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Revision 1.85 by root, Mon Jan 20 21:13:38 2020 UTC

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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
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85=over 4 85=over 4
86 86
87=item ECB_C 87=item ECB_C
88 88
89True 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,
90while not claiming to be C++. 90while not claiming to be C++, i..e C, but not C++.
91 91
92=item ECB_C99 92=item ECB_C99
93 93
94True if the implementation claims to be compliant to C99 (ISO/IEC 94True if the implementation claims to be compliant to C99 (ISO/IEC
959899:1999) or any later version, while not claiming to be C++. 959899:1999) or any later version, while not claiming to be C++.
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110=item ECB_CPP11, ECB_CPP14, ECB_CPP17 110=item ECB_CPP11, ECB_CPP14, ECB_CPP17
111 111
112True if the implementation claims to be compliant to C++11/C++14/C++17 112True if the implementation claims to be compliant to C++11/C++14/C++17
113(ISO/IEC 14882:2011, :2014, :2017) or any later version. 113(ISO/IEC 14882:2011, :2014, :2017) or any later version.
114 114
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
115=item ECB_GCC_VERSION (major, minor) 124=item ECB_GCC_VERSION (major, minor)
116 125
117Expands to a true value (suitable for testing in by the preprocessor) 126Expands to a true value (suitable for testing by the preprocessor) if the
118if 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.
119higher.
120 128
121This 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
122compatible but aren't. 130compatible but aren't.
123 131
124=item ECB_EXTERN_C 132=item ECB_EXTERN_C
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143 151
144 ECB_EXTERN_C_END 152 ECB_EXTERN_C_END
145 153
146=item ECB_STDFP 154=item ECB_STDFP
147 155
148If this evaluates to a true value (suitable for testing in by the 156If this evaluates to a true value (suitable for testing by the
149preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 157preprocessor), then C<float> and C<double> use IEEE 754 single/binary32
150and double/binary64 representations internally I<and> the endianness of 158and double/binary64 representations internally I<and> the endianness of
151both 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>.
152 160
153This 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
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227=over 4 235=over 4
228 236
229=item ecb_unused 237=item ecb_unused
230 238
231Marks a function or a variable as "unused", which simply suppresses a 239Marks a function or a variable as "unused", which simply suppresses a
232warning by GCC when it detects it as unused. This is useful when you e.g. 240warning by the compiler when it detects it as unused. This is useful when
233declare a variable but do not always use it: 241you e.g. declare a variable but do not always use it:
234 242
235 { 243 {
236 ecb_unused int var; 244 ecb_unused int var;
237 245
238 #ifdef SOMECONDITION 246 #ifdef SOMECONDITION
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408 416
409=head2 OPTIMISATION HINTS 417=head2 OPTIMISATION HINTS
410 418
411=over 4 419=over 4
412 420
413=item ECB_OPTIMIZE_SIZE
414
415Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol
416can also be defined before including F<ecb.h>, in which case it will be
417unchanged.
418
419=item bool ecb_is_constant (expr) 421=item bool ecb_is_constant (expr)
420 422
421Returns true iff the expression can be deduced to be a compile-time 423Returns true iff the expression can be deduced to be a compile-time
422constant, and false otherwise. 424constant, and false otherwise.
423 425
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595 597
596=item int ecb_ctz32 (uint32_t x) 598=item int ecb_ctz32 (uint32_t x)
597 599
598=item int ecb_ctz64 (uint64_t x) 600=item int ecb_ctz64 (uint64_t x)
599 601
602=item int ecb_ctz (T x) [C++]
603
600Returns the index of the least significant bit set in C<x> (or 604Returns the index of the least significant bit set in C<x> (or
601equivalently the number of bits set to 0 before the least significant bit 605equivalently the number of bits set to 0 before the least significant bit
602set), starting from 0. If C<x> is 0 the result is undefined. 606set), starting from 0. If C<x> is 0 the result is undefined.
603 607
604For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. 608For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
605 609
610The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>,
611C<uint32_t> and C<uint64_t> types.
612
606For example: 613For example:
607 614
608 ecb_ctz32 (3) = 0 615 ecb_ctz32 (3) = 0
609 ecb_ctz32 (6) = 1 616 ecb_ctz32 (6) = 1
610 617
611=item bool ecb_is_pot32 (uint32_t x) 618=item bool ecb_is_pot32 (uint32_t x)
612 619
613=item bool ecb_is_pot64 (uint32_t x) 620=item bool ecb_is_pot64 (uint32_t x)
614 621
622=item bool ecb_is_pot (T x) [C++]
623
615Returns true iff C<x> is a power of two or C<x == 0>. 624Returns true iff C<x> is a power of two or C<x == 0>.
616 625
617For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>. 626For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>.
618 627
628The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>,
629C<uint32_t> and C<uint64_t> types.
630
619=item int ecb_ld32 (uint32_t x) 631=item int ecb_ld32 (uint32_t x)
620 632
621=item int ecb_ld64 (uint64_t x) 633=item int ecb_ld64 (uint64_t x)
634
635=item int ecb_ld64 (T x) [C++]
622 636
623Returns the index of the most significant bit set in C<x>, or the number 637Returns the index of the most significant bit set in C<x>, or the number
624of digits the number requires in binary (so that C<< 2**ld <= x < 638of digits the number requires in binary (so that C<< 2**ld <= x <
6252**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is 6392**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
626to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for 640to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
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631the given data type), while C<ecb_ld> returns how many bits the number 645the given data type), while C<ecb_ld> returns how many bits the number
632itself requires. 646itself requires.
633 647
634For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. 648For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
635 649
650The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>,
651C<uint32_t> and C<uint64_t> types.
652
636=item int ecb_popcount32 (uint32_t x) 653=item int ecb_popcount32 (uint32_t x)
637 654
638=item int ecb_popcount64 (uint64_t x) 655=item int ecb_popcount64 (uint64_t x)
639 656
657=item int ecb_popcount (T x) [C++]
658
640Returns the number of bits set to 1 in C<x>. 659Returns the number of bits set to 1 in C<x>.
641 660
642For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. 661For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
662
663The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>,
664C<uint32_t> and C<uint64_t> types.
643 665
644For example: 666For example:
645 667
646 ecb_popcount32 (7) = 3 668 ecb_popcount32 (7) = 3
647 ecb_popcount32 (255) = 8 669 ecb_popcount32 (255) = 8
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650 672
651=item uint16_t ecb_bitrev16 (uint16_t x) 673=item uint16_t ecb_bitrev16 (uint16_t x)
652 674
653=item uint32_t ecb_bitrev32 (uint32_t x) 675=item uint32_t ecb_bitrev32 (uint32_t x)
654 676
677=item T ecb_bitrev (T x) [C++]
678
655Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 679Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
656and so on. 680and so on.
657 681
682The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types.
683
658Example: 684Example:
659 685
660 ecb_bitrev8 (0xa7) = 0xea 686 ecb_bitrev8 (0xa7) = 0xea
661 ecb_bitrev32 (0xffcc4411) = 0x882233ff 687 ecb_bitrev32 (0xffcc4411) = 0x882233ff
662 688
689=item T ecb_bitrev (T x) [C++]
690
691Overloaded C++ bitrev function.
692
693C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>.
694
663=item uint32_t ecb_bswap16 (uint32_t x) 695=item uint32_t ecb_bswap16 (uint32_t x)
664 696
665=item uint32_t ecb_bswap32 (uint32_t x) 697=item uint32_t ecb_bswap32 (uint32_t x)
666 698
667=item uint64_t ecb_bswap64 (uint64_t x) 699=item uint64_t ecb_bswap64 (uint64_t x)
700
701=item T ecb_bswap (T x)
668 702
669These functions return the value of the 16-bit (32-bit, 64-bit) value 703These functions return the value of the 16-bit (32-bit, 64-bit) value
670C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in 704C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
671C<ecb_bswap32>). 705C<ecb_bswap32>).
672 706
673=item T ecb_bswap (T x) [C++] 707The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>,
674 708C<uint32_t> and C<uint64_t> types.
675For C++, an additional generic bswap function is provided. It supports
676C<uint8_t>, C<uint16_t>, C<uint32_t> and C<uint64_t>.
677 709
678=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) 710=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
679 711
680=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) 712=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
681 713
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693 725
694These two families of functions return the value of C<x> after rotating 726These two families of functions return the value of C<x> after rotating
695all the bits by C<count> positions to the right (C<ecb_rotr>) or left 727all the bits by C<count> positions to the right (C<ecb_rotr>) or left
696(C<ecb_rotl>). 728(C<ecb_rotl>).
697 729
698Current GCC versions understand these functions and usually compile them 730Current GCC/clang versions understand these functions and usually compile
699to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on 731them to "optimal" code (e.g. a single C<rol> or a combination of C<shld>
700x86). 732on x86).
733
734=item T ecb_rotl (T x, unsigned int count) [C++]
735
736=item T ecb_rotr (T x, unsigned int count) [C++]
737
738Overloaded C++ rotl/rotr functions.
739
740C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
701 741
702=back 742=back
703 743
704=head2 HOST ENDIANNESS CONVERSION 744=head2 HOST ENDIANNESS CONVERSION
705 745
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718=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v) 758=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v)
719 759
720Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order. 760Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order.
721 761
722The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>, 762The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>,
723where be and le stand for big endian and little endian, respectively. 763where C<be> and C<le> stand for big endian and little endian, respectively.
724 764
725=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v) 765=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v)
726 766
727=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v) 767=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v)
728 768
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737Like above, but converts I<from> host byte order to the specified 777Like above, but converts I<from> host byte order to the specified
738endianness. 778endianness.
739 779
740=back 780=back
741 781
742In C++ the following additional functions are supported: 782In C++ the following additional template functions are supported:
743 783
744=over 4 784=over 4
745 785
746=item T ecb_be_to_host (T v) 786=item T ecb_be_to_host (T v)
747 787
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749 789
750=item T ecb_host_to_be (T v) 790=item T ecb_host_to_be (T v)
751 791
752=item T ecb_host_to_le (T v) 792=item T ecb_host_to_le (T v)
753 793
754These work like their C counterparts, above, but use templates for the 794These functions work like their C counterparts, above, but use templates,
755type, which make them useful in generic code. 795which make them useful in generic code.
756 796
757C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t> 797C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
758(so unlike their C counterparts, there is a version for C<uint8_t>, which 798(so unlike their C counterparts, there is a version for C<uint8_t>, which
759again can be useful in generic code). 799again can be useful in generic code).
760 800
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812Like above, but additionally convert from host byte order to big endian 852Like above, but additionally convert from host byte order to big endian
813(C<be>) or little endian (C<le>) byte order while doing so. 853(C<be>) or little endian (C<le>) byte order while doing so.
814 854
815=back 855=back
816 856
817In C++ the following additional functions are supported: 857In C++ the following additional template functions are supported:
818 858
819=over 4 859=over 4
820 860
821=item T ecb_peek (const void *ptr) 861=item T ecb_peek<T> (const void *ptr)
822 862
823=item T ecb_peek_be (const void *ptr) 863=item T ecb_peek_be<T> (const void *ptr)
824 864
825=item T ecb_peek_le (const void *ptr) 865=item T ecb_peek_le<T> (const void *ptr)
826 866
827=item T ecb_peek_u (const void *ptr) 867=item T ecb_peek_u<T> (const void *ptr)
828 868
829=item T ecb_peek_be_u (const void *ptr) 869=item T ecb_peek_be_u<T> (const void *ptr)
830 870
831=item T ecb_peek_le_u (const void *ptr) 871=item T ecb_peek_le_u<T> (const void *ptr)
832 872
833Similarly to their C counterparts, these functions load an unsigned 8, 16, 873Similarly to their C counterparts, these functions load an unsigned 8, 16,
83432 or 64 bit value from memory, with optional conversion from big/little 87432 or 64 bit value from memory, with optional conversion from big/little
835endian. 875endian.
836 876
837Since the type cannot be deduced, it has top be specified explicitly, e.g. 877Since the type cannot be deduced, it has to be specified explicitly, e.g.
838 878
839 uint_fast16_t v = ecb_peek<uint16_t> (ptr); 879 uint_fast16_t v = ecb_peek<uint16_t> (ptr);
840 880
841C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. 881C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>.
842 882
… …
973C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 1013C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
974negatable, that is, both C<m> and C<-m> must be representable in its 1014negatable, that is, both C<m> and C<-m> must be representable in its
975type (this typically excludes the minimum signed integer value, the same 1015type (this typically excludes the minimum signed integer value, the same
976limitation as for C</> and C<%> in C). 1016limitation as for C</> and C<%> in C).
977 1017
978Current GCC versions compile this into an efficient branchless sequence on 1018Current GCC/clang versions compile this into an efficient branchless
979almost all CPUs. 1019sequence on almost all CPUs.
980 1020
981For example, when you want to rotate forward through the members of an 1021For example, when you want to rotate forward through the members of an
982array for increasing C<m> (which might be negative), then you should use 1022array for increasing C<m> (which might be negative), then you should use
983C<ecb_mod>, as the C<%> operator might give either negative results, or 1023C<ecb_mod>, as the C<%> operator might give either negative results, or
984change direction for negative values: 1024change direction for negative values:

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