ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/cvsroot/libecb/ecb.pod
(Generate patch)

Comparing cvsroot/libecb/ecb.pod (file contents):
Revision 1.60 by sf-exg, Wed Feb 11 19:16:12 2015 UTC vs.
Revision 1.94 by root, Sat Jul 31 16:13:30 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>) and can be used in preprocessor 74platform (currently C<4> or C<8>) and can be used in preprocessor
69expressions. 75expressions.
70 76
71For C<ptrdiff_t> and C<size_t> use C<stddef.h>. 77For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>.
72 78
73=head2 LANGUAGE/COMPILER VERSIONS 79=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS
74 80
75All the following symbols expand to an expression that can be tested in 81All the following symbols expand to an expression that can be tested in
76preprocessor instructions as well as treated as a boolean (use C<!!> to 82preprocessor instructions as well as treated as a boolean (use C<!!> to
77ensure it's either C<0> or C<1> if you need that). 83ensure it's either C<0> or C<1> if you need that).
78 84
79=over 4 85=over
80 86
81=item ECB_C 87=item ECB_C
82 88
83True if the implementation defines the C<__STDC__> macro to a true value, 89True if the implementation defines the C<__STDC__> macro to a true value,
84while not claiming to be C++. 90while not claiming to be C++, i..e C, but not C++.
85 91
86=item ECB_C99 92=item ECB_C99
87 93
88True if the implementation claims to be compliant to C99 (ISO/IEC 94True if the implementation claims to be compliant to C99 (ISO/IEC
899899:1999) or any later version, while not claiming to be C++. 959899:1999) or any later version, while not claiming to be C++.
90 96
91Note that later versions (ECB_C11) remove core features again (for 97Note that later versions (ECB_C11) remove core features again (for
92example, variable length arrays). 98example, variable length arrays).
93 99
94=item ECB_C11 100=item ECB_C11, ECB_C17
95 101
96True if the implementation claims to be compliant to C11 (ISO/IEC 102True if the implementation claims to be compliant to C11/C17 (ISO/IEC
979899:2011) or any later version, while not claiming to be C++. 1039899:2011, :20187) or any later version, while not claiming to be C++.
98 104
99=item ECB_CPP 105=item ECB_CPP
100 106
101True if the implementation defines the C<__cplusplus__> macro to a true 107True if the implementation defines the C<__cplusplus__> macro to a true
102value, which is typically true for C++ compilers. 108value, which is typically true for C++ compilers.
103 109
104=item ECB_CPP11 110=item ECB_CPP11, ECB_CPP14, ECB_CPP17
105 111
106True if the implementation claims to be compliant to ISO/IEC 14882:2011 112True if the implementation claims to be compliant to C++11/C++14/C++17
107(C++11) or any later version. 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.
108 123
109=item ECB_GCC_VERSION (major, minor) 124=item ECB_GCC_VERSION (major, minor)
110 125
111Expands to a true value (suitable for testing in by the preprocessor) 126Expands to a true value (suitable for testing by the preprocessor) if the
112if the compiler used is GNU C and the version is the given version, or 127compiler used is GNU C and the version is the given version, or higher.
113higher.
114 128
115This macro tries to return false on compilers that claim to be GCC 129This macro tries to return false on compilers that claim to be GCC
116compatible but aren't. 130compatible but aren't.
117 131
118=item ECB_EXTERN_C 132=item ECB_EXTERN_C
137 151
138 ECB_EXTERN_C_END 152 ECB_EXTERN_C_END
139 153
140=item ECB_STDFP 154=item ECB_STDFP
141 155
142If this evaluates to a true value (suitable for testing in by the 156If this evaluates to a true value (suitable for testing by the
143preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 157preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
144and double/binary64 representations internally I<and> the endianness of 158and double/binary64 representations internally I<and> the endianness of
145both types match the endianness of C<uint32_t> and C<uint64_t>. 159both types match the endianness of C<uint32_t> and C<uint64_t>.
146 160
147This means you can just copy the bits of a C<float> (or C<double>) to an 161This means you can just copy the bits of a C<float> (or C<double>) to an
149without having to think about format or endianness. 163without having to think about format or endianness.
150 164
151This is true for basically all modern platforms, although F<ecb.h> might 165This 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 166not be able to deduce this correctly everywhere and might err on the safe
153side. 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.
154 176
155=item ECB_AMD64, ECB_AMD64_X32 177=item ECB_AMD64, ECB_AMD64_X32
156 178
157These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 179These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32
158ABI, respectively, and undefined elsewhere. 180ABI, respectively, and undefined elsewhere.
163C<__x86_64> stands for, well, the x86-64 ABI, making these macros 185C<__x86_64> stands for, well, the x86-64 ABI, making these macros
164necessary. 186necessary.
165 187
166=back 188=back
167 189
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
168=head2 ATTRIBUTES 232=head2 ATTRIBUTES
169 233
170A major part of libecb deals with additional attributes that can be 234A major part of libecb deals with additional attributes that can be
171assigned to functions, variables and sometimes even types - much like 235assigned to functions, variables and sometimes even types - much like
172C<const> or C<volatile> in C. They are implemented using either GCC 236C<const> or C<volatile> in C. They are implemented using either GCC
174declarations must be put before the whole declaration: 238declarations must be put before the whole declaration:
175 239
176 ecb_const int mysqrt (int a); 240 ecb_const int mysqrt (int a);
177 ecb_unused int i; 241 ecb_unused int i;
178 242
179=over 4 243=over
180 244
181=item ecb_unused 245=item ecb_unused
182 246
183Marks a function or a variable as "unused", which simply suppresses a 247Marks a function or a variable as "unused", which simply suppresses a
184warning 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
185declare a variable but do not always use it: 249you e.g. declare a variable but do not always use it:
186 250
187 { 251 {
188 int var ecb_unused; 252 ecb_unused int var;
189 253
190 #ifdef SOMECONDITION 254 #ifdef SOMECONDITION
191 var = ...; 255 var = ...;
192 return var; 256 return var;
193 #else 257 #else
198=item ecb_deprecated 262=item ecb_deprecated
199 263
200Similar to C<ecb_unused>, but marks a function, variable or type as 264Similar to C<ecb_unused>, but marks a function, variable or type as
201deprecated. This makes some compilers warn when the type is used. 265deprecated. This makes some compilers warn when the type is used.
202 266
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
203=item ecb_inline 273=item ecb_inline
204 274
205Expands either to C<static inline> or to just C<static>, if inline 275Expands either to (a compiler-specific equivalent of) C<static inline> or
206isn't supported. It should be used to declare functions that should be 276to just C<static>, if inline isn't supported. It should be used to declare
207inlined, for code size or speed reasons. 277functions that should be inlined, for code size or speed reasons.
208 278
209Example: inline this function, it surely will reduce codesize. 279Example: inline this function, it surely will reduce codesize.
210 280
211 ecb_inline int 281 ecb_inline int
212 negmul (int a, int b) 282 negmul (int a, int b)
214 return - (a * b); 284 return - (a * b);
215 } 285 }
216 286
217=item ecb_noinline 287=item ecb_noinline
218 288
219Prevent a function from being inlined - it might be optimised away, but 289Prevents a function from being inlined - it might be optimised away, but
220not 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
221is rarely called and large enough for inlining not to be helpful. 291is rarely called and large enough for inlining not to be helpful.
222 292
223=item ecb_noreturn 293=item ecb_noreturn
224 294
245 315
246Example: multiply a vector, and allow the compiler to parallelise the 316Example: multiply a vector, and allow the compiler to parallelise the
247loop, because it knows it doesn't overwrite input values. 317loop, because it knows it doesn't overwrite input values.
248 318
249 void 319 void
250 multiply (float *ecb_restrict src, 320 multiply (ecb_restrict float *src,
251 float *ecb_restrict dst, 321 ecb_restrict float *dst,
252 int len, float factor) 322 int len, float factor)
253 { 323 {
254 int i; 324 int i;
255 325
256 for (i = 0; i < len; ++i) 326 for (i = 0; i < len; ++i)
352 422
353=back 423=back
354 424
355=head2 OPTIMISATION HINTS 425=head2 OPTIMISATION HINTS
356 426
357=over 4 427=over
358 428
359=item bool ecb_is_constant (expr) 429=item bool ecb_is_constant (expr)
360 430
361Returns 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
362constant, and false otherwise. 432constant, and false otherwise.
382 return is_constant (n) && !(n & (n - 1)) 452 return is_constant (n) && !(n & (n - 1))
383 ? rndm16 () & (num - 1) 453 ? rndm16 () & (num - 1)
384 : (n * (uint32_t)rndm16 ()) >> 16; 454 : (n * (uint32_t)rndm16 ()) >> 16;
385 } 455 }
386 456
387=item bool ecb_expect (expr, value) 457=item ecb_expect (expr, value)
388 458
389Evaluates 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
390the 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
391branch optimisations. 461branch optimisations.
392 462
439 { 509 {
440 if (ecb_expect_false (current + size > end)) 510 if (ecb_expect_false (current + size > end))
441 real_reserve_method (size); /* presumably noinline */ 511 real_reserve_method (size); /* presumably noinline */
442 } 512 }
443 513
444=item bool ecb_assume (cond) 514=item ecb_assume (cond)
445 515
446Try 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
447obvious. 517obvious. This is not a function, but a statement: it cannot be used in
518another expression.
448 519
449This can be used to teach the compiler about invariants or other 520This can be used to teach the compiler about invariants or other
450conditions that might improve code generation, but which are impossible to 521conditions that might improve code generation, but which are impossible to
451deduce form the code itself. 522deduce form the code itself.
452 523
469 540
470Then 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
471completely, 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
472call will never be executed. 543call will never be executed.
473 544
474=item bool ecb_unreachable () 545=item ecb_unreachable ()
475 546
476This function does nothing itself, except tell the compiler that it will 547This function does nothing itself, except tell the compiler that it will
477never be executed. Apart from suppressing a warning in some cases, this 548never be executed. Apart from suppressing a warning in some cases, this
478function can be used to implement C<ecb_assume> or similar functions. 549function can be used to implement C<ecb_assume> or similar functionality.
479 550
480=item bool ecb_prefetch (addr, rw, locality) 551=item ecb_prefetch (addr, rw, locality)
481 552
482Tells 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
483for 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
484C<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
485the 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
486something... in between. The memory pointed to by the address does not 557something... in between. The memory pointed to by the address does not
487need 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>
488and C<locality> must be compile-time constants. 559and C<locality> must be compile-time constants.
489 560
561This is a statement, not a function: you cannot use it as part of an
562expression.
563
490An 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
491array you loop over. This prefetches memory some 128 array elements later, 565array you loop over. This prefetches memory some 128 array elements later,
492in 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.
493 567
494 int sum = 0; 568 int sum = 0;
515 589
516=back 590=back
517 591
518=head2 BIT FIDDLING / BIT WIZARDRY 592=head2 BIT FIDDLING / BIT WIZARDRY
519 593
520=over 4 594=over
521 595
522=item bool ecb_big_endian () 596=item bool ecb_big_endian ()
523 597
524=item bool ecb_little_endian () 598=item bool ecb_little_endian ()
525 599
531 605
532=item int ecb_ctz32 (uint32_t x) 606=item int ecb_ctz32 (uint32_t x)
533 607
534=item int ecb_ctz64 (uint64_t x) 608=item int ecb_ctz64 (uint64_t x)
535 609
610=item int ecb_ctz (T x) [C++]
611
536Returns 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
537equivalently 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
538set), 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.
539 615
540For 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>.
541 617
618The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
619C<uint32_t> and C<uint64_t> types.
620
542For example: 621For example:
543 622
544 ecb_ctz32 (3) = 0 623 ecb_ctz32 (3) = 0
545 ecb_ctz32 (6) = 1 624 ecb_ctz32 (6) = 1
546 625
547=item bool ecb_is_pot32 (uint32_t x) 626=item bool ecb_is_pot32 (uint32_t x)
548 627
549=item bool ecb_is_pot64 (uint32_t x) 628=item bool ecb_is_pot64 (uint32_t x)
550 629
630=item bool ecb_is_pot (T x) [C++]
631
551Return 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>.
552 633
553For 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.
554 638
555=item int ecb_ld32 (uint32_t x) 639=item int ecb_ld32 (uint32_t x)
556 640
557=item int ecb_ld64 (uint64_t x) 641=item int ecb_ld64 (uint64_t x)
642
643=item int ecb_ld64 (T x) [C++]
558 644
559Returns 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
560of 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 <
5612**(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
562to 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
567the 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
568itself requires. 654itself requires.
569 655
570For 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>.
571 657
658The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
659C<uint32_t> and C<uint64_t> types.
660
572=item int ecb_popcount32 (uint32_t x) 661=item int ecb_popcount32 (uint32_t x)
573 662
574=item int ecb_popcount64 (uint64_t x) 663=item int ecb_popcount64 (uint64_t x)
575 664
665=item int ecb_popcount (T x) [C++]
666
576Returns the number of bits set to 1 in C<x>. 667Returns the number of bits set to 1 in C<x>.
577 668
578For 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.
579 673
580For example: 674For example:
581 675
582 ecb_popcount32 (7) = 3 676 ecb_popcount32 (7) = 3
583 ecb_popcount32 (255) = 8 677 ecb_popcount32 (255) = 8
586 680
587=item uint16_t ecb_bitrev16 (uint16_t x) 681=item uint16_t ecb_bitrev16 (uint16_t x)
588 682
589=item uint32_t ecb_bitrev32 (uint32_t x) 683=item uint32_t ecb_bitrev32 (uint32_t x)
590 684
685=item T ecb_bitrev (T x) [C++]
686
591Reverses 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
592and so on. 688and so on.
593 689
690The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
691
594Example: 692Example:
595 693
596 ecb_bitrev8 (0xa7) = 0xea 694 ecb_bitrev8 (0xa7) = 0xea
597 ecb_bitrev32 (0xffcc4411) = 0x882233ff 695 ecb_bitrev32 (0xffcc4411) = 0x882233ff
598 696
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
599=item uint32_t ecb_bswap16 (uint32_t x) 703=item uint32_t ecb_bswap16 (uint32_t x)
600 704
601=item uint32_t ecb_bswap32 (uint32_t x) 705=item uint32_t ecb_bswap32 (uint32_t x)
602 706
603=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)
604 710
605These 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
606C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in 712C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
607C<ecb_bswap32>). 713C<ecb_bswap32>).
608 714
715The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
716C<uint32_t> and C<uint64_t> types.
717
609=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) 718=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
610 719
611=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) 720=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
612 721
613=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 722=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
622 731
623=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) 732=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
624 733
625These 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
626all 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
627(C<ecb_rotl>). 736(C<ecb_rotl>). There are no restrictions on the value C<count>, i.e. both
737zero and values equal or larger than the word width work correctly.
628 738
629Current GCC versions understand these functions and usually compile them 739Current GCC/clang versions understand these functions and usually compile
630to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on 740them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
631x86). 741on x86).
742
743=item T ecb_rotl (T x, unsigned int count) [C++]
744
745=item T ecb_rotr (T x, unsigned int count) [C++]
746
747Overloaded C++ rotl/rotr functions.
748
749C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
750
751=back
752
753=head2 HOST ENDIANNESS CONVERSION
754
755=over
756
757=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
758
759=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
760
761=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
762
763=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
764
765=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
766
767=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
768
769Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
770
771The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>,
772where C<be> and C<le> stand for big endian and little endian, respectively.
773
774=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
775
776=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
777
778=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
779
780=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
781
782=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
783
784=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
785
786Like above, but converts I<from> host byte order to the specified
787endianness.
788
789=back
790
791In C++ the following additional template functions are supported:
792
793=over
794
795=item T ecb_be_to_host (T v)
796
797=item T ecb_le_to_host (T v)
798
799=item T ecb_host_to_be (T v)
800
801=item T ecb_host_to_le (T v)
802
803=back
804
805These functions work like their C counterparts, above, but use templates,
806which make them useful in generic code.
807
808C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
809(so unlike their C counterparts, there is a version for C<uint8_t>, which
810again can be useful in generic code).
811
812=head2 UNALIGNED LOAD/STORE
813
814These function load or store unaligned multi-byte values.
815
816=over
817
818=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
819
820=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
821
822=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
823
824These functions load an unaligned, unsigned 16, 32 or 64 bit value from
825memory.
826
827=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
828
829=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
830
831=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
832
833=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
834
835=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
836
837=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
838
839Like above, but additionally convert from big endian (C<be>) or little
840endian (C<le>) byte order to host byte order while doing so.
841
842=item ecb_poke_u16_u (void *ptr, uint16_t v)
843
844=item ecb_poke_u32_u (void *ptr, uint32_t v)
845
846=item ecb_poke_u64_u (void *ptr, uint64_t v)
847
848These functions store an unaligned, unsigned 16, 32 or 64 bit value to
849memory.
850
851=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
852
853=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
854
855=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
856
857=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
858
859=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
860
861=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
862
863Like above, but additionally convert from host byte order to big endian
864(C<be>) or little endian (C<le>) byte order while doing so.
865
866=back
867
868In C++ the following additional template functions are supported:
869
870=over
871
872=item T ecb_peek<T> (const void *ptr)
873
874=item T ecb_peek_be<T> (const void *ptr)
875
876=item T ecb_peek_le<T> (const void *ptr)
877
878=item T ecb_peek_u<T> (const void *ptr)
879
880=item T ecb_peek_be_u<T> (const void *ptr)
881
882=item T ecb_peek_le_u<T> (const void *ptr)
883
884Similarly to their C counterparts, these functions load an unsigned 8, 16,
88532 or 64 bit value from memory, with optional conversion from big/little
886endian.
887
888Since the type cannot be deduced, it has to be specified explicitly, e.g.
889
890 uint_fast16_t v = ecb_peek<uint16_t> (ptr);
891
892C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
893
894Unlike their C counterparts, these functions support 8 bit quantities
895(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
896all of which hopefully makes them more useful in generic code.
897
898=item ecb_poke (void *ptr, T v)
899
900=item ecb_poke_be (void *ptr, T v)
901
902=item ecb_poke_le (void *ptr, T v)
903
904=item ecb_poke_u (void *ptr, T v)
905
906=item ecb_poke_be_u (void *ptr, T v)
907
908=item ecb_poke_le_u (void *ptr, T v)
909
910Again, similarly to their C counterparts, these functions store an
911unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
912big/little endian.
913
914C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
915
916Unlike their C counterparts, these functions support 8 bit quantities
917(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
918all of which hopefully makes them more useful in generic code.
919
920=back
921
922=head2 FAST INTEGER TO STRING
923
924Libecb defines a set of very fast integer to decimal string (or integer
925to ascii, short C<i2a>) functions. These work by converting the integer
926to a fixed point representation and then successively multiplying out
927the topmost digits. Unlike some other, also very fast, libraries, ecb's
928algorithm should be completely branchless per digit, and does not rely on
929the presence of special cpu functions (such as clz).
930
931There is a high level API that takes an C<int32_t>, C<uint32_t>,
932C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
933harder to use but supports slightly more formatting options.
934
935=head3 HIGH LEVEL API
936
937The high level API consists of four functions, one each for C<int32_t>,
938C<uint32_t>, C<int64_t> and C<uint64_t>:
939
940Example:
941
942 char buf[ECB_I2A_MAX_DIGITS + 1];
943 char *end = ecb_i2a_i32 (buf, 17262);
944 *end = 0;
945 // buf now contains "17262"
946
947=over
948
949=item ECB_I2A_I32_DIGITS (=11)
950
951=item char *ecb_i2a_u32 (char *ptr, uint32_t value)
952
953Takes an C<uint32_t> I<value> and formats it as a decimal number starting
954at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
955pointer to just after the generated string, where you would normally put
956the terminating C<0> character. This function outputs the minimum number
957of digits.
958
959=item ECB_I2A_U32_DIGITS (=10)
960
961=item char *ecb_i2a_i32 (char *ptr, int32_t value)
962
963Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
964sign if needed.
965
966=item ECB_I2A_I64_DIGITS (=20)
967
968=item char *ecb_i2a_u64 (char *ptr, uint64_t value)
969
970=item ECB_I2A_U64_DIGITS (=21)
971
972=item char *ecb_i2a_i64 (char *ptr, int64_t value)
973
974Similar to their 32 bit counterparts, these take a 64 bit argument.
975
976=item ECB_I2A_MAX_DIGITS (=21)
977
978Instead of using a type specific length macro, youi can just use
979C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
980
981=back
982
983=head3 LOW-LEVEL API
984
985The functions above use a number of low-level APIs which have some strict
986limitations, but can be used as building blocks (study of C<ecb_i2a_i32>
987and related functions is recommended).
988
989There are three families of functions: functions that convert a number
990to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
991for "leading zeroes"), functions that generate up to N digits, skipping
992leading zeroes (C<_N>), and functions that can generate more digits, but
993the leading digit has limited range (C<_xN>).
994
995None of the functions deal with negative numbers.
996
997Example: convert an IP address in an u32 into dotted-quad:
998
999 uint32_t ip = 0x0a000164; // 10.0.1.100
1000 char ips[3 * 4 + 3 + 1];
1001 char *ptr = ips;
1002 ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
1003 ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
1004 ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
1005 ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
1006 printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
1007
1008=over
1009
1010=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit
1011
1012=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit
1013
1014=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit
1015
1016=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit
1017
1018=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit
1019
1020=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit
1021
1022=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit
1023
1024=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit
1025
1026The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert
1027them to exactly I<N> digits, returning a pointer to the first character
1028after the digits. The I<value> must be in range. The functions marked with
1029I<32 bit> do their calculations internally in 32 bit, the ones marked with
1030I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
1031architectures (the high level API decides on 32 vs. 64 bit versions using
1032C<ECB_64BIT_NATIVE>).
1033
1034=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit
1035
1036=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit
1037
1038=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit
1039
1040=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit
1041
1042=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit
1043
1044=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit
1045
1046=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit
1047
1048=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit
1049
1050Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value>
1051and convert them to at most I<N> digits, suppressing leading zeroes, and
1052returning a pointer to the first character after the digits.
1053
1054=item ECB_I2A_MAX_X5 (=59074)
1055
1056=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit
1057
1058=item ECB_I2A_MAX_X10 (=2932500665)
1059
1060=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit
1061
1062The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >
1063functions, but they can generate one digit more, as long as the number
1064is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
106516 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
1066respectively.
1067
1068For example, the digit part of a 32 bit signed integer just fits into the
1069C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
1070digit number, it can convert all 32 bit signed numbers. Sadly, it's not
1071good enough for 32 bit unsigned numbers.
632 1072
633=back 1073=back
634 1074
635=head2 FLOATING POINT FIDDLING 1075=head2 FLOATING POINT FIDDLING
636 1076
637=over 4 1077=over
1078
1079=item ECB_INFINITY [-UECB_NO_LIBM]
1080
1081Evaluates to positive infinity if supported by the platform, otherwise to
1082a truly huge number.
1083
1084=item ECB_NAN [-UECB_NO_LIBM]
1085
1086Evaluates to a quiet NAN if supported by the platform, otherwise to
1087C<ECB_INFINITY>.
1088
1089=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
1090
1091Same as C<ldexpf>, but always available.
1092
1093=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
638 1094
639=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] 1095=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
640 1096
641=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] 1097=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
642 1098
643These functions each take an argument in the native C<float> or C<double> 1099These functions each take an argument in the native C<float> or C<double>
644type and return the IEEE 754 bit representation of it. 1100type and return the IEEE 754 bit representation of it (binary16/half,
1101binary32/single or binary64/double precision).
645 1102
646The bit representation is just as IEEE 754 defines it, i.e. the sign bit 1103The bit representation is just as IEEE 754 defines it, i.e. the sign bit
647will be the most significant bit, followed by exponent and mantissa. 1104will be the most significant bit, followed by exponent and mantissa.
648 1105
649This function should work even when the native floating point format isn't 1106This function should work even when the native floating point format isn't
653 1110
654On all modern platforms (where C<ECB_STDFP> is true), the compiler should 1111On all modern platforms (where C<ECB_STDFP> is true), the compiler should
655be able to optimise away this function completely. 1112be able to optimise away this function completely.
656 1113
657These functions can be helpful when serialising floats to the network - you 1114These functions can be helpful when serialising floats to the network - you
658can serialise the return value like a normal uint32_t/uint64_t. 1115can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
659 1116
660Another use for these functions is to manipulate floating point values 1117Another use for these functions is to manipulate floating point values
661directly. 1118directly.
662 1119
663Silly example: toggle the sign bit of a float. 1120Silly example: toggle the sign bit of a float.
670 1127
671=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] 1128=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
672 1129
673=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] 1130=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
674 1131
675=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] 1132=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
676 1133
677The reverse operation of the previous function - takes the bit 1134The reverse operation of the previous function - takes the bit
678representation of an IEEE binary16, binary32 or binary64 number and 1135representation of an IEEE binary16, binary32 or binary64 number (half,
679converts it to the native C<float> or C<double> format. 1136single or double precision) and converts it to the native C<float> or
1137C<double> format.
680 1138
681This function should work even when the native floating point format isn't 1139This function should work even when the native floating point format isn't
682IEEE compliant, of course at a speed and code size penalty, and of course 1140IEEE compliant, of course at a speed and code size penalty, and of course
683also within reasonable limits (it tries to convert normals and denormals, 1141also within reasonable limits (it tries to convert normals and denormals,
684and might be lucky for infinities, and with extraordinary luck, also for 1142and might be lucky for infinities, and with extraordinary luck, also for
685negative zero). 1143negative zero).
686 1144
687On all modern platforms (where C<ECB_STDFP> is true), the compiler should 1145On all modern platforms (where C<ECB_STDFP> is true), the compiler should
688be able to optimise away this function completely. 1146be able to optimise away this function completely.
689 1147
1148=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
1149
1150=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
1151
1152Convert a IEEE binary32/single precision to binary16/half format, and vice
1153versa, handling all details (round-to-nearest-even, subnormals, infinity
1154and NaNs) correctly.
1155
1156These are functions are available under C<-DECB_NO_LIBM>, since
1157they do not rely on the platform floating point format. The
1158C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
1159usually what you want.
1160
690=back 1161=back
691 1162
692=head2 ARITHMETIC 1163=head2 ARITHMETIC
693 1164
694=over 4 1165=over
695 1166
696=item x = ecb_mod (m, n) 1167=item x = ecb_mod (m, n)
697 1168
698Returns C<m> modulo C<n>, which is the same as the positive remainder 1169Returns C<m> modulo C<n>, which is the same as the positive remainder
699of the division operation between C<m> and C<n>, using floored 1170of the division operation between C<m> and C<n>, using floored
706C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 1177C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
707negatable, that is, both C<m> and C<-m> must be representable in its 1178negatable, that is, both C<m> and C<-m> must be representable in its
708type (this typically excludes the minimum signed integer value, the same 1179type (this typically excludes the minimum signed integer value, the same
709limitation as for C</> and C<%> in C). 1180limitation as for C</> and C<%> in C).
710 1181
711Current GCC versions compile this into an efficient branchless sequence on 1182Current GCC/clang versions compile this into an efficient branchless
712almost all CPUs. 1183sequence on almost all CPUs.
713 1184
714For example, when you want to rotate forward through the members of an 1185For example, when you want to rotate forward through the members of an
715array for increasing C<m> (which might be negative), then you should use 1186array for increasing C<m> (which might be negative), then you should use
716C<ecb_mod>, as the C<%> operator might give either negative results, or 1187C<ecb_mod>, as the C<%> operator might give either negative results, or
717change direction for negative values: 1188change direction for negative values:
730 1201
731=back 1202=back
732 1203
733=head2 UTILITY 1204=head2 UTILITY
734 1205
735=over 4 1206=over
736 1207
737=item element_count = ecb_array_length (name) 1208=item element_count = ecb_array_length (name)
738 1209
739Returns the number of elements in the array C<name>. For example: 1210Returns the number of elements in the array C<name>. For example:
740 1211
748 1219
749=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF 1220=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
750 1221
751These symbols need to be defined before including F<ecb.h> the first time. 1222These symbols need to be defined before including F<ecb.h> the first time.
752 1223
753=over 4 1224=over
754 1225
755=item ECB_NO_THREADS 1226=item ECB_NO_THREADS
756 1227
757If F<ecb.h> is never used from multiple threads, then this symbol can 1228If F<ecb.h> is never used from multiple threads, then this symbol can
758be defined, in which case memory fences (and similar constructs) are 1229be defined, in which case memory fences (and similar constructs) are
774dependencies on the math library (usually called F<-lm>) - these are 1245dependencies on the math library (usually called F<-lm>) - these are
775marked with [-UECB_NO_LIBM]. 1246marked with [-UECB_NO_LIBM].
776 1247
777=back 1248=back
778 1249
1250=head1 UNDOCUMENTED FUNCTIONALITY
779 1251
1252F<ecb.h> is full of undocumented functionality as well, some of which is
1253intended to be internal-use only, some of which we forgot to document, and
1254some of which we hide because we are not sure we will keep the interface
1255stable.
1256
1257While you are welcome to rummage around and use whatever you find useful
1258(we can't stop you), keep in mind that we will change undocumented
1259functionality in incompatible ways without thinking twice, while we are
1260considerably more conservative with documented things.
1261
1262=head1 AUTHORS
1263
1264C<libecb> is designed and maintained by:
1265
1266 Emanuele Giaquinta <e.giaquinta@glauco.it>
1267 Marc Alexander Lehmann <schmorp@schmorp.de>
1268
1269

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines