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

Comparing libecb/ecb.pod (file contents):
Revision 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs.
Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 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
		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
58	=head2 GCC ATTRIBUTES	168	=head2 ATTRIBUTES
59		169
60	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
61	attributes that you cna assign to functions, variables and sometimes even	171	assigned to functions, variables and sometimes even types - much like
62	types - much like C<const> or C<volatile> in C.	172	C<const> or C<volatile> in C. They are implemented using either GCC
63		173	attributes or other compiler/language specific features. Attributes
64	While GCC allows declarations to show up in many surprising places,
65	but not in many expeted places, the safest way is to put attribute
66	declarations before the whole declaration:	174	declarations must be put before the whole declaration:
67		175
68	ecb_const int mysqrt (int a);	176	ecb_const int mysqrt (int a);
69	ecb_unused int i;	177	ecb_unused int i;
70		178
71	For variables, it is often nicer to put the attribute after the name, and
72	avoid multiple declarations using commas:
73
74	int i ecb_unused;
75
76	=over 4	179	=over 4
77
78	=item ecb_attribute ((attrs...))
79
80	A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
81	nothing on other compilers, so the effect is that only GCC sees these.
82
83	Example: use the C<deprecated> attribute on a function.
84
85	ecb_attribute((__deprecated__)) void
86	do_not_use_me_anymore (void);
87		180
88	=item ecb_unused	181	=item ecb_unused
89		182
90	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
91	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.
92	declare a variable but do not always use it:	185	declare a variable but do not always use it:
93		186
94	{	187	{
95	int var ecb_unused;	188	ecb_unused int var;
96		189
97	#ifdef SOMECONDITION	190	#ifdef SOMECONDITION
98	var = ...;	191	var = ...;
99	return var;	192	return var;
100	#else	193	#else
101	return 0;	194	return 0;
102	#endif	195	#endif
103	}	196	}
104		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
105	=item ecb_noinline	217	=item ecb_noinline
106		218
107	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
108	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
109	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.
…		…
122	}	234	}
123		235
124	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
125	its own, so this is mainly useful for declarations.	237	its own, so this is mainly useful for declarations.
126		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
127	=item ecb_const	260	=item ecb_const
128		261
129	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,
130	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
131	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
…		…
183		316
184	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
185	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
186	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
187	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
188	C<ecb_unlikely> had been used to reach them.	321	C<ecb_expect_false> had been used to reach them.
189		322
190	Good examples for such functions would be error reporting functions, or	323	Good examples for such functions would be error reporting functions, or
191	functions only called in exceptional or rare cases.	324	functions only called in exceptional or rare cases.
192		325
193	=item ecb_artificial	326	=item ecb_artificial
194		327
195	Declares the function as "artificial", in this case meaning that this	328	Declares the function as "artificial", in this case meaning that this
196	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
197	- 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
198	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
199	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.
200		333
201	Marking them as artificial will instruct the debugger about just this,	334	Marking them as artificial will instruct the debugger about just this,
…		…
221		354
222	=head2 OPTIMISATION HINTS	355	=head2 OPTIMISATION HINTS
223		356
224	=over 4	357	=over 4
225		358
226	=item bool ecb_is_constant(expr)	359	=item bool ecb_is_constant (expr)
227		360
228	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
229	constant, and false otherwise.	362	constant, and false otherwise.
230		363
231	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
…		…
255		388
256	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
257	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
258	branch optimisations.	391	branch optimisations.
259		392
260	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
261	C<ecb_unlikely> functions instead.	394	C<ecb_expect_false> functions instead.
262		395
		396	=item bool ecb_expect_true (cond)
		397
263	=item bool ecb_likely (cond)	398	=item bool ecb_expect_false (cond)
264
265	=item bool ecb_unlikely (cond)
266		399
267	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
268	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
269	other conditional statement, it will not change the program:	402	other conditional statement, it will not change the program:
270		403
271	/* these two do the same thing */	404	/* these two do the same thing */
272	if (some_condition) ...;	405	if (some_condition) ...;
273	if (ecb_likely (some_condition)) ...;	406	if (ecb_expect_true (some_condition)) ...;
274		407
275	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
276	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
277	true).	410	unlikely to be true).
278		411
279	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
280	rare, exceptional, case, then use C<ecb_unlikely>:	413	rare, exceptional, case, then use C<ecb_expect_false>:
281		414
282	void my_free (void *ptr)	415	void my_free (void *ptr)
283	{	416	{
284	if (ecb_unlikely (ptr == 0))	417	if (ecb_expect_false (ptr == 0))
285	return;	418	return;
286	}	419	}
287		420
288	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
289	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
290	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.
291		430
292	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
293	memory block (for example, inside an implementation of a string stream) -	432	memory block (for example, inside an implementation of a string stream) -
294	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
295	you expect that most checks will turn out to be false:	434	you expect that most checks will turn out to be false:
296		435
297	/* make sure we have "size" extra room in our buffer */	436	/* make sure we have "size" extra room in our buffer */
298	ecb_inline void	437	ecb_inline void
299	reserve (int size)	438	reserve (int size)
300	{	439	{
301	if (ecb_unlikely (current + size > end))	440	if (ecb_expect_false (current + size > end))
302	real_reserve_method (size); /* presumably noinline */	441	real_reserve_method (size); /* presumably noinline */
303	}	442	}
304		443
305	=item bool ecb_assume (cond)	444	=item bool ecb_assume (cond)
306		445
…		…
309		448
310	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
311	conditions that might improve code generation, but which are impossible to	450	conditions that might improve code generation, but which are impossible to
312	deduce form the code itself.	451	deduce form the code itself.
313		452
314	For example, the example reservation function from the C<ecb_unlikely>	453	For example, the example reservation function from the C<ecb_expect_false>
315	description could be written thus (only C<ecb_assume> was added):	454	description could be written thus (only C<ecb_assume> was added):
316		455
317	ecb_inline void	456	ecb_inline void
318	reserve (int size)	457	reserve (int size)
319	{	458	{
320	if (ecb_unlikely (current + size > end))	459	if (ecb_expect_false (current + size > end))
321	real_reserve_method (size); /* presumably noinline */	460	real_reserve_method (size); /* presumably noinline */
322		461
323	ecb_assume (current + size <= end);	462	ecb_assume (current + size <= end);
324	}	463	}
325		464
…		…
374	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
375	cache.	514	cache.
376		515
377	=back	516	=back
378		517
379	=head2 BIT FIDDLING / BITSTUFFS	518	=head2 BIT FIDDLING / BIT WIZARDRY
380		519
381	=over 4	520	=over 4
382		521
383	=item bool ecb_big_endian ()	522	=item bool ecb_big_endian ()
384		523
…		…
386		525
387	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
388	(most-significant byte first) or little endian (least-significant byte	527	(most-significant byte first) or little endian (least-significant byte
389	first) respectively.	528	first) respectively.
390		529
		530	On systems that are neither, their return values are unspecified.
		531
391	=item int ecb_ctz32 (uint32_t x)	532	=item int ecb_ctz32 (uint32_t x)
392		533
		534	=item int ecb_ctz64 (uint64_t x)
		535
393	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
394	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
395	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.
396	common use case is to compute the integer binary logarithm, i.e.,	539
397	floor(log2(n)). For example:	540	For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
		541
		542	For example:
398		543
399	ecb_ctz32 (3) = 0	544	ecb_ctz32 (3) = 0
400	ecb_ctz32 (6) = 1	545	ecb_ctz32 (6) = 1
401		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
402	=item int ecb_popcount32 (uint32_t x)	572	=item int ecb_popcount32 (uint32_t x)
403		573
		574	=item int ecb_popcount64 (uint64_t x)
		575
404	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:
405		581
406	ecb_popcount32 (7) = 3	582	ecb_popcount32 (7) = 3
407	ecb_popcount32 (255) = 8	583	ecb_popcount32 (255) = 8
408		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
409	=item uint32_t ecb_bswap16 (uint32_t x)	599	=item uint32_t ecb_bswap16 (uint32_t x)
410		600
411	=item uint32_t ecb_bswap32 (uint32_t x)	601	=item uint32_t ecb_bswap32 (uint32_t x)
412		602
		603	=item uint64_t ecb_bswap64 (uint64_t x)
		604
413	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
414	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)
415		620
416	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)	621	=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
417		622
418	=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)	623	=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
419		624
420	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
421	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>).
422		628
423	Current GCC versions understand these functions and usually compile them	629	Current GCC versions understand these functions and usually compile them
424	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).
425		632
426	=back	633	=back
427		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
428	=head2 ARITHMETIC	692	=head2 ARITHMETIC
429		693
430	=over 4	694	=over 4
431		695
432	=item x = ecb_mod (m, n)	696	=item x = ecb_mod (m, n)
433		697
434	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
435	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
436	return value is always positive - ISO C guarantees very little when	701	the return value is always positive and that the two numbers I<m> and
437	negative numbers are used with C<%>.	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.
438		705
439	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
440	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
441	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++.
442		730
443	=back	731	=back
444		732
445	=head2 UTILITY	733	=head2 UTILITY
446		734
…		…
456	for (i = 0; i < ecb_array_length (primes); i++)	744	for (i = 0; i < ecb_array_length (primes); i++)
457	sum += primes [i];	745	sum += primes [i];
458		746
459	=back	747	=back
460		748
		749	=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
461		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 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs. Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC

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Comparing libecb/ecb.pod (file contents):
Revision 1.23 by sf-exg, Fri May 27 01:35:46 2011 UTC vs.
Revision 1.61 by sf-exg, Thu Feb 12 12:37:33 2015 UTC