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Revision 1.41 by root, Mon May 28 08:40:25 2012 UTC vs.
Revision 1.92 by sf-exg, Tue Jun 22 05:28:44 2021 UTC

10 10
11Its homepage can be found here: 11Its homepage can be found here:
12 12
13 http://software.schmorp.de/pkg/libecb 13 http://software.schmorp.de/pkg/libecb
14 14
15It mainly provides a number of wrappers around GCC built-ins, together 15It mainly provides a number of wrappers around many compiler built-ins,
16with replacement functions for other compilers. In addition to this, 16together with replacement functions for other compilers. In addition
17it provides a number of other lowlevel C utilities, such as endianness 17to this, it provides a number of other lowlevel C utilities, such as
18detection, byte swapping or bit rotations. 18endianness detection, byte swapping or bit rotations.
19 19
20Or in other words, things that should be built into any standard C system, 20Or in other words, things that should be built into any standard C
21but aren't, implemented as efficient as possible with GCC, and still 21system, but aren't, implemented as efficient as possible with GCC (clang,
22correct with other compilers. 22msvc...), and still correct with other compilers.
23 23
24More might come. 24More might come.
25 25
26=head2 ABOUT THE HEADER 26=head2 ABOUT THE HEADER
27 27
58 58
59=head2 TYPES / TYPE SUPPORT 59=head2 TYPES / TYPE SUPPORT
60 60
61ecb.h makes sure that the following types are defined (in the expected way): 61ecb.h makes sure that the following types are defined (in the expected way):
62 62
63 int8_t uint8_t int16_t uint16_t 63 int8_t uint8_
64 int32_t uint32_t int64_t uint64_t 64 int16_t uint16_t
65 int32_t uint32_
66 int64_t uint64_t
67 int_fast8_t uint_fast8_t
68 int_fast16_t uint_fast16_t
69 int_fast32_t uint_fast32_t
70 int_fast64_t uint_fast64_t
65 intptr_t uintptr_t 71 intptr_t uintptr_t
66 72
67The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this 73The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
68platform (currently C<4> or C<8>). 74platform (currently C<4> or C<8>) and can be used in preprocessor
75expressions.
69 76
77For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>.
78
79=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
80
81All the following symbols expand to an expression that can be tested in
82preprocessor instructions as well as treated as a boolean (use C<!!> to
83ensure it's either C<0> or C<1> if you need that).
84
85=over
86
87=item ECB_C
88
89True if the implementation defines the C<__STDC__> macro to a true value,
90while not claiming to be C++, i..e C, but not C++.
91
92=item ECB_C99
93
94True if the implementation claims to be compliant to C99 (ISO/IEC
959899:1999) or any later version, while not claiming to be C++.
96
97Note that later versions (ECB_C11) remove core features again (for
98example, variable length arrays).
99
100=item ECB_C11, ECB_C17
101
102True if the implementation claims to be compliant to C11/C17 (ISO/IEC
1039899:2011, :20187) or any later version, while not claiming to be C++.
104
105=item ECB_CPP
106
107True if the implementation defines the C<__cplusplus__> macro to a true
108value, which is typically true for C++ compilers.
109
110=item ECB_CPP11, ECB_CPP14, ECB_CPP17
111
112True if the implementation claims to be compliant to C++11/C++14/C++17
113(ISO/IEC 14882:2011, :2014, :2017) or any later version.
114
115Note that many C++20 features will likely have their own feature test
116macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>).
117
118=item ECB_OPTIMIZE_SIZE
119
120Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
121can also be defined before including F<ecb.h>, in which case it will be
122unchanged.
123
124=item ECB_GCC_VERSION (major, minor)
125
126Expands to a true value (suitable for testing by the preprocessor) if the
127compiler used is GNU C and the version is the given version, or higher.
128
129This macro tries to return false on compilers that claim to be GCC
130compatible but aren't.
131
132=item ECB_EXTERN_C
133
134Expands to C<extern "C"> in C++, and a simple C<extern> in C.
135
136This can be used to declare a single external C function:
137
138 ECB_EXTERN_C int printf (const char *format, ...);
139
140=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END
141
142These two macros can be used to wrap multiple C<extern "C"> definitions -
143they expand to nothing in C.
144
145They are most useful in header files:
146
147 ECB_EXTERN_C_BEG
148
149 int mycfun1 (int x);
150 int mycfun2 (int x);
151
152 ECB_EXTERN_C_END
153
154=item ECB_STDFP
155
156If this evaluates to a true value (suitable for testing by the
157preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
158and double/binary64 representations internally I<and> the endianness of
159both types match the endianness of C<uint32_t> and C<uint64_t>.
160
161This means you can just copy the bits of a C<float> (or C<double>) to an
162C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation
163without having to think about format or endianness.
164
165This is true for basically all modern platforms, although F<ecb.h> might
166not be able to deduce this correctly everywhere and might err on the safe
167side.
168
169=item ECB_64BIT_NATIVE
170
171Evaluates to a true value (suitable for both preprocessor and C code
172testing) if 64 bit integer types on this architecture are evaluated
173"natively", that is, with similar speeds as 32 bit integers. While 64 bit
174integer support is very common (and in fact required by libecb), 32 bit
175cpus have to emulate operations on them, so you might want to avoid them.
176
177=item ECB_AMD64, ECB_AMD64_X32
178
179These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
180ABI, respectively, and undefined elsewhere.
181
182The designers of the new X32 ABI for some inexplicable reason decided to
183make it look exactly like amd64, even though it's completely incompatible
184to that ABI, breaking about every piece of software that assumed that
185C<__x86_64> stands for, well, the x86-64 ABI, making these macros
186necessary.
187
188=back
189
190=head2 MACRO TRICKERY
191
192=over
193
194=item ECB_CONCAT (a, b)
195
196Expands any macros in C<a> and C<b>, then concatenates the result to form
197a single token. This is mainly useful to form identifiers from components,
198e.g.:
199
200 #define S1 str
201 #define S2 cpy
202
203 ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src);
204
205=item ECB_STRINGIFY (arg)
206
207Expands any macros in C<arg> and returns the stringified version of
208it. This is mainly useful to get the contents of a macro in string form,
209e.g.:
210
211 #define SQL_LIMIT 100
212 sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT));
213
214=item ECB_STRINGIFY_EXPR (expr)
215
216Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it
217is a valid expression. This is useful to catch typos or cases where the
218macro isn't available:
219
220 #include <errno.h>
221
222 ECB_STRINGIFY (EDOM); // "33" (on my system at least)
223 ECB_STRINGIFY_EXPR (EDOM); // "33"
224
225 // now imagine we had a typo:
226
227 ECB_STRINGIFY (EDAM); // "EDAM"
228 ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined
229
230=back
231
70=head2 GCC ATTRIBUTES 232=head2 ATTRIBUTES
71 233
72A major part of libecb deals with GCC attributes. These are additional 234A major part of libecb deals with additional attributes that can be
73attributes that you can assign to functions, variables and sometimes even 235assigned to functions, variables and sometimes even types - much like
74types - much like C<const> or C<volatile> in C. 236C<const> or C<volatile> in C. They are implemented using either GCC
75 237attributes or other compiler/language specific features. Attributes
76While GCC allows declarations to show up in many surprising places,
77but not in many expected places, the safest way is to put attribute
78declarations before the whole declaration: 238declarations must be put before the whole declaration:
79 239
80 ecb_const int mysqrt (int a); 240 ecb_const int mysqrt (int a);
81 ecb_unused int i; 241 ecb_unused int i;
82 242
83For variables, it is often nicer to put the attribute after the name, and
84avoid multiple declarations using commas:
85
86 int i ecb_unused;
87
88=over 4 243=over
89
90=item ecb_attribute ((attrs...))
91
92A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
93nothing on other compilers, so the effect is that only GCC sees these.
94
95Example: use the C<deprecated> attribute on a function.
96
97 ecb_attribute((__deprecated__)) void
98 do_not_use_me_anymore (void);
99 244
100=item ecb_unused 245=item ecb_unused
101 246
102Marks a function or a variable as "unused", which simply suppresses a 247Marks a function or a variable as "unused", which simply suppresses a
103warning by GCC when it detects it as unused. This is useful when you e.g. 248warning by the compiler when it detects it as unused. This is useful when
104declare a variable but do not always use it: 249you e.g. declare a variable but do not always use it:
105 250
106 { 251 {
107 int var ecb_unused; 252 ecb_unused int var;
108 253
109 #ifdef SOMECONDITION 254 #ifdef SOMECONDITION
110 var = ...; 255 var = ...;
111 return var; 256 return var;
112 #else 257 #else
113 return 0; 258 return 0;
114 #endif 259 #endif
115 } 260 }
116 261
262=item ecb_deprecated
263
264Similar to C<ecb_unused>, but marks a function, variable or type as
265deprecated. This makes some compilers warn when the type is used.
266
267=item ecb_deprecated_message (message)
268
269Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
270used instead of a generic depreciation message when the object is being
271used.
272
117=item ecb_inline 273=item ecb_inline
118 274
119This is not actually an attribute, but you use it like one. It expands 275Expands either to (a compiler-specific equivalent of) C<static inline> or
120either to C<static inline> or to just C<static>, if inline isn't 276to just C<static>, if inline isn't supported. It should be used to declare
121supported. It should be used to declare functions that should be inlined, 277functions that should be inlined, for code size or speed reasons.
122for code size or speed reasons.
123 278
124Example: inline this function, it surely will reduce codesize. 279Example: inline this function, it surely will reduce codesize.
125 280
126 ecb_inline int 281 ecb_inline int
127 negmul (int a, int b) 282 negmul (int a, int b)
129 return - (a * b); 284 return - (a * b);
130 } 285 }
131 286
132=item ecb_noinline 287=item ecb_noinline
133 288
134Prevent a function from being inlined - it might be optimised away, but 289Prevents a function from being inlined - it might be optimised away, but
135not inlined into other functions. This is useful if you know your function 290not inlined into other functions. This is useful if you know your function
136is rarely called and large enough for inlining not to be helpful. 291is rarely called and large enough for inlining not to be helpful.
137 292
138=item ecb_noreturn 293=item ecb_noreturn
139 294
149 } 304 }
150 305
151In this case, the compiler would probably be smart enough to deduce it on 306In this case, the compiler would probably be smart enough to deduce it on
152its own, so this is mainly useful for declarations. 307its own, so this is mainly useful for declarations.
153 308
309=item ecb_restrict
310
311Expands to the C<restrict> keyword or equivalent on compilers that support
312them, and to nothing on others. Must be specified on a pointer type or
313an array index to indicate that the memory doesn't alias with any other
314restricted pointer in the same scope.
315
316Example: multiply a vector, and allow the compiler to parallelise the
317loop, because it knows it doesn't overwrite input values.
318
319 void
320 multiply (ecb_restrict float *src,
321 ecb_restrict float *dst,
322 int len, float factor)
323 {
324 int i;
325
326 for (i = 0; i < len; ++i)
327 dst [i] = src [i] * factor;
328 }
329
154=item ecb_const 330=item ecb_const
155 331
156Declares that the function only depends on the values of its arguments, 332Declares that the function only depends on the values of its arguments,
157much like a mathematical function. It specifically does not read or write 333much like a mathematical function. It specifically does not read or write
158any memory any arguments might point to, global variables, or call any 334any memory any arguments might point to, global variables, or call any
218functions only called in exceptional or rare cases. 394functions only called in exceptional or rare cases.
219 395
220=item ecb_artificial 396=item ecb_artificial
221 397
222Declares the function as "artificial", in this case meaning that this 398Declares the function as "artificial", in this case meaning that this
223function is not really mean to be a function, but more like an accessor 399function is not really meant to be a function, but more like an accessor
224- many methods in C++ classes are mere accessor functions, and having a 400- many methods in C++ classes are mere accessor functions, and having a
225crash reported in such a method, or single-stepping through them, is not 401crash reported in such a method, or single-stepping through them, is not
226usually so helpful, especially when it's inlined to just a few instructions. 402usually so helpful, especially when it's inlined to just a few instructions.
227 403
228Marking them as artificial will instruct the debugger about just this, 404Marking them as artificial will instruct the debugger about just this,
246 422
247=back 423=back
248 424
249=head2 OPTIMISATION HINTS 425=head2 OPTIMISATION HINTS
250 426
251=over 4 427=over
252 428
253=item bool ecb_is_constant(expr) 429=item bool ecb_is_constant (expr)
254 430
255Returns true iff the expression can be deduced to be a compile-time 431Returns true iff the expression can be deduced to be a compile-time
256constant, and false otherwise. 432constant, and false otherwise.
257 433
258For example, when you have a C<rndm16> function that returns a 16 bit 434For example, when you have a C<rndm16> function that returns a 16 bit
276 return is_constant (n) && !(n & (n - 1)) 452 return is_constant (n) && !(n & (n - 1))
277 ? rndm16 () & (num - 1) 453 ? rndm16 () & (num - 1)
278 : (n * (uint32_t)rndm16 ()) >> 16; 454 : (n * (uint32_t)rndm16 ()) >> 16;
279 } 455 }
280 456
281=item bool ecb_expect (expr, value) 457=item ecb_expect (expr, value)
282 458
283Evaluates C<expr> and returns it. In addition, it tells the compiler that 459Evaluates C<expr> and returns it. In addition, it tells the compiler that
284the C<expr> evaluates to C<value> a lot, which can be used for static 460the C<expr> evaluates to C<value> a lot, which can be used for static
285branch optimisations. 461branch optimisations.
286 462
333 { 509 {
334 if (ecb_expect_false (current + size > end)) 510 if (ecb_expect_false (current + size > end))
335 real_reserve_method (size); /* presumably noinline */ 511 real_reserve_method (size); /* presumably noinline */
336 } 512 }
337 513
338=item bool ecb_assume (cond) 514=item ecb_assume (cond)
339 515
340Try to tell the compiler that some condition is true, even if it's not 516Tries to tell the compiler that some condition is true, even if it's not
341obvious. 517obvious. This is not a function, but a statement: it cannot be used in
518another expression.
342 519
343This can be used to teach the compiler about invariants or other 520This can be used to teach the compiler about invariants or other
344conditions that might improve code generation, but which are impossible to 521conditions that might improve code generation, but which are impossible to
345deduce form the code itself. 522deduce form the code itself.
346 523
363 540
364Then the compiler I<might> be able to optimise out the second call 541Then the compiler I<might> be able to optimise out the second call
365completely, as it knows that C<< current + 1 > end >> is false and the 542completely, as it knows that C<< current + 1 > end >> is false and the
366call will never be executed. 543call will never be executed.
367 544
368=item bool ecb_unreachable () 545=item ecb_unreachable ()
369 546
370This function does nothing itself, except tell the compiler that it will 547This function does nothing itself, except tell the compiler that it will
371never be executed. Apart from suppressing a warning in some cases, this 548never be executed. Apart from suppressing a warning in some cases, this
372function can be used to implement C<ecb_assume> or similar functions. 549function can be used to implement C<ecb_assume> or similar functionality.
373 550
374=item bool ecb_prefetch (addr, rw, locality) 551=item ecb_prefetch (addr, rw, locality)
375 552
376Tells the compiler to try to prefetch memory at the given C<addr>ess 553Tells the compiler to try to prefetch memory at the given C<addr>ess
377for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of 554for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of
378C<0> means that there will only be one access later, C<3> means that 555C<0> means that there will only be one access later, C<3> means that
379the data will likely be accessed very often, and values in between mean 556the data will likely be accessed very often, and values in between mean
380something... in between. The memory pointed to by the address does not 557something... in between. The memory pointed to by the address does not
381need to be accessible (it could be a null pointer for example), but C<rw> 558need to be accessible (it could be a null pointer for example), but C<rw>
382and C<locality> must be compile-time constants. 559and C<locality> must be compile-time constants.
383 560
561This is a statement, not a function: you cannot use it as part of an
562expression.
563
384An obvious way to use this is to prefetch some data far away, in a big 564An obvious way to use this is to prefetch some data far away, in a big
385array you loop over. This prefetches memory some 128 array elements later, 565array you loop over. This prefetches memory some 128 array elements later,
386in the hope that it will be ready when the CPU arrives at that location. 566in the hope that it will be ready when the CPU arrives at that location.
387 567
388 int sum = 0; 568 int sum = 0;
409 589
410=back 590=back
411 591
412=head2 BIT FIDDLING / BIT WIZARDRY 592=head2 BIT FIDDLING / BIT WIZARDRY
413 593
414=over 4 594=over
415 595
416=item bool ecb_big_endian () 596=item bool ecb_big_endian ()
417 597
418=item bool ecb_little_endian () 598=item bool ecb_little_endian ()
419 599
425 605
426=item int ecb_ctz32 (uint32_t x) 606=item int ecb_ctz32 (uint32_t x)
427 607
428=item int ecb_ctz64 (uint64_t x) 608=item int ecb_ctz64 (uint64_t x)
429 609
610=item int ecb_ctz (T x) [C++]
611
430Returns the index of the least significant bit set in C<x> (or 612Returns the index of the least significant bit set in C<x> (or
431equivalently the number of bits set to 0 before the least significant bit 613equivalently the number of bits set to 0 before the least significant bit
432set), starting from 0. If C<x> is 0 the result is undefined. 614set), starting from 0. If C<x> is 0 the result is undefined.
433 615
434For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. 616For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
435 617
618The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
619C<uint32_t> and C<uint64_t> types.
620
436For example: 621For example:
437 622
438 ecb_ctz32 (3) = 0 623 ecb_ctz32 (3) = 0
439 ecb_ctz32 (6) = 1 624 ecb_ctz32 (6) = 1
440 625
441=item bool ecb_is_pot32 (uint32_t x) 626=item bool ecb_is_pot32 (uint32_t x)
442 627
443=item bool ecb_is_pot64 (uint32_t x) 628=item bool ecb_is_pot64 (uint32_t x)
444 629
630=item bool ecb_is_pot (T x) [C++]
631
445Return true iff C<x> is a power of two or C<x == 0>. 632Returns true iff C<x> is a power of two or C<x == 0>.
446 633
447For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. 634For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
635
636The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
637C<uint32_t> and C<uint64_t> types.
448 638
449=item int ecb_ld32 (uint32_t x) 639=item int ecb_ld32 (uint32_t x)
450 640
451=item int ecb_ld64 (uint64_t x) 641=item int ecb_ld64 (uint64_t x)
642
643=item int ecb_ld64 (T x) [C++]
452 644
453Returns the index of the most significant bit set in C<x>, or the number 645Returns the index of the most significant bit set in C<x>, or the number
454of digits the number requires in binary (so that C<< 2**ld <= x < 646of digits the number requires in binary (so that C<< 2**ld <= x <
4552**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is 6472**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
456to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for 648to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
461the given data type), while C<ecb_ld> returns how many bits the number 653the given data type), while C<ecb_ld> returns how many bits the number
462itself requires. 654itself requires.
463 655
464For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. 656For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
465 657
658The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
659C<uint32_t> and C<uint64_t> types.
660
466=item int ecb_popcount32 (uint32_t x) 661=item int ecb_popcount32 (uint32_t x)
467 662
468=item int ecb_popcount64 (uint64_t x) 663=item int ecb_popcount64 (uint64_t x)
469 664
665=item int ecb_popcount (T x) [C++]
666
470Returns the number of bits set to 1 in C<x>. 667Returns the number of bits set to 1 in C<x>.
471 668
472For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. 669For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
670
671The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
672C<uint32_t> and C<uint64_t> types.
473 673
474For example: 674For example:
475 675
476 ecb_popcount32 (7) = 3 676 ecb_popcount32 (7) = 3
477 ecb_popcount32 (255) = 8 677 ecb_popcount32 (255) = 8
480 680
481=item uint16_t ecb_bitrev16 (uint16_t x) 681=item uint16_t ecb_bitrev16 (uint16_t x)
482 682
483=item uint32_t ecb_bitrev32 (uint32_t x) 683=item uint32_t ecb_bitrev32 (uint32_t x)
484 684
685=item T ecb_bitrev (T x) [C++]
686
485Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 687Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
486and so on. 688and so on.
487 689
690The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
691
488Example: 692Example:
489 693
490 ecb_bitrev8 (0xa7) = 0xea 694 ecb_bitrev8 (0xa7) = 0xea
491 ecb_bitrev32 (0xffcc4411) = 0x882233ff 695 ecb_bitrev32 (0xffcc4411) = 0x882233ff
492 696
697=item T ecb_bitrev (T x) [C++]
698
699Overloaded C++ bitrev function.
700
701C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
702
493=item uint32_t ecb_bswap16 (uint32_t x) 703=item uint32_t ecb_bswap16 (uint32_t x)
494 704
495=item uint32_t ecb_bswap32 (uint32_t x) 705=item uint32_t ecb_bswap32 (uint32_t x)
496 706
497=item uint64_t ecb_bswap64 (uint64_t x) 707=item uint64_t ecb_bswap64 (uint64_t x)
708
709=item T ecb_bswap (T x)
498 710
499These functions return the value of the 16-bit (32-bit, 64-bit) value 711These functions return the value of the 16-bit (32-bit, 64-bit) value
500C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in 712C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
501C<ecb_bswap32>). 713C<ecb_bswap32>).
502 714
715The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
716C<uint32_t> and C<uint64_t> types.
717
503=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) 718=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
504 719
505=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) 720=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
506 721
507=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 722=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
518 733
519These two families of functions return the value of C<x> after rotating 734These two families of functions return the value of C<x> after rotating
520all the bits by C<count> positions to the right (C<ecb_rotr>) or left 735all the bits by C<count> positions to the right (C<ecb_rotr>) or left
521(C<ecb_rotl>). 736(C<ecb_rotl>).
522 737
523Current GCC versions understand these functions and usually compile them 738Current GCC/clang versions understand these functions and usually compile
524to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on 739them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
525x86). 740on x86).
741
742=item T ecb_rotl (T x, unsigned int count) [C++]
743
744=item T ecb_rotr (T x, unsigned int count) [C++]
745
746Overloaded C++ rotl/rotr functions.
747
748C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
749
750=back
751
752=head2 HOST ENDIANNESS CONVERSION
753
754=over
755
756=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
757
758=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
759
760=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
761
762=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
763
764=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
765
766=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
767
768Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
769
770The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>,
771where C<be> and C<le> stand for big endian and little endian, respectively.
772
773=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
774
775=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
776
777=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
778
779=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
780
781=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
782
783=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
784
785Like above, but converts I<from> host byte order to the specified
786endianness.
787
788=back
789
790In C++ the following additional template functions are supported:
791
792=over
793
794=item T ecb_be_to_host (T v)
795
796=item T ecb_le_to_host (T v)
797
798=item T ecb_host_to_be (T v)
799
800=item T ecb_host_to_le (T v)
801
802=back
803
804These functions work like their C counterparts, above, but use templates,
805which make them useful in generic code.
806
807C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
808(so unlike their C counterparts, there is a version for C<uint8_t>, which
809again can be useful in generic code).
810
811=head2 UNALIGNED LOAD/STORE
812
813These function load or store unaligned multi-byte values.
814
815=over
816
817=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
818
819=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
820
821=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
822
823These functions load an unaligned, unsigned 16, 32 or 64 bit value from
824memory.
825
826=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
827
828=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
829
830=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
831
832=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
833
834=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
835
836=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
837
838Like above, but additionally convert from big endian (C<be>) or little
839endian (C<le>) byte order to host byte order while doing so.
840
841=item ecb_poke_u16_u (void *ptr, uint16_t v)
842
843=item ecb_poke_u32_u (void *ptr, uint32_t v)
844
845=item ecb_poke_u64_u (void *ptr, uint64_t v)
846
847These functions store an unaligned, unsigned 16, 32 or 64 bit value to
848memory.
849
850=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
851
852=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
853
854=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
855
856=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
857
858=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
859
860=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
861
862Like above, but additionally convert from host byte order to big endian
863(C<be>) or little endian (C<le>) byte order while doing so.
864
865=back
866
867In C++ the following additional template functions are supported:
868
869=over
870
871=item T ecb_peek<T> (const void *ptr)
872
873=item T ecb_peek_be<T> (const void *ptr)
874
875=item T ecb_peek_le<T> (const void *ptr)
876
877=item T ecb_peek_u<T> (const void *ptr)
878
879=item T ecb_peek_be_u<T> (const void *ptr)
880
881=item T ecb_peek_le_u<T> (const void *ptr)
882
883Similarly to their C counterparts, these functions load an unsigned 8, 16,
88432 or 64 bit value from memory, with optional conversion from big/little
885endian.
886
887Since the type cannot be deduced, it has to be specified explicitly, e.g.
888
889 uint_fast16_t v = ecb_peek<uint16_t> (ptr);
890
891C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
892
893Unlike their C counterparts, these functions support 8 bit quantities
894(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
895all of which hopefully makes them more useful in generic code.
896
897=item ecb_poke (void *ptr, T v)
898
899=item ecb_poke_be (void *ptr, T v)
900
901=item ecb_poke_le (void *ptr, T v)
902
903=item ecb_poke_u (void *ptr, T v)
904
905=item ecb_poke_be_u (void *ptr, T v)
906
907=item ecb_poke_le_u (void *ptr, T v)
908
909Again, similarly to their C counterparts, these functions store an
910unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
911big/little endian.
912
913C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
914
915Unlike their C counterparts, these functions support 8 bit quantities
916(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
917all of which hopefully makes them more useful in generic code.
918
919=back
920
921=head2 FAST INTEGER TO STRING
922
923Libecb defines a set of very fast integer to decimal string (or integer
924to ascii, short C<i2a>) functions. These work by converting the integer
925to a fixed point representation and then successively multiplying out
926the topmost digits. Unlike some other, also very fast, libraries, ecb's
927algorithm should be completely branchless per digit, and does not rely on
928the presence of special cpu functions (such as clz).
929
930There is a high level API that takes an C<int32_t>, C<uint32_t>,
931C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
932harder to use but supports slightly more formatting options.
933
934=head3 HIGH LEVEL API
935
936The high level API consists of four functions, one each for C<int32_t>,
937C<uint32_t>, C<int64_t> and C<uint64_t>:
938
939Example:
940
941 char buf[ECB_I2A_MAX_DIGITS + 1];
942 char *end = ecb_i2a_i32 (buf, 17262);
943 *end = 0;
944 // buf now contains "17262"
945
946=over
947
948=item ECB_I2A_I32_DIGITS (=11)
949
950=item char *ecb_i2a_u32 (char *ptr, uint32_t value)
951
952Takes an C<uint32_t> I<value> and formats it as a decimal number starting
953at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
954pointer to just after the generated string, where you would normally put
955the terminating C<0> character. This function outputs the minimum number
956of digits.
957
958=item ECB_I2A_U32_DIGITS (=10)
959
960=item char *ecb_i2a_i32 (char *ptr, int32_t value)
961
962Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
963sign if needed.
964
965=item ECB_I2A_I64_DIGITS (=20)
966
967=item char *ecb_i2a_u64 (char *ptr, uint64_t value)
968
969=item ECB_I2A_U64_DIGITS (=21)
970
971=item char *ecb_i2a_i64 (char *ptr, int64_t value)
972
973Similar to their 32 bit counterparts, these take a 64 bit argument.
974
975=item ECB_I2A_MAX_DIGITS (=21)
976
977Instead of using a type specific length macro, youi can just use
978C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
979
980=back
981
982=head3 LOW-LEVEL API
983
984The functions above use a number of low-level APIs which have some strict
985limitations, but can be used as building blocks (study of C<ecb_i2a_i32>
986and related functions is recommended).
987
988There are three families of functions: functions that convert a number
989to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
990for "leading zeroes"), functions that generate up to N digits, skipping
991leading zeroes (C<_N>), and functions that can generate more digits, but
992the leading digit has limited range (C<_xN>).
993
994None of the functions deal with negative numbers.
995
996Example: convert an IP address in an u32 into dotted-quad:
997
998 uint32_t ip = 0x0a000164; // 10.0.1.100
999 char ips[3 * 4 + 3 + 1];
1000 char *ptr = ips;
1001 ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
1002 ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
1003 ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
1004 ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
1005 printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
1006
1007=over
1008
1009=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit
1010
1011=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit
1012
1013=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit
1014
1015=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit
1016
1017=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit
1018
1019=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit
1020
1021=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit
1022
1023=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit
1024
1025The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert
1026them to exactly I<N> digits, returning a pointer to the first character
1027after the digits. The I<value> must be in range. The functions marked with
1028I<32 bit> do their calculations internally in 32 bit, the ones marked with
1029I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
1030architectures (the high level API decides on 32 vs. 64 bit versions using
1031C<ECB_64BIT_NATIVE>).
1032
1033=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit
1034
1035=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit
1036
1037=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit
1038
1039=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit
1040
1041=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit
1042
1043=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit
1044
1045=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit
1046
1047=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit
1048
1049Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value>
1050and convert them to at most I<N> digits, suppressing leading zeroes, and
1051returning a pointer to the first character after the digits.
1052
1053=item ECB_I2A_MAX_X5 (=59074)
1054
1055=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit
1056
1057=item ECB_I2A_MAX_X10 (=2932500665)
1058
1059=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit
1060
1061The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >
1062functions, but they can generate one digit more, as long as the number
1063is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
106416 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
1065respectively.
1066
1067For example, the digit part of a 32 bit signed integer just fits into the
1068C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
1069digit number, it can convert all 32 bit signed numbers. Sadly, it's not
1070good enough for 32 bit unsigned numbers.
1071
1072=back
1073
1074=head2 FLOATING POINT FIDDLING
1075
1076=over
1077
1078=item ECB_INFINITY [-UECB_NO_LIBM]
1079
1080Evaluates to positive infinity if supported by the platform, otherwise to
1081a truly huge number.
1082
1083=item ECB_NAN [-UECB_NO_LIBM]
1084
1085Evaluates to a quiet NAN if supported by the platform, otherwise to
1086C<ECB_INFINITY>.
1087
1088=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
1089
1090Same as C<ldexpf>, but always available.
1091
1092=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
1093
1094=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
1095
1096=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
1097
1098These functions each take an argument in the native C<float> or C<double>
1099type and return the IEEE 754 bit representation of it (binary16/half,
1100binary32/single or binary64/double precision).
1101
1102The bit representation is just as IEEE 754 defines it, i.e. the sign bit
1103will be the most significant bit, followed by exponent and mantissa.
1104
1105This function should work even when the native floating point format isn't
1106IEEE compliant, of course at a speed and code size penalty, and of course
1107also within reasonable limits (it tries to convert NaNs, infinities and
1108denormals, but will likely convert negative zero to positive zero).
1109
1110On all modern platforms (where C<ECB_STDFP> is true), the compiler should
1111be able to optimise away this function completely.
1112
1113These functions can be helpful when serialising floats to the network - you
1114can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
1115
1116Another use for these functions is to manipulate floating point values
1117directly.
1118
1119Silly example: toggle the sign bit of a float.
1120
1121 /* On gcc-4.7 on amd64, */
1122 /* this results in a single add instruction to toggle the bit, and 4 extra */
1123 /* instructions to move the float value to an integer register and back. */
1124
1125 x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
1126
1127=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
1128
1129=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
1130
1131=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
1132
1133The reverse operation of the previous function - takes the bit
1134representation of an IEEE binary16, binary32 or binary64 number (half,
1135single or double precision) and converts it to the native C<float> or
1136C<double> format.
1137
1138This function should work even when the native floating point format isn't
1139IEEE compliant, of course at a speed and code size penalty, and of course
1140also within reasonable limits (it tries to convert normals and denormals,
1141and might be lucky for infinities, and with extraordinary luck, also for
1142negative zero).
1143
1144On all modern platforms (where C<ECB_STDFP> is true), the compiler should
1145be able to optimise away this function completely.
1146
1147=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
1148
1149=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
1150
1151Convert a IEEE binary32/single precision to binary16/half format, and vice
1152versa, handling all details (round-to-nearest-even, subnormals, infinity
1153and NaNs) correctly.
1154
1155These are functions are available under C<-DECB_NO_LIBM>, since
1156they do not rely on the platform floating point format. The
1157C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
1158usually what you want.
526 1159
527=back 1160=back
528 1161
529=head2 ARITHMETIC 1162=head2 ARITHMETIC
530 1163
531=over 4 1164=over
532 1165
533=item x = ecb_mod (m, n) 1166=item x = ecb_mod (m, n)
534 1167
535Returns C<m> modulo C<n>, which is the same as the positive remainder 1168Returns C<m> modulo C<n>, which is the same as the positive remainder
536of the division operation between C<m> and C<n>, using floored 1169of the division operation between C<m> and C<n>, using floored
543C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 1176C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
544negatable, that is, both C<m> and C<-m> must be representable in its 1177negatable, that is, both C<m> and C<-m> must be representable in its
545type (this typically excludes the minimum signed integer value, the same 1178type (this typically excludes the minimum signed integer value, the same
546limitation as for C</> and C<%> in C). 1179limitation as for C</> and C<%> in C).
547 1180
548Current GCC versions compile this into an efficient branchless sequence on 1181Current GCC/clang versions compile this into an efficient branchless
549almost all CPUs. 1182sequence on almost all CPUs.
550 1183
551For example, when you want to rotate forward through the members of an 1184For example, when you want to rotate forward through the members of an
552array for increasing C<m> (which might be negative), then you should use 1185array for increasing C<m> (which might be negative), then you should use
553C<ecb_mod>, as the C<%> operator might give either negative results, or 1186C<ecb_mod>, as the C<%> operator might give either negative results, or
554change direction for negative values: 1187change direction for negative values:
567 1200
568=back 1201=back
569 1202
570=head2 UTILITY 1203=head2 UTILITY
571 1204
572=over 4 1205=over
573 1206
574=item element_count = ecb_array_length (name) 1207=item element_count = ecb_array_length (name)
575 1208
576Returns the number of elements in the array C<name>. For example: 1209Returns the number of elements in the array C<name>. For example:
577 1210
581 for (i = 0; i < ecb_array_length (primes); i++) 1214 for (i = 0; i < ecb_array_length (primes); i++)
582 sum += primes [i]; 1215 sum += primes [i];
583 1216
584=back 1217=back
585 1218
1219=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
586 1220
1221These symbols need to be defined before including F<ecb.h> the first time.
1222
1223=over
1224
1225=item ECB_NO_THREADS
1226
1227If F<ecb.h> is never used from multiple threads, then this symbol can
1228be defined, in which case memory fences (and similar constructs) are
1229completely removed, leading to more efficient code and fewer dependencies.
1230
1231Setting this symbol to a true value implies C<ECB_NO_SMP>.
1232
1233=item ECB_NO_SMP
1234
1235The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from
1236multiple threads, but never concurrently (e.g. if the system the program
1237runs on has only a single CPU with a single core, no hyperthreading and so
1238on), then this symbol can be defined, leading to more efficient code and
1239fewer dependencies.
1240
1241=item ECB_NO_LIBM
1242
1243When defined to C<1>, do not export any functions that might introduce
1244dependencies on the math library (usually called F<-lm>) - these are
1245marked with [-UECB_NO_LIBM].
1246
1247=back
1248
1249=head1 UNDOCUMENTED FUNCTIONALITY
1250
1251F<ecb.h> is full of undocumented functionality as well, some of which is
1252intended to be internal-use only, some of which we forgot to document, and
1253some of which we hide because we are not sure we will keep the interface
1254stable.
1255
1256While you are welcome to rummage around and use whatever you find useful
1257(we can't stop you), keep in mind that we will change undocumented
1258functionality in incompatible ways without thinking twice, while we are
1259considerably more conservative with documented things.
1260
1261=head1 AUTHORS
1262
1263C<libecb> is designed and maintained by:
1264
1265 Emanuele Giaquinta <e.giaquinta@glauco.it>
1266 Marc Alexander Lehmann <schmorp@schmorp.de>
1267
1268

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