADER
26		27
…		…
53	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
54	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
55	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
56	refers to any kind of boolean value, not a specific type.	57	refers to any kind of boolean value, not a specific type.
57		58
58	=head2 GCC ATTRIBUTES	59	=head2 TYPES / TYPE SUPPORT
59		60
60	blabla where to put, what others	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).
61		78
62	=over 4	79	=over 4
63		80
64	=item ecb_attribute ((attrs...))	81	=item ECB_C
65		82
66	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to	83	True if the implementation defines the C<__STDC__> macro to a true value,
67	nothing on other compilers, so the effect is that only GCC sees these.	84	while not claiming to be C++.
68		85
69	Example: use the C<deprecated> attribute on a function.	86	=item ECB_C99
70		87
71	ecb_attribute((__deprecated__)) void	88	True if the implementation claims to be compliant to C99 (ISO/IEC
72	do_not_use_me_anymore (void);	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 ATTRIBUTES
		169
		170	A major part of libecb deals with additional attributes that can be
		171	assigned to functions, variables and sometimes even types - much like
		172	C<const> or C<volatile> in C. They are implemented using either GCC
		173	attributes or other compiler/language specific features. Attributes
		174	declarations must be put before the whole declaration:
		175
		176	ecb_const int mysqrt (int a);
		177	ecb_unused int i;
		178
		179	=over 4
73		180
74	=item ecb_unused	181	=item ecb_unused
75		182
76	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
77	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.
…		…
86	#else	193	#else
87	return 0;	194	return 0;
88	#endif	195	#endif
89	}	196	}
90		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
		203	=item ecb_inline
		204
		205	Expands either to C<static inline> or to just C<static>, if inline
		206	isn't supported. It should be used to declare functions that should be
		207	inlined, for code size or speed reasons.
		208
		209	Example: inline this function, it surely will reduce codesize.
		210
		211	ecb_inline int
		212	negmul (int a, int b)
		213	{
		214	return - (a * b);
		215	}
		216
91	=item ecb_noinline	217	=item ecb_noinline
92		218
93	Prevent a function from being inlined - it might be optimised away, but	219	Prevent a function from being inlined - it might be optimised away, but
94	not inlined into other functions. This is useful if you know your function	220	not inlined into other functions. This is useful if you know your function
95	is rarely called and large enough for inlining not to be helpful.	221	is rarely called and large enough for inlining not to be helpful.
…		…
105	{	231	{
106	puts (errline);	232	puts (errline);
107	abort ();	233	abort ();
108	}	234	}
109		235
110	In this case, the compiler would probbaly be smart enough to decude it on	236	In this case, the compiler would probably be smart enough to deduce it on
111	it's own, so this is mainly useful for declarations.	237	its own, so this is mainly useful for declarations.
		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	}
112		259
113	=item ecb_const	260	=item ecb_const
114		261
115	Declares that the function only depends on the values of it's arguments,	262	Declares that the function only depends on the values of its arguments,
116	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
117	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
118	non-const functions. It also must not have any side effects.	265	non-const functions. It also must not have any side effects.
119		266
120	Such a function can be optimised much more aggressively by the compiler -	267	Such a function can be optimised much more aggressively by the compiler -
121	for example, multiple calls with the same arguments can be optimised into	268	for example, multiple calls with the same arguments can be optimised into
122	a single call, which wouldn't be possible if the compiler would have to	269	a single call, which wouldn't be possible if the compiler would have to
123	expect any side effects.	270	expect any side effects.
124		271
125	It is best suited for functions in the sense of mathematical functions,	272	It is best suited for functions in the sense of mathematical functions,
126	such as a function return the square root of its input argument.	273	such as a function returning the square root of its input argument.
127		274
128	Not suited would be a function that calculates the hash of some memory	275	Not suited would be a function that calculates the hash of some memory
129	area you pass in, prints some messages or looks at a global variable to	276	area you pass in, prints some messages or looks at a global variable to
130	decide on rounding.	277	decide on rounding.
131		278
…		…
154	possible.	301	possible.
155		302
156	The compiler reacts by trying to place hot functions near to each other in	303	The compiler reacts by trying to place hot functions near to each other in
157	memory.	304	memory.
158		305
159	Whether a function is hot or not often depend son the whole program,	306	Whether a function is hot or not often depends on the whole program,
160	and less on the function itself. C<ecb_cold> is likely more useful in	307	and less on the function itself. C<ecb_cold> is likely more useful in
161	practise.	308	practise.
162		309
163	=item ecb_cold	310	=item ecb_cold
164		311
…		…
169		316
170	In addition to placing cold functions together (or at least away from hot	317	In addition to placing cold functions together (or at least away from hot
171	functions), this knowledge can be used in other ways, for example, the	318	functions), this knowledge can be used in other ways, for example, the
172	function will be optimised for size, as opposed to speed, and codepaths	319	function will be optimised for size, as opposed to speed, and codepaths
173	leading to calls to those functions can automatically be marked as if	320	leading to calls to those functions can automatically be marked as if
174	C<ecb_unlikel> had been used to reach them.	321	C<ecb_expect_false> had been used to reach them.
175		322
176	Good examples for such functions would be error reporting functions, or	323	Good examples for such functions would be error reporting functions, or
177	functions only called in exceptional or rare cases.	324	functions only called in exceptional or rare cases.
178		325
179	=item ecb_artificial	326	=item ecb_artificial
180		327
181	Declares the function as "artificial", in this case meaning that this	328	Declares the function as "artificial", in this case meaning that this
182	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
183	- 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
184	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
185	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.
186		333
187	Marking them as artificial will instruct the debugger about just this,	334	Marking them as artificial will instruct the debugger about just this,
…		…
207		354
208	=head2 OPTIMISATION HINTS	355	=head2 OPTIMISATION HINTS
209		356
210	=over 4	357	=over 4
211		358
212	=item bool ecb_is_constant(expr)	359	=item bool ecb_is_constant (expr)
213		360
214	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
215	constant, and false otherwise.	362	constant, and false otherwise.
216		363
217	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
…		…
241		388
242	Evaluates C<expr> and returns it. In addition, it tells the compiler that	389	Evaluates C<expr> and returns it. In addition, it tells the compiler that
243	the C<expr> evaluates to C<value> a lot, which can be used for static	390	the C<expr> evaluates to C<value> a lot, which can be used for static
244	branch optimisations.	391	branch optimisations.
245		392
246	Usually, you want to use the more intuitive C<ecb_likely> and	393	Usually, you want to use the more intuitive C<ecb_expect_true> and
247	C<ecb_unlikely> functions instead.	394	C<ecb_expect_false> functions instead.
248		395
		396	=item bool ecb_expect_true (cond)
		397
249	=item bool ecb_likely (cond)	398	=item bool ecb_expect_false (cond)
250
251	=item bool ecb_unlikely (cond)
252		399
253	These two functions expect a expression that is true or false and return	400	These two functions expect a expression that is true or false and return
254	C<1> or C<0>, respectively, so when used in the condition of an C<if> or	401	C<1> or C<0>, respectively, so when used in the condition of an C<if> or
255	other conditional statement, it will not change the program:	402	other conditional statement, it will not change the program:
256		403
257	/* these two do the same thing */	404	/* these two do the same thing */
258	if (some_condition) ...;	405	if (some_condition) ...;
259	if (ecb_likely (some_condition)) ...;	406	if (ecb_expect_true (some_condition)) ...;
260		407
261	However, by using C<ecb_likely>, you tell the compiler that the condition	408	However, by using C<ecb_expect_true>, you tell the compiler that the
262	is likely to be true (and for C<ecb_unlikely>, that it is unlikely to be	409	condition is likely to be true (and for C<ecb_expect_false>, that it is
263	true).	410	unlikely to be true).
264		411
265	For example, when you check for a null pointer and expect this to be a	412	For example, when you check for a null pointer and expect this to be a
266	rare, exceptional, case, then use C<ecb_unlikely>:	413	rare, exceptional, case, then use C<ecb_expect_false>:
267		414
268	void my_free (void *ptr)	415	void my_free (void *ptr)
269	{	416	{
270	if (ecb_unlikely (ptr == 0))	417	if (ecb_expect_false (ptr == 0))
271	return;	418	return;
272	}	419	}
273		420
274	Consequent use of these functions to mark away exceptional cases or to	421	Consequent use of these functions to mark away exceptional cases or to
275	tell the compiler what the hot path through a function is can increase	422	tell the compiler what the hot path through a function is can increase
276	performance considerably.	423	performance considerably.
		424
		425	You might know these functions under the name C<likely> and C<unlikely>
		426	- while these are common aliases, we find that the expect name is easier
		427	to understand when quickly skimming code. If you wish, you can use
		428	C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of
		429	C<ecb_expect_false> - these are simply aliases.
277		430
278	A very good example is in a function that reserves more space for some	431	A very good example is in a function that reserves more space for some
279	memory block (for example, inside an implementation of a string stream) -	432	memory block (for example, inside an implementation of a string stream) -
280	each time something is added, you have to check for a buffer overrun, but	433	each time something is added, you have to check for a buffer overrun, but
281	you expect that most checks will turn out to be false:	434	you expect that most checks will turn out to be false:
282		435
283	/* make sure we have "size" extra room in our buffer */	436	/* make sure we have "size" extra room in our buffer */
284	ecb_inline void	437	ecb_inline void
285	reserve (int size)	438	reserve (int size)
286	{	439	{
287	if (ecb_unlikely (current + size > end))	440	if (ecb_expect_false (current + size > end))
288	real_reserve_method (size); /* presumably noinline */	441	real_reserve_method (size); /* presumably noinline */
289	}	442	}
290		443
291	=item bool ecb_assume (cond)	444	=item bool ecb_assume (cond)
292		445
…		…
295		448
296	This can be used to teach the compiler about invariants or other	449	This can be used to teach the compiler about invariants or other
297	conditions that might improve code generation, but which are impossible to	450	conditions that might improve code generation, but which are impossible to
298	deduce form the code itself.	451	deduce form the code itself.
299		452
300	For example, the example reservation function from the C<ecb_unlikely>	453	For example, the example reservation function from the C<ecb_expect_false>
301	description could be written thus (only C<ecb_assume> was added):	454	description could be written thus (only C<ecb_assume> was added):
302		455
303	ecb_inline void	456	ecb_inline void
304	reserve (int size)	457	reserve (int size)
305	{	458	{
306	if (ecb_unlikely (current + size > end))	459	if (ecb_expect_false (current + size > end))
307	real_reserve_method (size); /* presumably noinline */	460	real_reserve_method (size); /* presumably noinline */
308		461
309	ecb_assume (current + size <= end);	462	ecb_assume (current + size <= end);
310	}	463	}
311		464
…		…
360	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
361	cache.	514	cache.
362		515
363	=back	516	=back
364		517
365	=head2 BIT FIDDLING / BITSTUFFS	518	=head2 BIT FIDDLING / BIT WIZARDRY
366		519
367	=over 4	520	=over 4
368		521
369	=item bool ecb_big_endian ()	522	=item bool ecb_big_endian ()
370		523
…		…
372		525
373	These two functions return true if the byte order is big endian	526	These two functions return true if the byte order is big endian
374	(most-significant byte first) or little endian (least-significant byte	527	(most-significant byte first) or little endian (least-significant byte
375	first) respectively.	528	first) respectively.
376		529
		530	On systems that are neither, their return values are unspecified.
		531
377	=item int ecb_ctz32 (uint32_t x)	532	=item int ecb_ctz32 (uint32_t x)
378		533
		534	=item int ecb_ctz64 (uint64_t x)
		535
379	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
380	equivalently the number of bits set to 0 before the least significant	537	equivalently the number of bits set to 0 before the least significant bit
381	bit set), starting from 0. If C<x> is 0 the result is undefined. A	538	set), starting from 0. If C<x> is 0 the result is undefined.
382	common use case is to compute the integer binary logarithm, i.e.,	539
383	floor(log2(n)). For example:	540	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		541
		542	For example:
384		543
385	ecb_ctz32 (3) = 0	544	ecb_ctz32 (3) = 0
386	ecb_ctz32 (6) = 1	545	ecb_ctz32 (6) = 1
387		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
388	=item int ecb_popcount32 (uint32_t x)	572	=item int ecb_popcount32 (uint32_t x)
389		573
		574	=item int ecb_popcount64 (uint64_t x)
		575
390	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:
391		581
392	ecb_popcount32 (7) = 3	582	ecb_popcount32 (7) = 3
393	ecb_popcount32 (255) = 8	583	ecb_popcount32 (255) = 8
394		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
395	=item uint32_t ecb_bswap16 (uint32_t x)	599	=item uint32_t ecb_bswap16 (uint32_t x)
396		600
397	=item uint32_t ecb_bswap32 (uint32_t x)	601	=item uint32_t ecb_bswap32 (uint32_t x)
398		602
		603	=item uint64_t ecb_bswap64 (uint64_t x)
		604
399	These two functions return the value of the 16-bit (32-bit) variable	605	These functions return the value of the 16-bit (32-bit, 64-bit) value
400	C<x> after reversing the order of bytes.	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)
401		620
402	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	621	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
403		622
404	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	623	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
405		624
406	These two functions return the value of C<x> after shifting all the bits	625	These two families of functions return the value of C<x> after rotating
407	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>).
		628
		629	Current GCC versions understand these functions and usually compile them
		630	to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
		631	x86).
408		632
409	=back	633	=back
410		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
411	=head2 ARITHMETIC	692	=head2 ARITHMETIC
412		693
413	=over 4	694	=over 4
414		695
415	=item x = ecb_mod (m, n)	696	=item x = ecb_mod (m, n)
416		697
417	Returns the positive remainder of the modulo operation between C<m> and	698	Returns C<m> modulo C<n>, which is the same as the positive remainder
		699	of the division operation between C<m> and C<n>, using floored
418	C<n>. Unlike the C modulo operator C<%>, this function ensures that the	700	division. Unlike the C remainder operator C<%>, this function ensures that
419	return value is always positive).	701	the return value is always positive and that the two numbers I<m> and
		702	I<m' = m + i * n> result in the same value modulo I<n> - in other words,
		703	C<ecb_mod> implements the mathematical modulo operation, which is missing
		704	in the language.
420		705
421	C<n> must be strictly positive (i.e. C<< >1 >>), while C<m> must be	706	C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
422	negatable, that is, both C<m> and C<-m> must be representable in its	707	negatable, that is, both C<m> and C<-m> must be representable in its
423	type.	708	type (this typically excludes the minimum signed integer value, the same
		709	limitation as for C</> and C<%> in C).
		710
		711	Current GCC versions compile this into an efficient branchless sequence on
		712	almost all CPUs.
		713
		714	For example, when you want to rotate forward through the members of an
		715	array for increasing C<m> (which might be negative), then you should use
		716	C<ecb_mod>, as the C<%> operator might give either negative results, or
		717	change direction for negative values:
		718
		719	for (m = -100; m <= 100; ++m)
		720	int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
		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++.
424		730
425	=back	731	=back
426		732
427	=head2 UTILITY	733	=head2 UTILITY
428		734
429	=over 4	735	=over 4
430		736
431	=item element_count = ecb_array_length (name) [MACRO]	737	=item element_count = ecb_array_length (name)
432		738
433	Returns the number of elements in the array C<name>. For example:	739	Returns the number of elements in the array C<name>. For example:
434		740
435	int primes[] = { 2, 3, 5, 7, 11 };	741	int primes[] = { 2, 3, 5, 7, 11 };
436	int sum = 0;	742	int sum = 0;
…		…
438	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
439	sum += primes [i];	745	sum += primes [i];
440		746
441	=back	747	=back
442		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
443		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 1.18 by root, Fri May 27 00:01:28 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 1.18 by root, Fri May 27 00:01:28 2011 UTC vs.
Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC