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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/ENVIRONMENT/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.
165 187
166=back 188=back
167 189
168=head2 MACRO TRICKERY 190=head2 MACRO TRICKERY
169 191
170=over 4 192=over
171 193
172=item ECB_CONCAT (a, b) 194=item ECB_CONCAT (a, b)
173 195
174Expands any macros in C<a> and C<b>, then concatenates the result to form 196Expands any macros in C<a> and C<b>, then concatenates the result to form
175a single token. This is mainly useful to form identifiers from components, 197a single token. This is mainly useful to form identifiers from components,
216declarations must be put before the whole declaration: 238declarations must be put before the whole declaration:
217 239
218 ecb_const int mysqrt (int a); 240 ecb_const int mysqrt (int a);
219 ecb_unused int i; 241 ecb_unused int i;
220 242
221=over 4 243=over
222 244
223=item ecb_unused 245=item ecb_unused
224 246
225Marks a function or a variable as "unused", which simply suppresses a 247Marks a function or a variable as "unused", which simply suppresses a
226warning 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
227declare a variable but do not always use it: 249you e.g. declare a variable but do not always use it:
228 250
229 { 251 {
230 ecb_unused int var; 252 ecb_unused int var;
231 253
232 #ifdef SOMECONDITION 254 #ifdef SOMECONDITION
242Similar 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
243deprecated. This makes some compilers warn when the type is used. 265deprecated. This makes some compilers warn when the type is used.
244 266
245=item ecb_deprecated_message (message) 267=item ecb_deprecated_message (message)
246 268
247Same as C<ecb_deprecated>, but if possible, supply a diagnostic that is 269Same as C<ecb_deprecated>, but if possible, the specified diagnostic is
248used instead of a generic depreciation message when the object is being 270used instead of a generic depreciation message when the object is being
249used. 271used.
250 272
251=item ecb_inline 273=item ecb_inline
252 274
253Expands either to C<static inline> or to just C<static>, if inline 275Expands either to (a compiler-specific equivalent of) C<static inline> or
254isn'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
255inlined, for code size or speed reasons. 277functions that should be inlined, for code size or speed reasons.
256 278
257Example: inline this function, it surely will reduce codesize. 279Example: inline this function, it surely will reduce codesize.
258 280
259 ecb_inline int 281 ecb_inline int
260 negmul (int a, int b) 282 negmul (int a, int b)
262 return - (a * b); 284 return - (a * b);
263 } 285 }
264 286
265=item ecb_noinline 287=item ecb_noinline
266 288
267Prevent a function from being inlined - it might be optimised away, but 289Prevents a function from being inlined - it might be optimised away, but
268not 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
269is rarely called and large enough for inlining not to be helpful. 291is rarely called and large enough for inlining not to be helpful.
270 292
271=item ecb_noreturn 293=item ecb_noreturn
272 294
400 422
401=back 423=back
402 424
403=head2 OPTIMISATION HINTS 425=head2 OPTIMISATION HINTS
404 426
405=over 4 427=over
406 428
407=item bool ecb_is_constant (expr) 429=item bool ecb_is_constant (expr)
408 430
409Returns 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
410constant, and false otherwise. 432constant, and false otherwise.
489 real_reserve_method (size); /* presumably noinline */ 511 real_reserve_method (size); /* presumably noinline */
490 } 512 }
491 513
492=item ecb_assume (cond) 514=item ecb_assume (cond)
493 515
494Try 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
495obvious. 517obvious. This is not a function, but a statement: it cannot be used in
518another expression.
496 519
497This can be used to teach the compiler about invariants or other 520This can be used to teach the compiler about invariants or other
498conditions that might improve code generation, but which are impossible to 521conditions that might improve code generation, but which are impossible to
499deduce form the code itself. 522deduce form the code itself.
500 523
521 544
522=item ecb_unreachable () 545=item ecb_unreachable ()
523 546
524This function does nothing itself, except tell the compiler that it will 547This function does nothing itself, except tell the compiler that it will
525never be executed. Apart from suppressing a warning in some cases, this 548never be executed. Apart from suppressing a warning in some cases, this
526function can be used to implement C<ecb_assume> or similar functions. 549function can be used to implement C<ecb_assume> or similar functionality.
527 550
528=item ecb_prefetch (addr, rw, locality) 551=item ecb_prefetch (addr, rw, locality)
529 552
530Tells 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
531for 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
533the 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
534something... in between. The memory pointed to by the address does not 557something... in between. The memory pointed to by the address does not
535need 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>
536and C<locality> must be compile-time constants. 559and C<locality> must be compile-time constants.
537 560
561This is a statement, not a function: you cannot use it as part of an
562expression.
563
538An 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
539array you loop over. This prefetches memory some 128 array elements later, 565array you loop over. This prefetches memory some 128 array elements later,
540in 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.
541 567
542 int sum = 0; 568 int sum = 0;
563 589
564=back 590=back
565 591
566=head2 BIT FIDDLING / BIT WIZARDRY 592=head2 BIT FIDDLING / BIT WIZARDRY
567 593
568=over 4 594=over
569 595
570=item bool ecb_big_endian () 596=item bool ecb_big_endian ()
571 597
572=item bool ecb_little_endian () 598=item bool ecb_little_endian ()
573 599
579 605
580=item int ecb_ctz32 (uint32_t x) 606=item int ecb_ctz32 (uint32_t x)
581 607
582=item int ecb_ctz64 (uint64_t x) 608=item int ecb_ctz64 (uint64_t x)
583 609
610=item int ecb_ctz (T x) [C++]
611
584Returns 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
585equivalently 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
586set), 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.
587 615
588For 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>.
589 617
618The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
619C<uint32_t> and C<uint64_t> types.
620
590For example: 621For example:
591 622
592 ecb_ctz32 (3) = 0 623 ecb_ctz32 (3) = 0
593 ecb_ctz32 (6) = 1 624 ecb_ctz32 (6) = 1
594 625
595=item bool ecb_is_pot32 (uint32_t x) 626=item bool ecb_is_pot32 (uint32_t x)
596 627
597=item bool ecb_is_pot64 (uint32_t x) 628=item bool ecb_is_pot64 (uint32_t x)
598 629
630=item bool ecb_is_pot (T x) [C++]
631
599Return 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>.
600 633
601For 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.
602 638
603=item int ecb_ld32 (uint32_t x) 639=item int ecb_ld32 (uint32_t x)
604 640
605=item int ecb_ld64 (uint64_t x) 641=item int ecb_ld64 (uint64_t x)
642
643=item int ecb_ld64 (T x) [C++]
606 644
607Returns 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
608of 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 <
6092**(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
610to 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
615the 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
616itself requires. 654itself requires.
617 655
618For 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>.
619 657
658The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
659C<uint32_t> and C<uint64_t> types.
660
620=item int ecb_popcount32 (uint32_t x) 661=item int ecb_popcount32 (uint32_t x)
621 662
622=item int ecb_popcount64 (uint64_t x) 663=item int ecb_popcount64 (uint64_t x)
623 664
665=item int ecb_popcount (T x) [C++]
666
624Returns the number of bits set to 1 in C<x>. 667Returns the number of bits set to 1 in C<x>.
625 668
626For 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.
627 673
628For example: 674For example:
629 675
630 ecb_popcount32 (7) = 3 676 ecb_popcount32 (7) = 3
631 ecb_popcount32 (255) = 8 677 ecb_popcount32 (255) = 8
634 680
635=item uint16_t ecb_bitrev16 (uint16_t x) 681=item uint16_t ecb_bitrev16 (uint16_t x)
636 682
637=item uint32_t ecb_bitrev32 (uint32_t x) 683=item uint32_t ecb_bitrev32 (uint32_t x)
638 684
685=item T ecb_bitrev (T x) [C++]
686
639Reverses 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
640and so on. 688and so on.
641 689
690The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
691
642Example: 692Example:
643 693
644 ecb_bitrev8 (0xa7) = 0xea 694 ecb_bitrev8 (0xa7) = 0xea
645 ecb_bitrev32 (0xffcc4411) = 0x882233ff 695 ecb_bitrev32 (0xffcc4411) = 0x882233ff
646 696
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
647=item uint32_t ecb_bswap16 (uint32_t x) 703=item uint32_t ecb_bswap16 (uint32_t x)
648 704
649=item uint32_t ecb_bswap32 (uint32_t x) 705=item uint32_t ecb_bswap32 (uint32_t x)
650 706
651=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)
652 710
653These 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
654C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in 712C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
655C<ecb_bswap32>). 713C<ecb_bswap32>).
656 714
715The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
716C<uint32_t> and C<uint64_t> types.
717
657=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) 718=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
658 719
659=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) 720=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
660 721
661=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 722=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
670 731
671=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) 732=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
672 733
673These 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
674all 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
675(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. Also,
738notwithstanding C<count> being unsigned, negative numbers work and shift
739to the opposite direction.
676 740
677Current GCC versions understand these functions and usually compile them 741Current GCC/clang versions understand these functions and usually compile
678to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on 742them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
679x86). 743on x86).
744
745=item T ecb_rotl (T x, unsigned int count) [C++]
746
747=item T ecb_rotr (T x, unsigned int count) [C++]
748
749Overloaded C++ rotl/rotr functions.
750
751C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
752
753=back
754
755=head2 BIT MIXING, HASHING
756
757Sometimes you have an integer and want to distribute its bits well, for
758example, to use it as a hash in a hashtable. A common example is pointer
759values, which often only have a limited range (e.g. low and high bits are
760often zero).
761
762The following functions try to mix the bits to get a good bias-free
763distribution. They were mainly made for pointers, but the underlying
764integer functions are exposed as well.
765
766As an added benefit, the functions are reversible, so if you find it
767convenient to store only the hash value, you can recover the original
768pointer from the hash ("unmix"), as long as your pinters are 32 or 64 bit
769(if this isn't the case on your platform, drop us a note and we will add
770functions for other bit widths).
771
772The unmix functions are very slightly slower than the mix functions, so
773it is equally very slightly preferable to store the original values wehen
774convenient.
775
776The underlying algorithm if subject to change, so currently these
777functions are not suitable for persistent hash tables, as their result
778value can change between diferent versions of libecb.
779
780=over
781
782=item uintptr_t ecb_ptrmix (void *ptr)
783
784Mixes the bits of a pointer so the result is suitable for hash table
785lookups. In other words, this hashes the pointer value.
786
787=item uintptr_t ecb_ptrmix (T *ptr) [C++]
788
789Overload the C<ecb_ptrmix> function to work for any pointer in C++.
790
791=item void *ecb_ptrunmix (uintptr_t v)
792
793Unmix the hash value into the original pointer. This only works as long
794as the hash value is not truncated, i.e. you used C<uintptr_t> (or
795equivalent) throughout to store it.
796
797=item T *ecb_ptrunmix<T> (uintptr_t v) [C++]
798
799The somewhat less useful template version of C<ecb_ptrunmix> for
800C++. Example:
801
802 sometype *myptr;
803 uintptr_t hash = ecb_ptrmix (myptr);
804 sometype *orig = ecb_ptrunmix<sometype> (hash);
805
806=item uint32_t ecb_mix32 (uint32_t v)
807
808=item uint64_t ecb_mix64 (uint64_t v)
809
810Sometimes you don't have a pointer but an integer whose values are very
811badly distributed. In this case you cna sue these integer versions of the
812mixing function. No C++ template is provided currently.
813
814=item uint32_t ecb_unmix32 (uint32_t v)
815
816=item uint64_t ecb_unmix64 (uint64_t v)
817
818The reverse of the C<ecb_mix> functions - they take a mixed/hashed value
819and recover the original value.
820
821=back
822
823=head2 HOST ENDIANNESS CONVERSION
824
825=over
826
827=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v)
828
829=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v)
830
831=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v)
832
833=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v)
834
835=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v)
836
837=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
838
839Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
840
841The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>,
842where C<be> and C<le> stand for big endian and little endian, respectively.
843
844=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
845
846=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
847
848=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v)
849
850=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v)
851
852=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v)
853
854=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v)
855
856Like above, but converts I<from> host byte order to the specified
857endianness.
858
859=back
860
861In C++ the following additional template functions are supported:
862
863=over
864
865=item T ecb_be_to_host (T v)
866
867=item T ecb_le_to_host (T v)
868
869=item T ecb_host_to_be (T v)
870
871=item T ecb_host_to_le (T v)
872
873=back
874
875These functions work like their C counterparts, above, but use templates,
876which make them useful in generic code.
877
878C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
879(so unlike their C counterparts, there is a version for C<uint8_t>, which
880again can be useful in generic code).
881
882=head2 UNALIGNED LOAD/STORE
883
884These function load or store unaligned multi-byte values.
885
886=over
887
888=item uint_fast16_t ecb_peek_u16_u (const void *ptr)
889
890=item uint_fast32_t ecb_peek_u32_u (const void *ptr)
891
892=item uint_fast64_t ecb_peek_u64_u (const void *ptr)
893
894These functions load an unaligned, unsigned 16, 32 or 64 bit value from
895memory.
896
897=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr)
898
899=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr)
900
901=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr)
902
903=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr)
904
905=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr)
906
907=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr)
908
909Like above, but additionally convert from big endian (C<be>) or little
910endian (C<le>) byte order to host byte order while doing so.
911
912=item ecb_poke_u16_u (void *ptr, uint16_t v)
913
914=item ecb_poke_u32_u (void *ptr, uint32_t v)
915
916=item ecb_poke_u64_u (void *ptr, uint64_t v)
917
918These functions store an unaligned, unsigned 16, 32 or 64 bit value to
919memory.
920
921=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v)
922
923=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v)
924
925=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v)
926
927=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v)
928
929=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v)
930
931=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v)
932
933Like above, but additionally convert from host byte order to big endian
934(C<be>) or little endian (C<le>) byte order while doing so.
935
936=back
937
938In C++ the following additional template functions are supported:
939
940=over
941
942=item T ecb_peek<T> (const void *ptr)
943
944=item T ecb_peek_be<T> (const void *ptr)
945
946=item T ecb_peek_le<T> (const void *ptr)
947
948=item T ecb_peek_u<T> (const void *ptr)
949
950=item T ecb_peek_be_u<T> (const void *ptr)
951
952=item T ecb_peek_le_u<T> (const void *ptr)
953
954Similarly to their C counterparts, these functions load an unsigned 8, 16,
95532 or 64 bit value from memory, with optional conversion from big/little
956endian.
957
958Since the type cannot be deduced, it has to be specified explicitly, e.g.
959
960 uint_fast16_t v = ecb_peek<uint16_t> (ptr);
961
962C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
963
964Unlike their C counterparts, these functions support 8 bit quantities
965(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
966all of which hopefully makes them more useful in generic code.
967
968=item ecb_poke (void *ptr, T v)
969
970=item ecb_poke_be (void *ptr, T v)
971
972=item ecb_poke_le (void *ptr, T v)
973
974=item ecb_poke_u (void *ptr, T v)
975
976=item ecb_poke_be_u (void *ptr, T v)
977
978=item ecb_poke_le_u (void *ptr, T v)
979
980Again, similarly to their C counterparts, these functions store an
981unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to
982big/little endian.
983
984C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
985
986Unlike their C counterparts, these functions support 8 bit quantities
987(C<uint8_t>) and also have an aligned version (without the C<_u> prefix),
988all of which hopefully makes them more useful in generic code.
989
990=back
991
992=head2 FAST INTEGER TO STRING
993
994Libecb defines a set of very fast integer to decimal string (or integer
995to ascii, short C<i2a>) functions. These work by converting the integer
996to a fixed point representation and then successively multiplying out
997the topmost digits. Unlike some other, also very fast, libraries, ecb's
998algorithm should be completely branchless per digit, and does not rely on
999the presence of special cpu functions (such as clz).
1000
1001There is a high level API that takes an C<int32_t>, C<uint32_t>,
1002C<int64_t> or C<uint64_t> as argument, and a low-level API, which is
1003harder to use but supports slightly more formatting options.
1004
1005=head3 HIGH LEVEL API
1006
1007The high level API consists of four functions, one each for C<int32_t>,
1008C<uint32_t>, C<int64_t> and C<uint64_t>:
1009
1010Example:
1011
1012 char buf[ECB_I2A_MAX_DIGITS + 1];
1013 char *end = ecb_i2a_i32 (buf, 17262);
1014 *end = 0;
1015 // buf now contains "17262"
1016
1017=over
1018
1019=item ECB_I2A_I32_DIGITS (=11)
1020
1021=item char *ecb_i2a_u32 (char *ptr, uint32_t value)
1022
1023Takes an C<uint32_t> I<value> and formats it as a decimal number starting
1024at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a
1025pointer to just after the generated string, where you would normally put
1026the terminating C<0> character. This function outputs the minimum number
1027of digits.
1028
1029=item ECB_I2A_U32_DIGITS (=10)
1030
1031=item char *ecb_i2a_i32 (char *ptr, int32_t value)
1032
1033Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus
1034sign if needed.
1035
1036=item ECB_I2A_I64_DIGITS (=20)
1037
1038=item char *ecb_i2a_u64 (char *ptr, uint64_t value)
1039
1040=item ECB_I2A_U64_DIGITS (=21)
1041
1042=item char *ecb_i2a_i64 (char *ptr, int64_t value)
1043
1044Similar to their 32 bit counterparts, these take a 64 bit argument.
1045
1046=item ECB_I2A_MAX_DIGITS (=21)
1047
1048Instead of using a type specific length macro, you can just use
1049C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function.
1050
1051=back
1052
1053=head3 LOW-LEVEL API
1054
1055The functions above use a number of low-level APIs which have some strict
1056limitations, but can be used as building blocks (studying C<ecb_i2a_i32>
1057and related functions is recommended).
1058
1059There are three families of functions: functions that convert a number
1060to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0>
1061for "leading zeroes"), functions that generate up to N digits, skipping
1062leading zeroes (C<_N>), and functions that can generate more digits, but
1063the leading digit has limited range (C<_xN>).
1064
1065None of the functions deal with negative numbers.
1066
1067Example: convert an IP address in an u32 into dotted-quad:
1068
1069 uint32_t ip = 0x0a000164; // 10.0.1.100
1070 char ips[3 * 4 + 3 + 1];
1071 char *ptr = ips;
1072 ptr = ecb_i2a_3 (ptr, ip >> 24 ); *ptr++ = '.';
1073 ptr = ecb_i2a_3 (ptr, (ip >> 16) & 0xff); *ptr++ = '.';
1074 ptr = ecb_i2a_3 (ptr, (ip >> 8) & 0xff); *ptr++ = '.';
1075 ptr = ecb_i2a_3 (ptr, ip & 0xff); *ptr++ = 0;
1076 printf ("ip: %s\n", ips); // prints "ip: 10.0.1.100"
1077
1078=over
1079
1080=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit
1081
1082=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit
1083
1084=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit
1085
1086=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit
1087
1088=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit
1089
1090=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit
1091
1092=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit
1093
1094=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit
1095
1096The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert
1097them to exactly I<N> digits, returning a pointer to the first character
1098after the digits. The I<value> must be in range. The functions marked with
1099I<32 bit> do their calculations internally in 32 bit, the ones marked with
1100I<64 bit> internally use 64 bit integers, which might be slow on 32 bit
1101architectures (the high level API decides on 32 vs. 64 bit versions using
1102C<ECB_64BIT_NATIVE>).
1103
1104=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit
1105
1106=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit
1107
1108=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit
1109
1110=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit
1111
1112=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit
1113
1114=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit
1115
1116=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit
1117
1118=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit
1119
1120Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value>
1121and convert them to at most I<N> digits, suppressing leading zeroes, and
1122returning a pointer to the first character after the digits.
1123
1124=item ECB_I2A_MAX_X5 (=59074)
1125
1126=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit
1127
1128=item ECB_I2A_MAX_X10 (=2932500665)
1129
1130=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit
1131
1132The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> >
1133functions, but they can generate one digit more, as long as the number
1134is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost
113516 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range),
1136respectively.
1137
1138For example, the digit part of a 32 bit signed integer just fits into the
1139C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10
1140digit number, it can convert all 32 bit signed numbers. Sadly, it's not
1141good enough for 32 bit unsigned numbers.
680 1142
681=back 1143=back
682 1144
683=head2 FLOATING POINT FIDDLING 1145=head2 FLOATING POINT FIDDLING
684 1146
685=over 4 1147=over
686 1148
687=item ECB_INFINITY 1149=item ECB_INFINITY [-UECB_NO_LIBM]
688 1150
689Evaluates to positive infinity if supported by the platform, otherwise to 1151Evaluates to positive infinity if supported by the platform, otherwise to
690a truly huge number. 1152a truly huge number.
691 1153
692=item ECB_NAN 1154=item ECB_NAN [-UECB_NO_LIBM]
693 1155
694Evaluates to a quiet NAN if supported by the platform, otherwise to 1156Evaluates to a quiet NAN if supported by the platform, otherwise to
695C<ECB_INFINITY>. 1157C<ECB_INFINITY>.
696 1158
697=item float ecb_ldexpf (float x, int exp) 1159=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM]
698 1160
699Same as C<ldexpf>, but always available. 1161Same as C<ldexpf>, but always available.
700 1162
1163=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM]
1164
701=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] 1165=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM]
702 1166
703=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] 1167=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM]
704 1168
705These functions each take an argument in the native C<float> or C<double> 1169These functions each take an argument in the native C<float> or C<double>
706type and return the IEEE 754 bit representation of it. 1170type and return the IEEE 754 bit representation of it (binary16/half,
1171binary32/single or binary64/double precision).
707 1172
708The bit representation is just as IEEE 754 defines it, i.e. the sign bit 1173The bit representation is just as IEEE 754 defines it, i.e. the sign bit
709will be the most significant bit, followed by exponent and mantissa. 1174will be the most significant bit, followed by exponent and mantissa.
710 1175
711This function should work even when the native floating point format isn't 1176This function should work even when the native floating point format isn't
715 1180
716On all modern platforms (where C<ECB_STDFP> is true), the compiler should 1181On all modern platforms (where C<ECB_STDFP> is true), the compiler should
717be able to optimise away this function completely. 1182be able to optimise away this function completely.
718 1183
719These functions can be helpful when serialising floats to the network - you 1184These functions can be helpful when serialising floats to the network - you
720can serialise the return value like a normal uint32_t/uint64_t. 1185can serialise the return value like a normal uint16_t/uint32_t/uint64_t.
721 1186
722Another use for these functions is to manipulate floating point values 1187Another use for these functions is to manipulate floating point values
723directly. 1188directly.
724 1189
725Silly example: toggle the sign bit of a float. 1190Silly example: toggle the sign bit of a float.
732 1197
733=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] 1198=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM]
734 1199
735=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] 1200=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM]
736 1201
737=item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] 1202=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM]
738 1203
739The reverse operation of the previous function - takes the bit 1204The reverse operation of the previous function - takes the bit
740representation of an IEEE binary16, binary32 or binary64 number and 1205representation of an IEEE binary16, binary32 or binary64 number (half,
741converts it to the native C<float> or C<double> format. 1206single or double precision) and converts it to the native C<float> or
1207C<double> format.
742 1208
743This function should work even when the native floating point format isn't 1209This function should work even when the native floating point format isn't
744IEEE compliant, of course at a speed and code size penalty, and of course 1210IEEE compliant, of course at a speed and code size penalty, and of course
745also within reasonable limits (it tries to convert normals and denormals, 1211also within reasonable limits (it tries to convert normals and denormals,
746and might be lucky for infinities, and with extraordinary luck, also for 1212and might be lucky for infinities, and with extraordinary luck, also for
747negative zero). 1213negative zero).
748 1214
749On all modern platforms (where C<ECB_STDFP> is true), the compiler should 1215On all modern platforms (where C<ECB_STDFP> is true), the compiler should
750be able to optimise away this function completely. 1216be able to optimise away this function completely.
751 1217
1218=item uint16_t ecb_binary32_to_binary16 (uint32_t x)
1219
1220=item uint32_t ecb_binary16_to_binary32 (uint16_t x)
1221
1222Convert a IEEE binary32/single precision to binary16/half format, and vice
1223versa, handling all details (round-to-nearest-even, subnormals, infinity
1224and NaNs) correctly.
1225
1226These are functions are available under C<-DECB_NO_LIBM>, since
1227they do not rely on the platform floating point format. The
1228C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are
1229usually what you want.
1230
752=back 1231=back
753 1232
754=head2 ARITHMETIC 1233=head2 ARITHMETIC
755 1234
756=over 4 1235=over
757 1236
758=item x = ecb_mod (m, n) 1237=item x = ecb_mod (m, n)
759 1238
760Returns C<m> modulo C<n>, which is the same as the positive remainder 1239Returns C<m> modulo C<n>, which is the same as the positive remainder
761of the division operation between C<m> and C<n>, using floored 1240of the division operation between C<m> and C<n>, using floored
768C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 1247C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
769negatable, that is, both C<m> and C<-m> must be representable in its 1248negatable, that is, both C<m> and C<-m> must be representable in its
770type (this typically excludes the minimum signed integer value, the same 1249type (this typically excludes the minimum signed integer value, the same
771limitation as for C</> and C<%> in C). 1250limitation as for C</> and C<%> in C).
772 1251
773Current GCC versions compile this into an efficient branchless sequence on 1252Current GCC/clang versions compile this into an efficient branchless
774almost all CPUs. 1253sequence on almost all CPUs.
775 1254
776For example, when you want to rotate forward through the members of an 1255For example, when you want to rotate forward through the members of an
777array for increasing C<m> (which might be negative), then you should use 1256array for increasing C<m> (which might be negative), then you should use
778C<ecb_mod>, as the C<%> operator might give either negative results, or 1257C<ecb_mod>, as the C<%> operator might give either negative results, or
779change direction for negative values: 1258change direction for negative values:
792 1271
793=back 1272=back
794 1273
795=head2 UTILITY 1274=head2 UTILITY
796 1275
797=over 4 1276=over
798 1277
799=item element_count = ecb_array_length (name) 1278=item element_count = ecb_array_length (name)
800 1279
801Returns the number of elements in the array C<name>. For example: 1280Returns the number of elements in the array C<name>. For example:
802 1281
810 1289
811=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF 1290=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF
812 1291
813These symbols need to be defined before including F<ecb.h> the first time. 1292These symbols need to be defined before including F<ecb.h> the first time.
814 1293
815=over 4 1294=over
816 1295
817=item ECB_NO_THREADS 1296=item ECB_NO_THREADS
818 1297
819If F<ecb.h> is never used from multiple threads, then this symbol can 1298If F<ecb.h> is never used from multiple threads, then this symbol can
820be defined, in which case memory fences (and similar constructs) are 1299be defined, in which case memory fences (and similar constructs) are
836dependencies on the math library (usually called F<-lm>) - these are 1315dependencies on the math library (usually called F<-lm>) - these are
837marked with [-UECB_NO_LIBM]. 1316marked with [-UECB_NO_LIBM].
838 1317
839=back 1318=back
840 1319
1320=head1 UNDOCUMENTED FUNCTIONALITY
841 1321
1322F<ecb.h> is full of undocumented functionality as well, some of which is
1323intended to be internal-use only, some of which we forgot to document, and
1324some of which we hide because we are not sure we will keep the interface
1325stable.
1326
1327While you are welcome to rummage around and use whatever you find useful
1328(we can't stop you), keep in mind that we will change undocumented
1329functionality in incompatible ways without thinking twice, while we are
1330considerably more conservative with documented things.
1331
1332=head1 AUTHORS
1333
1334C<libecb> is designed and maintained by:
1335
1336 Emanuele Giaquinta <e.giaquinta@glauco.it>
1337 Marc Alexander Lehmann <schmorp@schmorp.de>
1338
1339

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