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Revision 1.80 by root, Mon Jan 20 20:58:51 2020 UTC vs.
Revision 1.86 by root, Thu Apr 30 23:24:45 2020 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
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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
… …
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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723 725
724These 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
725all 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
726(C<ecb_rotl>). 728(C<ecb_rotl>).
727 729
728Current GCC versions understand these functions and usually compile them 730Current GCC/clang versions understand these functions and usually compile
729to "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>
730x86). 732on x86).
731 733
732=item T ecb_rotl (T x, unsigned int count) [C++] 734=item T ecb_rotl (T x, unsigned int count) [C++]
733 735
734=item T ecb_rotr (T x, unsigned int count) [C++] 736=item T ecb_rotr (T x, unsigned int count) [C++]
735 737
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786=item T ecb_le_to_host (T v) 788=item T ecb_le_to_host (T v)
787 789
788=item T ecb_host_to_be (T v) 790=item T ecb_host_to_be (T v)
789 791
790=item T ecb_host_to_le (T v) 792=item T ecb_host_to_le (T v)
793
794=back
791 795
792These functions work like their C counterparts, above, but use templates, 796These functions work like their C counterparts, above, but use templates,
793which make them useful in generic code. 797which make them useful in generic code.
794 798
795C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t> 799C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>
… …
1011C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 1015C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
1012negatable, that is, both C<m> and C<-m> must be representable in its 1016negatable, that is, both C<m> and C<-m> must be representable in its
1013type (this typically excludes the minimum signed integer value, the same 1017type (this typically excludes the minimum signed integer value, the same
1014limitation as for C</> and C<%> in C). 1018limitation as for C</> and C<%> in C).
1015 1019
1016Current GCC versions compile this into an efficient branchless sequence on 1020Current GCC/clang versions compile this into an efficient branchless
1017almost all CPUs. 1021sequence on almost all CPUs.
1018 1022
1019For example, when you want to rotate forward through the members of an 1023For example, when you want to rotate forward through the members of an
1020array for increasing C<m> (which might be negative), then you should use 1024array for increasing C<m> (which might be negative), then you should use
1021C<ecb_mod>, as the C<%> operator might give either negative results, or 1025C<ecb_mod>, as the C<%> operator might give either negative results, or
1022change direction for negative values: 1026change direction for negative values:

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