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Revision 1.37 by sf-exg, Wed Aug 24 23:28:47 2011 UTC vs.
Revision 1.71 by root, Sat Nov 21 16:53:50 2015 UTC

54only a generic name is used (C<expr>, C<cond>, C<value> and so on), then 54only a generic name is used (C<expr>, C<cond>, C<value> and so on), then
55the corresponding function relies on C to implement the correct types, and 55the corresponding function relies on C to implement the correct types, and
56is usually implemented as a macro. Specifically, a "bool" in this manual 56is usually implemented as a macro. Specifically, a "bool" in this manual
57refers to any kind of boolean value, not a specific type. 57refers to any kind of boolean value, not a specific type.
58 58
59=head2 TYPES / TYPE SUPPORT
60
61ecb.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
67The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
68platform (currently C<4> or C<8>) and can be used in preprocessor
69expressions.
70
71For C<ptrdiff_t> and C<size_t> use C<stddef.h>.
72
73=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
74
75All the following symbols expand to an expression that can be tested in
76preprocessor instructions as well as treated as a boolean (use C<!!> to
77ensure it's either C<0> or C<1> if you need that).
78
79=over 4
80
81=item ECB_C
82
83True if the implementation defines the C<__STDC__> macro to a true value,
84while not claiming to be C++.
85
86=item ECB_C99
87
88True if the implementation claims to be compliant to C99 (ISO/IEC
899899:1999) or any later version, while not claiming to be C++.
90
91Note that later versions (ECB_C11) remove core features again (for
92example, variable length arrays).
93
94=item ECB_C11
95
96True if the implementation claims to be compliant to C11 (ISO/IEC
979899:2011) or any later version, while not claiming to be C++.
98
99=item ECB_CPP
100
101True if the implementation defines the C<__cplusplus__> macro to a true
102value, which is typically true for C++ compilers.
103
104=item ECB_CPP11
105
106True 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
111Expands to a true value (suitable for testing in by the preprocessor)
112if the compiler used is GNU C and the version is the given version, or
113higher.
114
115This macro tries to return false on compilers that claim to be GCC
116compatible but aren't.
117
118=item ECB_EXTERN_C
119
120Expands to C<extern "C"> in C++, and a simple C<extern> in C.
121
122This 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
128These two macros can be used to wrap multiple C<extern "C"> definitions -
129they expand to nothing in C.
130
131They 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
142If this evaluates to a true value (suitable for testing in by the
143preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
144and double/binary64 representations internally I<and> the endianness of
145both types match the endianness of C<uint32_t> and C<uint64_t>.
146
147This means you can just copy the bits of a C<float> (or C<double>) to an
148C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
149without having to think about format or endianness.
150
151This is true for basically all modern platforms, although F<ecb.h> might
152not be able to deduce this correctly everywhere and might err on the safe
153side.
154
155=item ECB_AMD64, ECB_AMD64_X32
156
157These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
158ABI, respectively, and undefined elsewhere.
159
160The designers of the new X32 ABI for some inexplicable reason decided to
161make it look exactly like amd64, even though it's completely incompatible
162to that ABI, breaking about every piece of software that assumed that
163C<__x86_64> stands for, well, the x86-64 ABI, making these macros
164necessary.
165
166=back
167
168=head2 MACRO TRICKERY
169
170=over 4
171
172=item ECB_CONCAT (a, b)
173
174Expands any macros in C<a> and C<b>, then concatenates the result to form
175a single token. This is mainly useful to form identifiers from components,
176e.g.:
177
178 #define S1 str
179 #define S2 cpy
180
181 ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
182
183=item ECB_STRINGIFY (arg)
184
185Expands any macros in C<arg> and returns the stringified version of
186it. This is mainly useful to get the contents of a macro in string form,
187e.g.:
188
189 #define SQL_LIMIT 100
190 sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
191
192=item ECB_STRINGIFY_EXPR (expr)
193
194Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
195is a valid expression. This is useful to catch typos or cases where the
196macro isn't available:
197
198 #include <errno.h>
199
200 ECB_STRINGIFY (EDOM); // "33" (on my system at least)
201 ECB_STRINGIFY_EXPR (EDOM); // "33"
202
203 // now imagine we had a typo:
204
205 ECB_STRINGIFY (EDAM); // "EDAM"
206 ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
207
208=back
209
59=head2 GCC ATTRIBUTES 210=head2 ATTRIBUTES
60 211
61A major part of libecb deals with GCC attributes. These are additional 212A major part of libecb deals with additional attributes that can be
62attributes that you can assign to functions, variables and sometimes even 213assigned to functions, variables and sometimes even types - much like
63types - much like C<const> or C<volatile> in C. 214C<const> or C<volatile> in C. They are implemented using either GCC
64 215attributes or other compiler/language specific features. Attributes
65While GCC allows declarations to show up in many surprising places,
66but not in many expected places, the safest way is to put attribute
67declarations before the whole declaration: 216declarations must be put before the whole declaration:
68 217
69 ecb_const int mysqrt (int a); 218 ecb_const int mysqrt (int a);
70 ecb_unused int i; 219 ecb_unused int i;
71 220
72For variables, it is often nicer to put the attribute after the name, and
73avoid multiple declarations using commas:
74
75 int i ecb_unused;
76
77=over 4 221=over 4
78
79=item ecb_attribute ((attrs...))
80
81A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
82nothing on other compilers, so the effect is that only GCC sees these.
83
84Example: use the C<deprecated> attribute on a function.
85
86 ecb_attribute((__deprecated__)) void
87 do_not_use_me_anymore (void);
88 222
89=item ecb_unused 223=item ecb_unused
90 224
91Marks a function or a variable as "unused", which simply suppresses a 225Marks a function or a variable as "unused", which simply suppresses a
92warning by GCC when it detects it as unused. This is useful when you e.g. 226warning by GCC when it detects it as unused. This is useful when you e.g.
93declare a variable but do not always use it: 227declare a variable but do not always use it:
94 228
95 { 229 {
96 int var ecb_unused; 230 ecb_unused int var;
97 231
98 #ifdef SOMECONDITION 232 #ifdef SOMECONDITION
99 var = ...; 233 var = ...;
100 return var; 234 return var;
101 #else 235 #else
102 return 0; 236 return 0;
103 #endif 237 #endif
104 } 238 }
105 239
240=item ecb_deprecated
241
242Similar to C<ecb_unused>, but marks a function, variable or type as
243deprecated. This makes some compilers warn when the type is used.
244
245=item ecb_deprecated_message (message)
246
247Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
248used instead of a generic depreciation message when the object is being
249used.
250
106=item ecb_inline 251=item ecb_inline
107 252
108This is not actually an attribute, but you use it like one. It expands
109either to C<static inline> or to just C<static>, if inline isn't 253Expands either to C<static inline> or to just C<static>, if inline
110supported. It should be used to declare functions that should be inlined, 254isn't supported. It should be used to declare functions that should be
111for code size or speed reasons. 255inlined, for code size or speed reasons.
112 256
113Example: inline this function, it surely will reduce codesize. 257Example: inline this function, it surely will reduce codesize.
114 258
115 ecb_inline int 259 ecb_inline int
116 negmul (int a, int b) 260 negmul (int a, int b)
118 return - (a * b); 262 return - (a * b);
119 } 263 }
120 264
121=item ecb_noinline 265=item ecb_noinline
122 266
123Prevent a function from being inlined - it might be optimised away, but 267Prevents a function from being inlined - it might be optimised away, but
124not inlined into other functions. This is useful if you know your function 268not inlined into other functions. This is useful if you know your function
125is rarely called and large enough for inlining not to be helpful. 269is rarely called and large enough for inlining not to be helpful.
126 270
127=item ecb_noreturn 271=item ecb_noreturn
128 272
138 } 282 }
139 283
140In this case, the compiler would probably be smart enough to deduce it on 284In this case, the compiler would probably be smart enough to deduce it on
141its own, so this is mainly useful for declarations. 285its own, so this is mainly useful for declarations.
142 286
287=item ecb_restrict
288
289Expands to the C<restrict> keyword or equivalent on compilers that support
290them, and to nothing on others. Must be specified on a pointer type or
291an array index to indicate that the memory doesn't alias with any other
292restricted pointer in the same scope.
293
294Example: multiply a vector, and allow the compiler to parallelise the
295loop, because it knows it doesn't overwrite input values.
296
297 void
298 multiply (ecb_restrict float *src,
299 ecb_restrict float *dst,
300 int len, float factor)
301 {
302 int i;
303
304 for (i = 0; i < len; ++i)
305 dst [i] = src [i] * factor;
306 }
307
143=item ecb_const 308=item ecb_const
144 309
145Declares that the function only depends on the values of its arguments, 310Declares that the function only depends on the values of its arguments,
146much like a mathematical function. It specifically does not read or write 311much like a mathematical function. It specifically does not read or write
147any memory any arguments might point to, global variables, or call any 312any memory any arguments might point to, global variables, or call any
207functions only called in exceptional or rare cases. 372functions only called in exceptional or rare cases.
208 373
209=item ecb_artificial 374=item ecb_artificial
210 375
211Declares the function as "artificial", in this case meaning that this 376Declares the function as "artificial", in this case meaning that this
212function is not really mean to be a function, but more like an accessor 377function is not really meant to be a function, but more like an accessor
213- many methods in C++ classes are mere accessor functions, and having a 378- many methods in C++ classes are mere accessor functions, and having a
214crash reported in such a method, or single-stepping through them, is not 379crash reported in such a method, or single-stepping through them, is not
215usually so helpful, especially when it's inlined to just a few instructions. 380usually so helpful, especially when it's inlined to just a few instructions.
216 381
217Marking them as artificial will instruct the debugger about just this, 382Marking them as artificial will instruct the debugger about just this,
237 402
238=head2 OPTIMISATION HINTS 403=head2 OPTIMISATION HINTS
239 404
240=over 4 405=over 4
241 406
242=item bool ecb_is_constant(expr) 407=item bool ecb_is_constant (expr)
243 408
244Returns true iff the expression can be deduced to be a compile-time 409Returns true iff the expression can be deduced to be a compile-time
245constant, and false otherwise. 410constant, and false otherwise.
246 411
247For example, when you have a C<rndm16> function that returns a 16 bit 412For example, when you have a C<rndm16> function that returns a 16 bit
265 return is_constant (n) && !(n & (n - 1)) 430 return is_constant (n) && !(n & (n - 1))
266 ? rndm16 () & (num - 1) 431 ? rndm16 () & (num - 1)
267 : (n * (uint32_t)rndm16 ()) >> 16; 432 : (n * (uint32_t)rndm16 ()) >> 16;
268 } 433 }
269 434
270=item bool ecb_expect (expr, value) 435=item ecb_expect (expr, value)
271 436
272Evaluates C<expr> and returns it. In addition, it tells the compiler that 437Evaluates C<expr> and returns it. In addition, it tells the compiler that
273the C<expr> evaluates to C<value> a lot, which can be used for static 438the C<expr> evaluates to C<value> a lot, which can be used for static
274branch optimisations. 439branch optimisations.
275 440
322 { 487 {
323 if (ecb_expect_false (current + size > end)) 488 if (ecb_expect_false (current + size > end))
324 real_reserve_method (size); /* presumably noinline */ 489 real_reserve_method (size); /* presumably noinline */
325 } 490 }
326 491
327=item bool ecb_assume (cond) 492=item ecb_assume (cond)
328 493
329Try to tell the compiler that some condition is true, even if it's not 494Tries to tell the compiler that some condition is true, even if it's not
330obvious. 495obvious. This is not a function, but a statement: it cannot be used in
496another expression.
331 497
332This can be used to teach the compiler about invariants or other 498This can be used to teach the compiler about invariants or other
333conditions that might improve code generation, but which are impossible to 499conditions that might improve code generation, but which are impossible to
334deduce form the code itself. 500deduce form the code itself.
335 501
352 518
353Then the compiler I<might> be able to optimise out the second call 519Then the compiler I<might> be able to optimise out the second call
354completely, as it knows that C<< current + 1 > end >> is false and the 520completely, as it knows that C<< current + 1 > end >> is false and the
355call will never be executed. 521call will never be executed.
356 522
357=item bool ecb_unreachable () 523=item ecb_unreachable ()
358 524
359This function does nothing itself, except tell the compiler that it will 525This function does nothing itself, except tell the compiler that it will
360never be executed. Apart from suppressing a warning in some cases, this 526never be executed. Apart from suppressing a warning in some cases, this
361function can be used to implement C<ecb_assume> or similar functions. 527function can be used to implement C<ecb_assume> or similar functionality.
362 528
363=item bool ecb_prefetch (addr, rw, locality) 529=item ecb_prefetch (addr, rw, locality)
364 530
365Tells the compiler to try to prefetch memory at the given C<addr>ess 531Tells the compiler to try to prefetch memory at the given C<addr>ess
366for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of 532for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
367C<0> means that there will only be one access later, C<3> means that 533C<0> means that there will only be one access later, C<3> means that
368the data will likely be accessed very often, and values in between mean 534the data will likely be accessed very often, and values in between mean
369something... in between. The memory pointed to by the address does not 535something... in between. The memory pointed to by the address does not
370need to be accessible (it could be a null pointer for example), but C<rw> 536need to be accessible (it could be a null pointer for example), but C<rw>
371and C<locality> must be compile-time constants. 537and C<locality> must be compile-time constants.
372 538
539This is a statement, not a function: you cannot use it as part of an
540expression.
541
373An obvious way to use this is to prefetch some data far away, in a big 542An obvious way to use this is to prefetch some data far away, in a big
374array you loop over. This prefetches memory some 128 array elements later, 543array you loop over. This prefetches memory some 128 array elements later,
375in the hope that it will be ready when the CPU arrives at that location. 544in the hope that it will be ready when the CPU arrives at that location.
376 545
377 int sum = 0; 546 int sum = 0;
425For example: 594For example:
426 595
427 ecb_ctz32 (3) = 0 596 ecb_ctz32 (3) = 0
428 ecb_ctz32 (6) = 1 597 ecb_ctz32 (6) = 1
429 598
599=item bool ecb_is_pot32 (uint32_t x)
600
601=item bool ecb_is_pot64 (uint32_t x)
602
603Returns true iff C<x> is a power of two or C<x == 0>.
604
605For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
606
430=item int ecb_ld32 (uint32_t x) 607=item int ecb_ld32 (uint32_t x)
431 608
432=item int ecb_ld64 (uint64_t x) 609=item int ecb_ld64 (uint64_t x)
433 610
434Returns the index of the most significant bit set in C<x>, or the number 611Returns the index of the most significant bit set in C<x>, or the number
455For example: 632For example:
456 633
457 ecb_popcount32 (7) = 3 634 ecb_popcount32 (7) = 3
458 ecb_popcount32 (255) = 8 635 ecb_popcount32 (255) = 8
459 636
637=item uint8_t ecb_bitrev8 (uint8_t x)
638
639=item uint16_t ecb_bitrev16 (uint16_t x)
640
641=item uint32_t ecb_bitrev32 (uint32_t x)
642
643Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
644and so on.
645
646Example:
647
648 ecb_bitrev8 (0xa7) = 0xea
649 ecb_bitrev32 (0xffcc4411) = 0x882233ff
650
460=item uint32_t ecb_bswap16 (uint32_t x) 651=item uint32_t ecb_bswap16 (uint32_t x)
461 652
462=item uint32_t ecb_bswap32 (uint32_t x) 653=item uint32_t ecb_bswap32 (uint32_t x)
463 654
464=item uint64_t ecb_bswap64 (uint64_t x) 655=item uint64_t ecb_bswap64 (uint64_t x)
488(C<ecb_rotl>). 679(C<ecb_rotl>).
489 680
490Current GCC versions understand these functions and usually compile them 681Current GCC versions understand these functions and usually compile them
491to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on 682to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
492x86). 683x86).
684
685=back
686
687=head2 FLOATING POINT FIDDLING
688
689=over 4
690
691=item ECB_INFINITY [-UECB_NO_LIBM]
692
693Evaluates to positive infinity if supported by the platform, otherwise to
694a truly huge number.
695
696=item ECB_NAN [-UECB_NO_LIBM]
697
698Evaluates to a quiet NAN if supported by the platform, otherwise to
699C<ECB_INFINITY>.
700
701=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
702
703Same as C<ldexpf>, but always available.
704
705=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
706
707=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
708
709=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
710
711These functions each take an argument in the native C<float> or C<double>
712type and return the IEEE 754 bit representation of it (binary16/half,
713binary32/single or binary64/double precision).
714
715The bit representation is just as IEEE 754 defines it, i.e. the sign bit
716will be the most significant bit, followed by exponent and mantissa.
717
718This function should work even when the native floating point format isn't
719IEEE compliant, of course at a speed and code size penalty, and of course
720also within reasonable limits (it tries to convert NaNs, infinities and
721denormals, but will likely convert negative zero to positive zero).
722
723On all modern platforms (where C<ECB_STDFP> is true), the compiler should
724be able to optimise away this function completely.
725
726These functions can be helpful when serialising floats to the network - you
727can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
728
729Another use for these functions is to manipulate floating point values
730directly.
731
732Silly example: toggle the sign bit of a float.
733
734 /* On gcc-4.7 on amd64, */
735 /* this results in a single add instruction to toggle the bit, and 4 extra */
736 /* instructions to move the float value to an integer register and back. */
737
738 x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
739
740=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
741
742=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
743
744=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
745
746The reverse operation of the previous function - takes the bit
747representation of an IEEE binary16, binary32 or binary64 number (half,
748single or double precision) and converts it to the native C<float> or
749C<double> format.
750
751This function should work even when the native floating point format isn't
752IEEE compliant, of course at a speed and code size penalty, and of course
753also within reasonable limits (it tries to convert normals and denormals,
754and might be lucky for infinities, and with extraordinary luck, also for
755negative zero).
756
757On all modern platforms (where C<ECB_STDFP> is true), the compiler should
758be able to optimise away this function completely.
759
760=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
761
762=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
763
764Convert a IEEE binary32/single precision to binary16/half format, and vice
765versa, handling all details (round-to-even, subnormals, infinity and NaNs)
766correctly.
767
768These are functions are available under C<-DECB_NO_LIBM>, since
769they do not rely on the platform floating point format. The
770C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
771usually what you want.
493 772
494=back 773=back
495 774
496=head2 ARITHMETIC 775=head2 ARITHMETIC
497 776
527 806
528=item x = ecb_div_ru (val, div) 807=item x = ecb_div_ru (val, div)
529 808
530Returns C<val> divided by C<div> rounded down or up, respectively. 809Returns C<val> divided by C<div> rounded down or up, respectively.
531C<val> and C<div> must have integer types and C<div> must be strictly 810C<val> and C<div> must have integer types and C<div> must be strictly
532positive. 811positive. Note that these functions are implemented with macros in C
812and with function templates in C++.
533 813
534=back 814=back
535 815
536=head2 UTILITY 816=head2 UTILITY
537 817
547 for (i = 0; i < ecb_array_length (primes); i++) 827 for (i = 0; i < ecb_array_length (primes); i++)
548 sum += primes [i]; 828 sum += primes [i];
549 829
550=back 830=back
551 831
832=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
552 833
834These symbols need to be defined before including F<ecb.h> the first time.
835
836=over 4
837
838=item ECB_NO_THREADS
839
840If F<ecb.h> is never used from multiple threads, then this symbol can
841be defined, in which case memory fences (and similar constructs) are
842completely removed, leading to more efficient code and fewer dependencies.
843
844Setting this symbol to a true value implies C<ECB_NO_SMP>.
845
846=item ECB_NO_SMP
847
848The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
849multiple threads, but never concurrently (e.g. if the system the program
850runs on has only a single CPU with a single core, no hyperthreading and so
851on), then this symbol can be defined, leading to more efficient code and
852fewer dependencies.
853
854=item ECB_NO_LIBM
855
856When defined to C<1>, do not export any functions that might introduce
857dependencies on the math library (usually called F<-lm>) - these are
858marked with [-UECB_NO_LIBM].
859
860=back
861
862=head1 UNDOCUMENTED FUNCTIONALITY
863
864F<ecb.h> is full of undocumented functionality as well, some of which is
865intended to be internal-use only, some of which we forgot to document, and
866some of which we hide because we are not sure we will keep the interface
867stable.
868
869While you are welcome to rummage around and use whatever you find useful
870(we can't stop you), keep in mind that we will change undocumented
871functionality in incompatible ways without thinking twice, while we are
872considerably more conservative with documented things.
873
874=head1 AUTHORS
875
876C<libecb> is designed and maintained by:
877
878 Emanuele Giaquinta <e.giaquinta@glauco.it>
879 Marc Alexander Lehmann <schmorp@schmorp.de>
880
881

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