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 1.54 by root, Wed Dec 19 23:33:47 2012 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,
84which is typically true for both C and C++ compilers. 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. 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. 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.
108 114
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
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 GCC ATTRIBUTES 232=head2 ATTRIBUTES
169 233
170A major part of libecb deals with GCC attributes. These are additional 234A major part of libecb deals with additional attributes that can be
171attributes that you can assign to functions, variables and sometimes even 235assigned to functions, variables and sometimes even types - much like
172types - much like C<const> or C<volatile> in C. 236C<const> or C<volatile> in C. They are implemented using either GCC
173 237attributes or other compiler/language specific features. Attributes
174While GCC allows declarations to show up in many surprising places,
175but not in many expected places, the safest way is to put attribute
176declarations before the whole declaration: 238declarations must be put before the whole declaration:
177 239
178 ecb_const int mysqrt (int a); 240 ecb_const int mysqrt (int a);
179 ecb_unused int i; 241 ecb_unused int i;
180 242
181For variables, it is often nicer to put the attribute after the name, and
182avoid multiple declarations using commas:
183
184 int i ecb_unused;
185
186=over 4 243=over
187
188=item ecb_attribute ((attrs...))
189
190A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to
191nothing on other compilers, so the effect is that only GCC sees these.
192
193Example: use the C<deprecated> attribute on a function.
194
195 ecb_attribute((__deprecated__)) void
196 do_not_use_me_anymore (void);
197 244
198=item ecb_unused 245=item ecb_unused
199 246
200Marks a function or a variable as "unused", which simply suppresses a 247Marks a function or a variable as "unused", which simply suppresses a
201warning 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
202declare a variable but do not always use it: 249you e.g. declare a variable but do not always use it:
203 250
204 { 251 {
205 int var ecb_unused; 252 ecb_unused int var;
206 253
207 #ifdef SOMECONDITION 254 #ifdef SOMECONDITION
208 var = ...; 255 var = ...;
209 return var; 256 return var;
210 #else 257 #else
211 return 0; 258 return 0;
212 #endif 259 #endif
213 } 260 }
214 261
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
215=item ecb_inline 273=item ecb_inline
216 274
217This 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
218either 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
219supported. It should be used to declare functions that should be inlined, 277functions that should be inlined, for code size or speed reasons.
220for code size or speed reasons.
221 278
222Example: inline this function, it surely will reduce codesize. 279Example: inline this function, it surely will reduce codesize.
223 280
224 ecb_inline int 281 ecb_inline int
225 negmul (int a, int b) 282 negmul (int a, int b)
227 return - (a * b); 284 return - (a * b);
228 } 285 }
229 286
230=item ecb_noinline 287=item ecb_noinline
231 288
232Prevent a function from being inlined - it might be optimised away, but 289Prevents a function from being inlined - it might be optimised away, but
233not 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
234is rarely called and large enough for inlining not to be helpful. 291is rarely called and large enough for inlining not to be helpful.
235 292
236=item ecb_noreturn 293=item ecb_noreturn
237 294
258 315
259Example: multiply a vector, and allow the compiler to parallelise the 316Example: multiply a vector, and allow the compiler to parallelise the
260loop, because it knows it doesn't overwrite input values. 317loop, because it knows it doesn't overwrite input values.
261 318
262 void 319 void
263 multiply (float *ecb_restrict src, 320 multiply (ecb_restrict float *src,
264 float *ecb_restrict dst, 321 ecb_restrict float *dst,
265 int len, float factor) 322 int len, float factor)
266 { 323 {
267 int i; 324 int i;
268 325
269 for (i = 0; i < len; ++i) 326 for (i = 0; i < len; ++i)
365 422
366=back 423=back
367 424
368=head2 OPTIMISATION HINTS 425=head2 OPTIMISATION HINTS
369 426
370=over 4 427=over
371 428
372=item bool ecb_is_constant(expr) 429=item bool ecb_is_constant (expr)
373 430
374Returns 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
375constant, and false otherwise. 432constant, and false otherwise.
376 433
377For 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
395 return is_constant (n) && !(n & (n - 1)) 452 return is_constant (n) && !(n & (n - 1))
396 ? rndm16 () & (num - 1) 453 ? rndm16 () & (num - 1)
397 : (n * (uint32_t)rndm16 ()) >> 16; 454 : (n * (uint32_t)rndm16 ()) >> 16;
398 } 455 }
399 456
400=item bool ecb_expect (expr, value) 457=item ecb_expect (expr, value)
401 458
402Evaluates 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
403the 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
404branch optimisations. 461branch optimisations.
405 462
452 { 509 {
453 if (ecb_expect_false (current + size > end)) 510 if (ecb_expect_false (current + size > end))
454 real_reserve_method (size); /* presumably noinline */ 511 real_reserve_method (size); /* presumably noinline */
455 } 512 }
456 513
457=item bool ecb_assume (cond) 514=item ecb_assume (cond)
458 515
459Try 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
460obvious. 517obvious. This is not a function, but a statement: it cannot be used in
518another expression.
461 519
462This can be used to teach the compiler about invariants or other 520This can be used to teach the compiler about invariants or other
463conditions that might improve code generation, but which are impossible to 521conditions that might improve code generation, but which are impossible to
464deduce form the code itself. 522deduce form the code itself.
465 523
482 540
483Then 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
484completely, 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
485call will never be executed. 543call will never be executed.
486 544
487=item bool ecb_unreachable () 545=item ecb_unreachable ()
488 546
489This function does nothing itself, except tell the compiler that it will 547This function does nothing itself, except tell the compiler that it will
490never be executed. Apart from suppressing a warning in some cases, this 548never be executed. Apart from suppressing a warning in some cases, this
491function can be used to implement C<ecb_assume> or similar functions. 549function can be used to implement C<ecb_assume> or similar functionality.
492 550
493=item bool ecb_prefetch (addr, rw, locality) 551=item ecb_prefetch (addr, rw, locality)
494 552
495Tells 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
496for 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
497C<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
498the 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
499something... in between. The memory pointed to by the address does not 557something... in between. The memory pointed to by the address does not
500need 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>
501and C<locality> must be compile-time constants. 559and C<locality> must be compile-time constants.
502 560
561This is a statement, not a function: you cannot use it as part of an
562expression.
563
503An 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
504array you loop over. This prefetches memory some 128 array elements later, 565array you loop over. This prefetches memory some 128 array elements later,
505in 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.
506 567
507 int sum = 0; 568 int sum = 0;
528 589
529=back 590=back
530 591
531=head2 BIT FIDDLING / BIT WIZARDRY 592=head2 BIT FIDDLING / BIT WIZARDRY
532 593
533=over 4 594=over
534 595
535=item bool ecb_big_endian () 596=item bool ecb_big_endian ()
536 597
537=item bool ecb_little_endian () 598=item bool ecb_little_endian ()
538 599
544 605
545=item int ecb_ctz32 (uint32_t x) 606=item int ecb_ctz32 (uint32_t x)
546 607
547=item int ecb_ctz64 (uint64_t x) 608=item int ecb_ctz64 (uint64_t x)
548 609
610=item int ecb_ctz (T x) [C++]
611
549Returns 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
550equivalently 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
551set), 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.
552 615
553For 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>.
554 617
618The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
619C<uint32_t> and C<uint64_t> types.
620
555For example: 621For example:
556 622
557 ecb_ctz32 (3) = 0 623 ecb_ctz32 (3) = 0
558 ecb_ctz32 (6) = 1 624 ecb_ctz32 (6) = 1
559 625
560=item bool ecb_is_pot32 (uint32_t x) 626=item bool ecb_is_pot32 (uint32_t x)
561 627
562=item bool ecb_is_pot64 (uint32_t x) 628=item bool ecb_is_pot64 (uint32_t x)
563 629
630=item bool ecb_is_pot (T x) [C++]
631
564Return 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>.
565 633
566For 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.
567 638
568=item int ecb_ld32 (uint32_t x) 639=item int ecb_ld32 (uint32_t x)
569 640
570=item int ecb_ld64 (uint64_t x) 641=item int ecb_ld64 (uint64_t x)
642
643=item int ecb_ld64 (T x) [C++]
571 644
572Returns 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
573of 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 <
5742**(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
575to 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
580the 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
581itself requires. 654itself requires.
582 655
583For 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>.
584 657
658The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
659C<uint32_t> and C<uint64_t> types.
660
585=item int ecb_popcount32 (uint32_t x) 661=item int ecb_popcount32 (uint32_t x)
586 662
587=item int ecb_popcount64 (uint64_t x) 663=item int ecb_popcount64 (uint64_t x)
588 664
665=item int ecb_popcount (T x) [C++]
666
589Returns the number of bits set to 1 in C<x>. 667Returns the number of bits set to 1 in C<x>.
590 668
591For 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.
592 673
593For example: 674For example:
594 675
595 ecb_popcount32 (7) = 3 676 ecb_popcount32 (7) = 3
596 ecb_popcount32 (255) = 8 677 ecb_popcount32 (255) = 8
599 680
600=item uint16_t ecb_bitrev16 (uint16_t x) 681=item uint16_t ecb_bitrev16 (uint16_t x)
601 682
602=item uint32_t ecb_bitrev32 (uint32_t x) 683=item uint32_t ecb_bitrev32 (uint32_t x)
603 684
685=item T ecb_bitrev (T x) [C++]
686
604Reverses 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
605and so on. 688and so on.
606 689
690The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
691
607Example: 692Example:
608 693
609 ecb_bitrev8 (0xa7) = 0xea 694 ecb_bitrev8 (0xa7) = 0xea
610 ecb_bitrev32 (0xffcc4411) = 0x882233ff 695 ecb_bitrev32 (0xffcc4411) = 0x882233ff
611 696
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
612=item uint32_t ecb_bswap16 (uint32_t x) 703=item uint32_t ecb_bswap16 (uint32_t x)
613 704
614=item uint32_t ecb_bswap32 (uint32_t x) 705=item uint32_t ecb_bswap32 (uint32_t x)
615 706
616=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)
617 710
618These 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
619C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in 712C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
620C<ecb_bswap32>). 713C<ecb_bswap32>).
621 714
715The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
716C<uint32_t> and C<uint64_t> types.
717
622=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) 718=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
623 719
624=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) 720=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
625 721
626=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 722=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
635 731
636=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) 732=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
637 733
638These 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
639all 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
640(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.
641 738
642Current GCC versions understand these functions and usually compile them 739Current GCC/clang versions understand these functions and usually compile
643to "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>
644x86). 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.
645 1072
646=back 1073=back
647 1074
648=head2 FLOATING POINT FIDDLING 1075=head2 FLOATING POINT FIDDLING
649 1076
650=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]
651 1094
652=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]
653 1096
654=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]
655 1098
656These 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>
657type 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).
658 1102
659The 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
660will be the most significant bit, followed by exponent and mantissa. 1104will be the most significant bit, followed by exponent and mantissa.
661 1105
662This 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
666 1110
667On 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
668be able to optimise away this function completely. 1112be able to optimise away this function completely.
669 1113
670These functions can be helpful when serialising floats to the network - you 1114These functions can be helpful when serialising floats to the network - you
671can 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.
672 1116
673Another use for these functions is to manipulate floating point values 1117Another use for these functions is to manipulate floating point values
674directly. 1118directly.
675 1119
676Silly example: toggle the sign bit of a float. 1120Silly example: toggle the sign bit of a float.
679 /* this results in a single add instruction to toggle the bit, and 4 extra */ 1123 /* this results in a single add instruction to toggle the bit, and 4 extra */
680 /* instructions to move the float value to an integer register and back. */ 1124 /* instructions to move the float value to an integer register and back. */
681 1125
682 x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) 1126 x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U)
683 1127
1128=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
1129
684=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]
685 1131
686=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]
687 1133
688The reverse operation of the previos function - takes the bit representation 1134The reverse operation of the previous function - takes the bit
689of an IEEE binary32 or binary64 number and converts it to the native C<float> 1135representation of an IEEE binary16, binary32 or binary64 number (half,
1136single or double precision) and converts it to the native C<float> or
690or C<double> format. 1137C<double> format.
691 1138
692This 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
693IEEE 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
694also within reasonable limits (it tries to convert normals and denormals, 1141also within reasonable limits (it tries to convert normals and denormals,
695and might be lucky for infinities, and with extraordinary luck, also for 1142and might be lucky for infinities, and with extraordinary luck, also for
696negative zero). 1143negative zero).
697 1144
698On 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
699be able to optimise away this function completely. 1146be able to optimise away this function completely.
700 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
701=back 1161=back
702 1162
703=head2 ARITHMETIC 1163=head2 ARITHMETIC
704 1164
705=over 4 1165=over
706 1166
707=item x = ecb_mod (m, n) 1167=item x = ecb_mod (m, n)
708 1168
709Returns 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
710of the division operation between C<m> and C<n>, using floored 1170of the division operation between C<m> and C<n>, using floored
717C<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
718negatable, 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
719type (this typically excludes the minimum signed integer value, the same 1179type (this typically excludes the minimum signed integer value, the same
720limitation as for C</> and C<%> in C). 1180limitation as for C</> and C<%> in C).
721 1181
722Current GCC versions compile this into an efficient branchless sequence on 1182Current GCC/clang versions compile this into an efficient branchless
723almost all CPUs. 1183sequence on almost all CPUs.
724 1184
725For 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
726array 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
727C<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
728change direction for negative values: 1188change direction for negative values:
741 1201
742=back 1202=back
743 1203
744=head2 UTILITY 1204=head2 UTILITY
745 1205
746=over 4 1206=over
747 1207
748=item element_count = ecb_array_length (name) 1208=item element_count = ecb_array_length (name)
749 1209
750Returns the number of elements in the array C<name>. For example: 1210Returns the number of elements in the array C<name>. For example:
751 1211
759 1219
760=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF 1220=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
761 1221
762These 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.
763 1223
764=over 4 1224=over
765 1225
766=item ECB_NO_THREADS 1226=item ECB_NO_THREADS
767 1227
768If 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
769be defined, in which case memory fences (and similar constructs) are 1229be defined, in which case memory fences (and similar constructs) are
785dependencies on the math library (usually called F<-lm>) - these are 1245dependencies on the math library (usually called F<-lm>) - these are
786marked with [-UECB_NO_LIBM]. 1246marked with [-UECB_NO_LIBM].
787 1247
788=back 1248=back
789 1249
1250=head1 UNDOCUMENTED FUNCTIONALITY
790 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