… | |
… | |
10 | |
10 | |
11 | Its homepage can be found here: |
11 | Its homepage can be found here: |
12 | |
12 | |
13 | http://software.schmorp.de/pkg/libecb |
13 | http://software.schmorp.de/pkg/libecb |
14 | |
14 | |
15 | It mainly provides a number of wrappers around GCC built-ins, together |
15 | It mainly provides a number of wrappers around many compiler built-ins, |
16 | with replacement functions for other compilers. In addition to this, |
16 | together with replacement functions for other compilers. In addition |
17 | it provides a number of other lowlevel C utilities, such as endianness |
17 | to this, it provides a number of other lowlevel C utilities, such as |
18 | detection, byte swapping or bit rotations. |
18 | endianness detection, byte swapping or bit rotations. |
19 | |
19 | |
20 | Or in other words, things that should be built into any standard C system, |
20 | Or in other words, things that should be built into any standard C |
21 | but aren't, implemented as efficient as possible with GCC, and still |
21 | system, but aren't, implemented as efficient as possible with GCC (clang, |
22 | correct with other compilers. |
22 | msvc...), and still correct with other compilers. |
23 | |
23 | |
24 | More might come. |
24 | More might come. |
25 | |
25 | |
26 | =head2 ABOUT THE HEADER |
26 | =head2 ABOUT THE HEADER |
27 | |
27 | |
… | |
… | |
80 | |
80 | |
81 | All the following symbols expand to an expression that can be tested in |
81 | All the following symbols expand to an expression that can be tested in |
82 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
82 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
83 | ensure it's either C<0> or C<1> if you need that). |
83 | ensure it's either C<0> or C<1> if you need that). |
84 | |
84 | |
85 | =over 4 |
85 | =over |
86 | |
86 | |
87 | =item ECB_C |
87 | =item ECB_C |
88 | |
88 | |
89 | True if the implementation defines the C<__STDC__> macro to a true value, |
89 | True if the implementation defines the C<__STDC__> macro to a true value, |
90 | while not claiming to be C++. |
90 | while not claiming to be C++, i..e C, but not C++. |
91 | |
91 | |
92 | =item ECB_C99 |
92 | =item ECB_C99 |
93 | |
93 | |
94 | True if the implementation claims to be compliant to C99 (ISO/IEC |
94 | True if the implementation claims to be compliant to C99 (ISO/IEC |
95 | 9899:1999) or any later version, while not claiming to be C++. |
95 | 9899:1999) or any later version, while not claiming to be C++. |
… | |
… | |
110 | =item ECB_CPP11, ECB_CPP14, ECB_CPP17 |
110 | =item ECB_CPP11, ECB_CPP14, ECB_CPP17 |
111 | |
111 | |
112 | True if the implementation claims to be compliant to C++11/C++14/C++17 |
112 | True 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 | |
|
|
115 | Note that many C++20 features will likely have their own feature test |
|
|
116 | macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>). |
|
|
117 | |
|
|
118 | =item ECB_OPTIMIZE_SIZE |
|
|
119 | |
|
|
120 | Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol |
|
|
121 | can also be defined before including F<ecb.h>, in which case it will be |
|
|
122 | unchanged. |
|
|
123 | |
115 | =item ECB_GCC_VERSION (major, minor) |
124 | =item ECB_GCC_VERSION (major, minor) |
116 | |
125 | |
117 | Expands to a true value (suitable for testing in by the preprocessor) |
126 | Expands to a true value (suitable for testing by the preprocessor) if the |
118 | if the compiler used is GNU C and the version is the given version, or |
127 | compiler used is GNU C and the version is the given version, or higher. |
119 | higher. |
|
|
120 | |
128 | |
121 | This macro tries to return false on compilers that claim to be GCC |
129 | This macro tries to return false on compilers that claim to be GCC |
122 | compatible but aren't. |
130 | compatible 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 | |
148 | If this evaluates to a true value (suitable for testing in by the |
156 | If this evaluates to a true value (suitable for testing by the |
149 | preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
157 | preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
150 | and double/binary64 representations internally I<and> the endianness of |
158 | and double/binary64 representations internally I<and> the endianness of |
151 | both types match the endianness of C<uint32_t> and C<uint64_t>. |
159 | both types match the endianness of C<uint32_t> and C<uint64_t>. |
152 | |
160 | |
153 | This means you can just copy the bits of a C<float> (or C<double>) to an |
161 | This means you can just copy the bits of a C<float> (or C<double>) to an |
… | |
… | |
155 | without having to think about format or endianness. |
163 | without having to think about format or endianness. |
156 | |
164 | |
157 | This is true for basically all modern platforms, although F<ecb.h> might |
165 | This is true for basically all modern platforms, although F<ecb.h> might |
158 | not be able to deduce this correctly everywhere and might err on the safe |
166 | not be able to deduce this correctly everywhere and might err on the safe |
159 | side. |
167 | side. |
|
|
168 | |
|
|
169 | =item ECB_64BIT_NATIVE |
|
|
170 | |
|
|
171 | Evaluates to a true value (suitable for both preprocessor and C code |
|
|
172 | testing) if 64 bit integer types on this architecture are evaluated |
|
|
173 | "natively", that is, with similar speeds as 32 bit integers. While 64 bit |
|
|
174 | integer support is very common (and in fact required by libecb), 32 bit |
|
|
175 | cpus have to emulate operations on them, so you might want to avoid them. |
160 | |
176 | |
161 | =item ECB_AMD64, ECB_AMD64_X32 |
177 | =item ECB_AMD64, ECB_AMD64_X32 |
162 | |
178 | |
163 | These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
179 | These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
164 | ABI, respectively, and undefined elsewhere. |
180 | ABI, respectively, and undefined elsewhere. |
… | |
… | |
171 | |
187 | |
172 | =back |
188 | =back |
173 | |
189 | |
174 | =head2 MACRO TRICKERY |
190 | =head2 MACRO TRICKERY |
175 | |
191 | |
176 | =over 4 |
192 | =over |
177 | |
193 | |
178 | =item ECB_CONCAT (a, b) |
194 | =item ECB_CONCAT (a, b) |
179 | |
195 | |
180 | Expands any macros in C<a> and C<b>, then concatenates the result to form |
196 | Expands any macros in C<a> and C<b>, then concatenates the result to form |
181 | a single token. This is mainly useful to form identifiers from components, |
197 | a single token. This is mainly useful to form identifiers from components, |
… | |
… | |
222 | declarations must be put before the whole declaration: |
238 | declarations must be put before the whole declaration: |
223 | |
239 | |
224 | ecb_const int mysqrt (int a); |
240 | ecb_const int mysqrt (int a); |
225 | ecb_unused int i; |
241 | ecb_unused int i; |
226 | |
242 | |
227 | =over 4 |
243 | =over |
228 | |
244 | |
229 | =item ecb_unused |
245 | =item ecb_unused |
230 | |
246 | |
231 | Marks a function or a variable as "unused", which simply suppresses a |
247 | Marks a function or a variable as "unused", which simply suppresses a |
232 | warning by GCC when it detects it as unused. This is useful when you e.g. |
248 | warning by the compiler when it detects it as unused. This is useful when |
233 | declare a variable but do not always use it: |
249 | you e.g. declare a variable but do not always use it: |
234 | |
250 | |
235 | { |
251 | { |
236 | ecb_unused int var; |
252 | ecb_unused int var; |
237 | |
253 | |
238 | #ifdef SOMECONDITION |
254 | #ifdef SOMECONDITION |
… | |
… | |
406 | |
422 | |
407 | =back |
423 | =back |
408 | |
424 | |
409 | =head2 OPTIMISATION HINTS |
425 | =head2 OPTIMISATION HINTS |
410 | |
426 | |
411 | =over 4 |
427 | =over |
412 | |
|
|
413 | =item ECB_OPTIMIZE_SIZE |
|
|
414 | |
|
|
415 | Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol |
|
|
416 | can also be defined before including F<ecb.h>, in which case it will be |
|
|
417 | unchanged. |
|
|
418 | |
428 | |
419 | =item bool ecb_is_constant (expr) |
429 | =item bool ecb_is_constant (expr) |
420 | |
430 | |
421 | Returns true iff the expression can be deduced to be a compile-time |
431 | Returns true iff the expression can be deduced to be a compile-time |
422 | constant, and false otherwise. |
432 | constant, and false otherwise. |
… | |
… | |
579 | |
589 | |
580 | =back |
590 | =back |
581 | |
591 | |
582 | =head2 BIT FIDDLING / BIT WIZARDRY |
592 | =head2 BIT FIDDLING / BIT WIZARDRY |
583 | |
593 | |
584 | =over 4 |
594 | =over |
585 | |
595 | |
586 | =item bool ecb_big_endian () |
596 | =item bool ecb_big_endian () |
587 | |
597 | |
588 | =item bool ecb_little_endian () |
598 | =item bool ecb_little_endian () |
589 | |
599 | |
… | |
… | |
721 | |
731 | |
722 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
732 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
723 | |
733 | |
724 | These two families of functions return the value of C<x> after rotating |
734 | These two families of functions return the value of C<x> after rotating |
725 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
735 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
726 | (C<ecb_rotl>). |
736 | (C<ecb_rotl>). There are no restrictions on the value C<count>, i.e. both |
|
|
737 | zero and values equal or larger than the word width work correctly. |
727 | |
738 | |
728 | Current GCC versions understand these functions and usually compile them |
739 | Current GCC/clang versions understand these functions and usually compile |
729 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
740 | them to "optimal" code (e.g. a single C<rol> or a combination of C<shld> |
730 | x86). |
741 | on x86). |
731 | |
742 | |
732 | =item T ecb_rotl (T x, unsigned int count) [C++] |
743 | =item T ecb_rotl (T x, unsigned int count) [C++] |
733 | |
744 | |
734 | =item T ecb_rotr (T x, unsigned int count) [C++] |
745 | =item T ecb_rotr (T x, unsigned int count) [C++] |
735 | |
746 | |
… | |
… | |
739 | |
750 | |
740 | =back |
751 | =back |
741 | |
752 | |
742 | =head2 HOST ENDIANNESS CONVERSION |
753 | =head2 HOST ENDIANNESS CONVERSION |
743 | |
754 | |
744 | =over 4 |
755 | =over |
745 | |
756 | |
746 | =item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v) |
757 | =item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v) |
747 | |
758 | |
748 | =item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v) |
759 | =item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v) |
749 | |
760 | |
… | |
… | |
777 | |
788 | |
778 | =back |
789 | =back |
779 | |
790 | |
780 | In C++ the following additional template functions are supported: |
791 | In C++ the following additional template functions are supported: |
781 | |
792 | |
782 | =over 4 |
793 | =over |
783 | |
794 | |
784 | =item T ecb_be_to_host (T v) |
795 | =item T ecb_be_to_host (T v) |
785 | |
796 | |
786 | =item T ecb_le_to_host (T v) |
797 | =item T ecb_le_to_host (T v) |
787 | |
798 | |
788 | =item T ecb_host_to_be (T v) |
799 | =item T ecb_host_to_be (T v) |
789 | |
800 | |
790 | =item T ecb_host_to_le (T v) |
801 | =item T ecb_host_to_le (T v) |
|
|
802 | |
|
|
803 | =back |
791 | |
804 | |
792 | These functions work like their C counterparts, above, but use templates, |
805 | These functions work like their C counterparts, above, but use templates, |
793 | which make them useful in generic code. |
806 | which make them useful in generic code. |
794 | |
807 | |
795 | C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t> |
808 | C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t> |
… | |
… | |
798 | |
811 | |
799 | =head2 UNALIGNED LOAD/STORE |
812 | =head2 UNALIGNED LOAD/STORE |
800 | |
813 | |
801 | These function load or store unaligned multi-byte values. |
814 | These function load or store unaligned multi-byte values. |
802 | |
815 | |
803 | =over 4 |
816 | =over |
804 | |
817 | |
805 | =item uint_fast16_t ecb_peek_u16_u (const void *ptr) |
818 | =item uint_fast16_t ecb_peek_u16_u (const void *ptr) |
806 | |
819 | |
807 | =item uint_fast32_t ecb_peek_u32_u (const void *ptr) |
820 | =item uint_fast32_t ecb_peek_u32_u (const void *ptr) |
808 | |
821 | |
… | |
… | |
852 | |
865 | |
853 | =back |
866 | =back |
854 | |
867 | |
855 | In C++ the following additional template functions are supported: |
868 | In C++ the following additional template functions are supported: |
856 | |
869 | |
857 | =over 4 |
870 | =over |
858 | |
871 | |
859 | =item T ecb_peek<T> (const void *ptr) |
872 | =item T ecb_peek<T> (const void *ptr) |
860 | |
873 | |
861 | =item T ecb_peek_be<T> (const void *ptr) |
874 | =item T ecb_peek_be<T> (const void *ptr) |
862 | |
875 | |
… | |
… | |
904 | (C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
917 | (C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
905 | all of which hopefully makes them more useful in generic code. |
918 | all of which hopefully makes them more useful in generic code. |
906 | |
919 | |
907 | =back |
920 | =back |
908 | |
921 | |
|
|
922 | =head2 FAST INTEGER TO STRING |
|
|
923 | |
|
|
924 | Libecb defines a set of very fast integer to decimal string (or integer |
|
|
925 | to ascii, short C<i2a>) functions. These work by converting the integer |
|
|
926 | to a fixed point representation and then successively multiplying out |
|
|
927 | the topmost digits. Unlike some other, also very fast, libraries, ecb's |
|
|
928 | algorithm should be completely branchless per digit, and does not rely on |
|
|
929 | the presence of special cpu functions (such as clz). |
|
|
930 | |
|
|
931 | There is a high level API that takes an C<int32_t>, C<uint32_t>, |
|
|
932 | C<int64_t> or C<uint64_t> as argument, and a low-level API, which is |
|
|
933 | harder to use but supports slightly more formatting options. |
|
|
934 | |
|
|
935 | =head3 HIGH LEVEL API |
|
|
936 | |
|
|
937 | The high level API consists of four functions, one each for C<int32_t>, |
|
|
938 | C<uint32_t>, C<int64_t> and C<uint64_t>: |
|
|
939 | |
|
|
940 | Example: |
|
|
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 | |
|
|
953 | Takes an C<uint32_t> I<value> and formats it as a decimal number starting |
|
|
954 | at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a |
|
|
955 | pointer to just after the generated string, where you would normally put |
|
|
956 | the terminating C<0> character. This function outputs the minimum number |
|
|
957 | of digits. |
|
|
958 | |
|
|
959 | =item ECB_I2A_U32_DIGITS (=10) |
|
|
960 | |
|
|
961 | =item char *ecb_i2a_i32 (char *ptr, int32_t value) |
|
|
962 | |
|
|
963 | Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus |
|
|
964 | sign 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 | |
|
|
974 | Similar to their 32 bit counterparts, these take a 64 bit argument. |
|
|
975 | |
|
|
976 | =item ECB_I2A_MAX_DIGITS (=21) |
|
|
977 | |
|
|
978 | Instead of using a type specific length macro, youi can just use |
|
|
979 | C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function. |
|
|
980 | |
|
|
981 | =back |
|
|
982 | |
|
|
983 | =head3 LOW-LEVEL API |
|
|
984 | |
|
|
985 | The functions above use a number of low-level APIs which have some strict |
|
|
986 | limitations, but can be used as building blocks (study of C<ecb_i2a_i32> |
|
|
987 | and related functions is recommended). |
|
|
988 | |
|
|
989 | There are three families of functions: functions that convert a number |
|
|
990 | to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0> |
|
|
991 | for "leading zeroes"), functions that generate up to N digits, skipping |
|
|
992 | leading zeroes (C<_N>), and functions that can generate more digits, but |
|
|
993 | the leading digit has limited range (C<_xN>). |
|
|
994 | |
|
|
995 | None of the functions deal with negative numbers. |
|
|
996 | |
|
|
997 | Example: 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 | |
|
|
1026 | The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert |
|
|
1027 | them to exactly I<N> digits, returning a pointer to the first character |
|
|
1028 | after the digits. The I<value> must be in range. The functions marked with |
|
|
1029 | I<32 bit> do their calculations internally in 32 bit, the ones marked with |
|
|
1030 | I<64 bit> internally use 64 bit integers, which might be slow on 32 bit |
|
|
1031 | architectures (the high level API decides on 32 vs. 64 bit versions using |
|
|
1032 | C<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 | |
|
|
1050 | Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value> |
|
|
1051 | and convert them to at most I<N> digits, suppressing leading zeroes, and |
|
|
1052 | returning 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 | |
|
|
1062 | The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> > |
|
|
1063 | functions, but they can generate one digit more, as long as the number |
|
|
1064 | is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost |
|
|
1065 | 16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range), |
|
|
1066 | respectively. |
|
|
1067 | |
|
|
1068 | For example, the digit part of a 32 bit signed integer just fits into the |
|
|
1069 | C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10 |
|
|
1070 | digit number, it can convert all 32 bit signed numbers. Sadly, it's not |
|
|
1071 | good enough for 32 bit unsigned numbers. |
|
|
1072 | |
|
|
1073 | =back |
|
|
1074 | |
909 | =head2 FLOATING POINT FIDDLING |
1075 | =head2 FLOATING POINT FIDDLING |
910 | |
1076 | |
911 | =over 4 |
1077 | =over |
912 | |
1078 | |
913 | =item ECB_INFINITY [-UECB_NO_LIBM] |
1079 | =item ECB_INFINITY [-UECB_NO_LIBM] |
914 | |
1080 | |
915 | Evaluates to positive infinity if supported by the platform, otherwise to |
1081 | Evaluates to positive infinity if supported by the platform, otherwise to |
916 | a truly huge number. |
1082 | a truly huge number. |
… | |
… | |
994 | |
1160 | |
995 | =back |
1161 | =back |
996 | |
1162 | |
997 | =head2 ARITHMETIC |
1163 | =head2 ARITHMETIC |
998 | |
1164 | |
999 | =over 4 |
1165 | =over |
1000 | |
1166 | |
1001 | =item x = ecb_mod (m, n) |
1167 | =item x = ecb_mod (m, n) |
1002 | |
1168 | |
1003 | Returns C<m> modulo C<n>, which is the same as the positive remainder |
1169 | Returns C<m> modulo C<n>, which is the same as the positive remainder |
1004 | of the division operation between C<m> and C<n>, using floored |
1170 | of the division operation between C<m> and C<n>, using floored |
… | |
… | |
1011 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
1177 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
1012 | negatable, that is, both C<m> and C<-m> must be representable in its |
1178 | negatable, that is, both C<m> and C<-m> must be representable in its |
1013 | type (this typically excludes the minimum signed integer value, the same |
1179 | type (this typically excludes the minimum signed integer value, the same |
1014 | limitation as for C</> and C<%> in C). |
1180 | limitation as for C</> and C<%> in C). |
1015 | |
1181 | |
1016 | Current GCC versions compile this into an efficient branchless sequence on |
1182 | Current GCC/clang versions compile this into an efficient branchless |
1017 | almost all CPUs. |
1183 | sequence on almost all CPUs. |
1018 | |
1184 | |
1019 | For example, when you want to rotate forward through the members of an |
1185 | For example, when you want to rotate forward through the members of an |
1020 | array for increasing C<m> (which might be negative), then you should use |
1186 | array for increasing C<m> (which might be negative), then you should use |
1021 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
1187 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
1022 | change direction for negative values: |
1188 | change direction for negative values: |
… | |
… | |
1035 | |
1201 | |
1036 | =back |
1202 | =back |
1037 | |
1203 | |
1038 | =head2 UTILITY |
1204 | =head2 UTILITY |
1039 | |
1205 | |
1040 | =over 4 |
1206 | =over |
1041 | |
1207 | |
1042 | =item element_count = ecb_array_length (name) |
1208 | =item element_count = ecb_array_length (name) |
1043 | |
1209 | |
1044 | Returns the number of elements in the array C<name>. For example: |
1210 | Returns the number of elements in the array C<name>. For example: |
1045 | |
1211 | |
… | |
… | |
1053 | |
1219 | |
1054 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
1220 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
1055 | |
1221 | |
1056 | These symbols need to be defined before including F<ecb.h> the first time. |
1222 | These symbols need to be defined before including F<ecb.h> the first time. |
1057 | |
1223 | |
1058 | =over 4 |
1224 | =over |
1059 | |
1225 | |
1060 | =item ECB_NO_THREADS |
1226 | =item ECB_NO_THREADS |
1061 | |
1227 | |
1062 | If F<ecb.h> is never used from multiple threads, then this symbol can |
1228 | If F<ecb.h> is never used from multiple threads, then this symbol can |
1063 | be defined, in which case memory fences (and similar constructs) are |
1229 | be defined, in which case memory fences (and similar constructs) are |