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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 | |
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58 | |
58 | |
59 | =head2 TYPES / TYPE SUPPORT |
59 | =head2 TYPES / TYPE SUPPORT |
60 | |
60 | |
61 | ecb.h makes sure that the following types are defined (in the expected way): |
61 | ecb.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 |
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65 | int32_t uint32_ |
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66 | int64_t uint64_t |
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67 | int_fast8_t uint_fast8_t |
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68 | int_fast16_t uint_fast16_t |
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69 | int_fast32_t uint_fast32_t |
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70 | int_fast64_t uint_fast64_t |
65 | intptr_t uintptr_t |
71 | intptr_t uintptr_t |
66 | |
72 | |
67 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
73 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
74 | platform (currently C<4> or C<8>) and can be used in preprocessor |
69 | expressions. |
75 | expressions. |
70 | |
76 | |
71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
77 | For 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 | |
75 | 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 |
76 | 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 |
77 | 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). |
78 | |
84 | |
79 | =over 4 |
85 | =over |
80 | |
86 | |
81 | =item ECB_C |
87 | =item ECB_C |
82 | |
88 | |
83 | 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, |
84 | while not claiming to be C++. |
90 | while not claiming to be C++, i..e C, but not C++. |
85 | |
91 | |
86 | =item ECB_C99 |
92 | =item ECB_C99 |
87 | |
93 | |
88 | 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 |
89 | 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++. |
90 | |
96 | |
91 | Note that later versions (ECB_C11) remove core features again (for |
97 | Note that later versions (ECB_C11) remove core features again (for |
92 | example, variable length arrays). |
98 | example, variable length arrays). |
93 | |
99 | |
94 | =item ECB_C11 |
100 | =item ECB_C11, ECB_C17 |
95 | |
101 | |
96 | True if the implementation claims to be compliant to C11 (ISO/IEC |
102 | True if the implementation claims to be compliant to C11/C17 (ISO/IEC |
97 | 9899:2011) or any later version, while not claiming to be C++. |
103 | 9899:2011, :20187) or any later version, while not claiming to be C++. |
98 | |
104 | |
99 | =item ECB_CPP |
105 | =item ECB_CPP |
100 | |
106 | |
101 | True if the implementation defines the C<__cplusplus__> macro to a true |
107 | True if the implementation defines the C<__cplusplus__> macro to a true |
102 | value, which is typically true for C++ compilers. |
108 | value, which is typically true for C++ compilers. |
103 | |
109 | |
104 | =item ECB_CPP11 |
110 | =item ECB_CPP11, ECB_CPP14, ECB_CPP17 |
105 | |
111 | |
106 | True if the implementation claims to be compliant to ISO/IEC 14882:2011 |
112 | True 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. |
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114 | |
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115 | Note that many C++20 features will likely have their own feature test |
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116 | macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>). |
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117 | |
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118 | =item ECB_OPTIMIZE_SIZE |
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119 | |
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120 | Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol |
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121 | can also be defined before including F<ecb.h>, in which case it will be |
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122 | unchanged. |
108 | |
123 | |
109 | =item ECB_GCC_VERSION (major, minor) |
124 | =item ECB_GCC_VERSION (major, minor) |
110 | |
125 | |
111 | 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 |
112 | 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. |
113 | higher. |
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114 | |
128 | |
115 | 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 |
116 | compatible but aren't. |
130 | compatible but aren't. |
117 | |
131 | |
118 | =item ECB_EXTERN_C |
132 | =item ECB_EXTERN_C |
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137 | |
151 | |
138 | ECB_EXTERN_C_END |
152 | ECB_EXTERN_C_END |
139 | |
153 | |
140 | =item ECB_STDFP |
154 | =item ECB_STDFP |
141 | |
155 | |
142 | 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 |
143 | 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 |
144 | and double/binary64 representations internally I<and> the endianness of |
158 | and double/binary64 representations internally I<and> the endianness of |
145 | 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>. |
146 | |
160 | |
147 | 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 |
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149 | without having to think about format or endianness. |
163 | without having to think about format or endianness. |
150 | |
164 | |
151 | 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 |
152 | 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 |
153 | side. |
167 | side. |
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168 | |
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169 | =item ECB_64BIT_NATIVE |
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170 | |
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171 | Evaluates to a true value (suitable for both preprocessor and C code |
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172 | testing) if 64 bit integer types on this architecture are evaluated |
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173 | "natively", that is, with similar speeds as 32 bit integers. While 64 bit |
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174 | integer support is very common (and in fact required by libecb), 32 bit |
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175 | cpus 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 | |
157 | 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 |
158 | ABI, respectively, and undefined elsewhere. |
180 | ABI, respectively, and undefined elsewhere. |
… | |
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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 | |
174 | 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 |
175 | 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, |
… | |
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186 | it. This is mainly useful to get the contents of a macro in string form, |
208 | it. This is mainly useful to get the contents of a macro in string form, |
187 | e.g.: |
209 | e.g.: |
188 | |
210 | |
189 | #define SQL_LIMIT 100 |
211 | #define SQL_LIMIT 100 |
190 | sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); |
212 | sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); |
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213 | |
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214 | =item ECB_STRINGIFY_EXPR (expr) |
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215 | |
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216 | Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it |
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217 | is a valid expression. This is useful to catch typos or cases where the |
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218 | macro isn't available: |
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219 | |
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220 | #include <errno.h> |
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221 | |
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222 | ECB_STRINGIFY (EDOM); // "33" (on my system at least) |
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223 | ECB_STRINGIFY_EXPR (EDOM); // "33" |
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224 | |
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225 | // now imagine we had a typo: |
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226 | |
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227 | ECB_STRINGIFY (EDAM); // "EDAM" |
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228 | ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined |
191 | |
229 | |
192 | =back |
230 | =back |
193 | |
231 | |
194 | =head2 ATTRIBUTES |
232 | =head2 ATTRIBUTES |
195 | |
233 | |
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200 | declarations must be put before the whole declaration: |
238 | declarations must be put before the whole declaration: |
201 | |
239 | |
202 | ecb_const int mysqrt (int a); |
240 | ecb_const int mysqrt (int a); |
203 | ecb_unused int i; |
241 | ecb_unused int i; |
204 | |
242 | |
205 | =over 4 |
243 | =over |
206 | |
244 | |
207 | =item ecb_unused |
245 | =item ecb_unused |
208 | |
246 | |
209 | 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 |
210 | 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 |
211 | declare a variable but do not always use it: |
249 | you e.g. declare a variable but do not always use it: |
212 | |
250 | |
213 | { |
251 | { |
214 | ecb_unused int var; |
252 | ecb_unused int var; |
215 | |
253 | |
216 | #ifdef SOMECONDITION |
254 | #ifdef SOMECONDITION |
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226 | Similar to C<ecb_unused>, but marks a function, variable or type as |
264 | Similar to C<ecb_unused>, but marks a function, variable or type as |
227 | deprecated. This makes some compilers warn when the type is used. |
265 | deprecated. This makes some compilers warn when the type is used. |
228 | |
266 | |
229 | =item ecb_deprecated_message (message) |
267 | =item ecb_deprecated_message (message) |
230 | |
268 | |
231 | Same as C<ecb_deprecated>, but if possible, supply a diagnostic that is |
269 | Same as C<ecb_deprecated>, but if possible, the specified diagnostic is |
232 | used instead of a generic depreciation message when the object is being |
270 | used instead of a generic depreciation message when the object is being |
233 | used. |
271 | used. |
234 | |
272 | |
235 | =item ecb_inline |
273 | =item ecb_inline |
236 | |
274 | |
237 | Expands either to C<static inline> or to just C<static>, if inline |
275 | Expands either to (a compiler-specific equivalent of) C<static inline> or |
238 | isn't supported. It should be used to declare functions that should be |
276 | to just C<static>, if inline isn't supported. It should be used to declare |
239 | inlined, for code size or speed reasons. |
277 | functions that should be inlined, for code size or speed reasons. |
240 | |
278 | |
241 | Example: inline this function, it surely will reduce codesize. |
279 | Example: inline this function, it surely will reduce codesize. |
242 | |
280 | |
243 | ecb_inline int |
281 | ecb_inline int |
244 | negmul (int a, int b) |
282 | negmul (int a, int b) |
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246 | return - (a * b); |
284 | return - (a * b); |
247 | } |
285 | } |
248 | |
286 | |
249 | =item ecb_noinline |
287 | =item ecb_noinline |
250 | |
288 | |
251 | Prevent a function from being inlined - it might be optimised away, but |
289 | Prevents a function from being inlined - it might be optimised away, but |
252 | not inlined into other functions. This is useful if you know your function |
290 | not inlined into other functions. This is useful if you know your function |
253 | is rarely called and large enough for inlining not to be helpful. |
291 | is rarely called and large enough for inlining not to be helpful. |
254 | |
292 | |
255 | =item ecb_noreturn |
293 | =item ecb_noreturn |
256 | |
294 | |
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384 | |
422 | |
385 | =back |
423 | =back |
386 | |
424 | |
387 | =head2 OPTIMISATION HINTS |
425 | =head2 OPTIMISATION HINTS |
388 | |
426 | |
389 | =over 4 |
427 | =over |
390 | |
428 | |
391 | =item bool ecb_is_constant (expr) |
429 | =item bool ecb_is_constant (expr) |
392 | |
430 | |
393 | 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 |
394 | constant, and false otherwise. |
432 | constant, and false otherwise. |
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473 | real_reserve_method (size); /* presumably noinline */ |
511 | real_reserve_method (size); /* presumably noinline */ |
474 | } |
512 | } |
475 | |
513 | |
476 | =item ecb_assume (cond) |
514 | =item ecb_assume (cond) |
477 | |
515 | |
478 | Try to tell the compiler that some condition is true, even if it's not |
516 | Tries to tell the compiler that some condition is true, even if it's not |
479 | obvious. |
517 | obvious. This is not a function, but a statement: it cannot be used in |
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518 | another expression. |
480 | |
519 | |
481 | This can be used to teach the compiler about invariants or other |
520 | This can be used to teach the compiler about invariants or other |
482 | conditions that might improve code generation, but which are impossible to |
521 | conditions that might improve code generation, but which are impossible to |
483 | deduce form the code itself. |
522 | deduce form the code itself. |
484 | |
523 | |
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505 | |
544 | |
506 | =item ecb_unreachable () |
545 | =item ecb_unreachable () |
507 | |
546 | |
508 | This function does nothing itself, except tell the compiler that it will |
547 | This function does nothing itself, except tell the compiler that it will |
509 | never be executed. Apart from suppressing a warning in some cases, this |
548 | never be executed. Apart from suppressing a warning in some cases, this |
510 | function can be used to implement C<ecb_assume> or similar functions. |
549 | function can be used to implement C<ecb_assume> or similar functionality. |
511 | |
550 | |
512 | =item ecb_prefetch (addr, rw, locality) |
551 | =item ecb_prefetch (addr, rw, locality) |
513 | |
552 | |
514 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
553 | Tells the compiler to try to prefetch memory at the given C<addr>ess |
515 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
554 | for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
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517 | the data will likely be accessed very often, and values in between mean |
556 | the data will likely be accessed very often, and values in between mean |
518 | something... in between. The memory pointed to by the address does not |
557 | something... in between. The memory pointed to by the address does not |
519 | need to be accessible (it could be a null pointer for example), but C<rw> |
558 | need to be accessible (it could be a null pointer for example), but C<rw> |
520 | and C<locality> must be compile-time constants. |
559 | and C<locality> must be compile-time constants. |
521 | |
560 | |
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561 | This is a statement, not a function: you cannot use it as part of an |
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562 | expression. |
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563 | |
522 | An obvious way to use this is to prefetch some data far away, in a big |
564 | An obvious way to use this is to prefetch some data far away, in a big |
523 | array you loop over. This prefetches memory some 128 array elements later, |
565 | array you loop over. This prefetches memory some 128 array elements later, |
524 | in the hope that it will be ready when the CPU arrives at that location. |
566 | in the hope that it will be ready when the CPU arrives at that location. |
525 | |
567 | |
526 | int sum = 0; |
568 | int sum = 0; |
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… | |
547 | |
589 | |
548 | =back |
590 | =back |
549 | |
591 | |
550 | =head2 BIT FIDDLING / BIT WIZARDRY |
592 | =head2 BIT FIDDLING / BIT WIZARDRY |
551 | |
593 | |
552 | =over 4 |
594 | =over |
553 | |
595 | |
554 | =item bool ecb_big_endian () |
596 | =item bool ecb_big_endian () |
555 | |
597 | |
556 | =item bool ecb_little_endian () |
598 | =item bool ecb_little_endian () |
557 | |
599 | |
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563 | |
605 | |
564 | =item int ecb_ctz32 (uint32_t x) |
606 | =item int ecb_ctz32 (uint32_t x) |
565 | |
607 | |
566 | =item int ecb_ctz64 (uint64_t x) |
608 | =item int ecb_ctz64 (uint64_t x) |
567 | |
609 | |
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610 | =item int ecb_ctz (T x) [C++] |
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611 | |
568 | Returns the index of the least significant bit set in C<x> (or |
612 | Returns the index of the least significant bit set in C<x> (or |
569 | equivalently the number of bits set to 0 before the least significant bit |
613 | equivalently the number of bits set to 0 before the least significant bit |
570 | set), starting from 0. If C<x> is 0 the result is undefined. |
614 | set), starting from 0. If C<x> is 0 the result is undefined. |
571 | |
615 | |
572 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
616 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
573 | |
617 | |
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618 | The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>, |
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619 | C<uint32_t> and C<uint64_t> types. |
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620 | |
574 | For example: |
621 | For example: |
575 | |
622 | |
576 | ecb_ctz32 (3) = 0 |
623 | ecb_ctz32 (3) = 0 |
577 | ecb_ctz32 (6) = 1 |
624 | ecb_ctz32 (6) = 1 |
578 | |
625 | |
579 | =item bool ecb_is_pot32 (uint32_t x) |
626 | =item bool ecb_is_pot32 (uint32_t x) |
580 | |
627 | |
581 | =item bool ecb_is_pot64 (uint32_t x) |
628 | =item bool ecb_is_pot64 (uint32_t x) |
582 | |
629 | |
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630 | =item bool ecb_is_pot (T x) [C++] |
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631 | |
583 | Return true iff C<x> is a power of two or C<x == 0>. |
632 | Returns true iff C<x> is a power of two or C<x == 0>. |
584 | |
633 | |
585 | For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. |
634 | For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>. |
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635 | |
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636 | The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>, |
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637 | C<uint32_t> and C<uint64_t> types. |
586 | |
638 | |
587 | =item int ecb_ld32 (uint32_t x) |
639 | =item int ecb_ld32 (uint32_t x) |
588 | |
640 | |
589 | =item int ecb_ld64 (uint64_t x) |
641 | =item int ecb_ld64 (uint64_t x) |
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642 | |
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643 | =item int ecb_ld64 (T x) [C++] |
590 | |
644 | |
591 | Returns the index of the most significant bit set in C<x>, or the number |
645 | Returns the index of the most significant bit set in C<x>, or the number |
592 | of digits the number requires in binary (so that C<< 2**ld <= x < |
646 | of digits the number requires in binary (so that C<< 2**ld <= x < |
593 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
647 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
594 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
648 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
… | |
… | |
599 | the given data type), while C<ecb_ld> returns how many bits the number |
653 | the given data type), while C<ecb_ld> returns how many bits the number |
600 | itself requires. |
654 | itself requires. |
601 | |
655 | |
602 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
656 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
603 | |
657 | |
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658 | The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>, |
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659 | C<uint32_t> and C<uint64_t> types. |
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660 | |
604 | =item int ecb_popcount32 (uint32_t x) |
661 | =item int ecb_popcount32 (uint32_t x) |
605 | |
662 | |
606 | =item int ecb_popcount64 (uint64_t x) |
663 | =item int ecb_popcount64 (uint64_t x) |
607 | |
664 | |
|
|
665 | =item int ecb_popcount (T x) [C++] |
|
|
666 | |
608 | Returns the number of bits set to 1 in C<x>. |
667 | Returns the number of bits set to 1 in C<x>. |
609 | |
668 | |
610 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
669 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
|
|
670 | |
|
|
671 | The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>, |
|
|
672 | C<uint32_t> and C<uint64_t> types. |
611 | |
673 | |
612 | For example: |
674 | For example: |
613 | |
675 | |
614 | ecb_popcount32 (7) = 3 |
676 | ecb_popcount32 (7) = 3 |
615 | ecb_popcount32 (255) = 8 |
677 | ecb_popcount32 (255) = 8 |
… | |
… | |
618 | |
680 | |
619 | =item uint16_t ecb_bitrev16 (uint16_t x) |
681 | =item uint16_t ecb_bitrev16 (uint16_t x) |
620 | |
682 | |
621 | =item uint32_t ecb_bitrev32 (uint32_t x) |
683 | =item uint32_t ecb_bitrev32 (uint32_t x) |
622 | |
684 | |
|
|
685 | =item T ecb_bitrev (T x) [C++] |
|
|
686 | |
623 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
687 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
624 | and so on. |
688 | and so on. |
625 | |
689 | |
|
|
690 | The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types. |
|
|
691 | |
626 | Example: |
692 | Example: |
627 | |
693 | |
628 | ecb_bitrev8 (0xa7) = 0xea |
694 | ecb_bitrev8 (0xa7) = 0xea |
629 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
695 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
630 | |
696 | |
|
|
697 | =item T ecb_bitrev (T x) [C++] |
|
|
698 | |
|
|
699 | Overloaded C++ bitrev function. |
|
|
700 | |
|
|
701 | C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>. |
|
|
702 | |
631 | =item uint32_t ecb_bswap16 (uint32_t x) |
703 | =item uint32_t ecb_bswap16 (uint32_t x) |
632 | |
704 | |
633 | =item uint32_t ecb_bswap32 (uint32_t x) |
705 | =item uint32_t ecb_bswap32 (uint32_t x) |
634 | |
706 | |
635 | =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) |
636 | |
710 | |
637 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
711 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
638 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
712 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
639 | C<ecb_bswap32>). |
713 | C<ecb_bswap32>). |
640 | |
714 | |
|
|
715 | The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>, |
|
|
716 | C<uint32_t> and C<uint64_t> types. |
|
|
717 | |
641 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
718 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
642 | |
719 | |
643 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
720 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
644 | |
721 | |
645 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
722 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
… | |
… | |
654 | |
731 | |
655 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
732 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
656 | |
733 | |
657 | 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 |
658 | 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 |
659 | (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. Also, |
|
|
738 | notwithstanding C<count> being unsigned, negative numbers work and shift |
|
|
739 | to the opposite direction. |
660 | |
740 | |
661 | Current GCC versions understand these functions and usually compile them |
741 | Current GCC/clang versions understand these functions and usually compile |
662 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
742 | them to "optimal" code (e.g. a single C<rol> or a combination of C<shld> |
663 | x86). |
743 | on 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 | |
|
|
749 | Overloaded C++ rotl/rotr functions. |
|
|
750 | |
|
|
751 | C<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 | |
|
|
757 | Sometimes you have an integer and want to distribute its bits well, for |
|
|
758 | example, to use it as a hash in a hashtable. A common example is pointer |
|
|
759 | values, which often only have a limited range (e.g. low and high bits are |
|
|
760 | often zero). |
|
|
761 | |
|
|
762 | The following functions try to mix the bits to get a good bias-free |
|
|
763 | distribution. They were mainly made for pointers, but the underlying |
|
|
764 | integer functions are exposed as well. |
|
|
765 | |
|
|
766 | As an added benefit, the functions are reversible, so if you find it |
|
|
767 | convenient to store only the hash value, you can recover the original |
|
|
768 | pointer 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 |
|
|
770 | functions for other bit widths). |
|
|
771 | |
|
|
772 | The unmix functions are very slightly slower than the mix functions, so |
|
|
773 | it is equally very slightly preferable to store the original values wehen |
|
|
774 | convenient. |
|
|
775 | |
|
|
776 | The underlying algorithm if subject to change, so currently these |
|
|
777 | functions are not suitable for persistent hash tables, as their result |
|
|
778 | value can change between diferent versions of libecb. |
|
|
779 | |
|
|
780 | =over |
|
|
781 | |
|
|
782 | =item uintptr_t ecb_ptrmix (void *ptr) |
|
|
783 | |
|
|
784 | Mixes the bits of a pointer so the result is suitable for hash table |
|
|
785 | lookups. In other words, this hashes the pointer value. |
|
|
786 | |
|
|
787 | =item uintptr_t ecb_ptrmix (T *ptr) [C++] |
|
|
788 | |
|
|
789 | Overload the C<ecb_ptrmix> function to work for any pointer in C++. |
|
|
790 | |
|
|
791 | =item void *ecb_ptrunmix (uintptr_t v) |
|
|
792 | |
|
|
793 | Unmix the hash value into the original pointer. This only works as long |
|
|
794 | as the hash value is not truncated, i.e. you used C<uintptr_t> (or |
|
|
795 | equivalent) throughout to store it. |
|
|
796 | |
|
|
797 | =item T *ecb_ptrunmix<T> (uintptr_t v) [C++] |
|
|
798 | |
|
|
799 | The somewhat less useful template version of C<ecb_ptrunmix> for |
|
|
800 | C++. 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 | |
|
|
810 | Sometimes you don't have a pointer but an integer whose values are very |
|
|
811 | badly distributed. In this case you cna sue these integer versions of the |
|
|
812 | mixing 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 | |
|
|
818 | The reverse of the C<ecb_mix> functions - they take a mixed/hashed value |
|
|
819 | and 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 | |
|
|
839 | Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order. |
|
|
840 | |
|
|
841 | The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>, |
|
|
842 | where 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 | |
|
|
856 | Like above, but converts I<from> host byte order to the specified |
|
|
857 | endianness. |
|
|
858 | |
|
|
859 | =back |
|
|
860 | |
|
|
861 | In 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 | |
|
|
875 | These functions work like their C counterparts, above, but use templates, |
|
|
876 | which make them useful in generic code. |
|
|
877 | |
|
|
878 | C<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 |
|
|
880 | again can be useful in generic code). |
|
|
881 | |
|
|
882 | =head2 UNALIGNED LOAD/STORE |
|
|
883 | |
|
|
884 | These 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 | |
|
|
894 | These functions load an unaligned, unsigned 16, 32 or 64 bit value from |
|
|
895 | memory. |
|
|
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 | |
|
|
909 | Like above, but additionally convert from big endian (C<be>) or little |
|
|
910 | endian (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 | |
|
|
918 | These functions store an unaligned, unsigned 16, 32 or 64 bit value to |
|
|
919 | memory. |
|
|
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 | |
|
|
933 | Like 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 | |
|
|
938 | In 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 | |
|
|
954 | Similarly to their C counterparts, these functions load an unsigned 8, 16, |
|
|
955 | 32 or 64 bit value from memory, with optional conversion from big/little |
|
|
956 | endian. |
|
|
957 | |
|
|
958 | Since 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 | |
|
|
962 | C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. |
|
|
963 | |
|
|
964 | Unlike their C counterparts, these functions support 8 bit quantities |
|
|
965 | (C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
|
|
966 | all 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 | |
|
|
980 | Again, similarly to their C counterparts, these functions store an |
|
|
981 | unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to |
|
|
982 | big/little endian. |
|
|
983 | |
|
|
984 | C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. |
|
|
985 | |
|
|
986 | Unlike their C counterparts, these functions support 8 bit quantities |
|
|
987 | (C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
|
|
988 | all of which hopefully makes them more useful in generic code. |
|
|
989 | |
|
|
990 | =back |
|
|
991 | |
|
|
992 | =head2 FAST INTEGER TO STRING |
|
|
993 | |
|
|
994 | Libecb defines a set of very fast integer to decimal string (or integer |
|
|
995 | to ascii, short C<i2a>) functions. These work by converting the integer |
|
|
996 | to a fixed point representation and then successively multiplying out |
|
|
997 | the topmost digits. Unlike some other, also very fast, libraries, ecb's |
|
|
998 | algorithm should be completely branchless per digit, and does not rely on |
|
|
999 | the presence of special cpu functions (such as clz). |
|
|
1000 | |
|
|
1001 | There is a high level API that takes an C<int32_t>, C<uint32_t>, |
|
|
1002 | C<int64_t> or C<uint64_t> as argument, and a low-level API, which is |
|
|
1003 | harder to use but supports slightly more formatting options. |
|
|
1004 | |
|
|
1005 | =head3 HIGH LEVEL API |
|
|
1006 | |
|
|
1007 | The high level API consists of four functions, one each for C<int32_t>, |
|
|
1008 | C<uint32_t>, C<int64_t> and C<uint64_t>: |
|
|
1009 | |
|
|
1010 | Example: |
|
|
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 | |
|
|
1023 | Takes an C<uint32_t> I<value> and formats it as a decimal number starting |
|
|
1024 | at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a |
|
|
1025 | pointer to just after the generated string, where you would normally put |
|
|
1026 | the terminating C<0> character. This function outputs the minimum number |
|
|
1027 | of digits. |
|
|
1028 | |
|
|
1029 | =item ECB_I2A_U32_DIGITS (=10) |
|
|
1030 | |
|
|
1031 | =item char *ecb_i2a_i32 (char *ptr, int32_t value) |
|
|
1032 | |
|
|
1033 | Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus |
|
|
1034 | sign 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 | |
|
|
1044 | Similar to their 32 bit counterparts, these take a 64 bit argument. |
|
|
1045 | |
|
|
1046 | =item ECB_I2A_MAX_DIGITS (=21) |
|
|
1047 | |
|
|
1048 | Instead of using a type specific length macro, you can just use |
|
|
1049 | C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function. |
|
|
1050 | |
|
|
1051 | =back |
|
|
1052 | |
|
|
1053 | =head3 LOW-LEVEL API |
|
|
1054 | |
|
|
1055 | The functions above use a number of low-level APIs which have some strict |
|
|
1056 | limitations, but can be used as building blocks (studying C<ecb_i2a_i32> |
|
|
1057 | and related functions is recommended). |
|
|
1058 | |
|
|
1059 | There are three families of functions: functions that convert a number |
|
|
1060 | to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0> |
|
|
1061 | for "leading zeroes"), functions that generate up to N digits, skipping |
|
|
1062 | leading zeroes (C<_N>), and functions that can generate more digits, but |
|
|
1063 | the leading digit has limited range (C<_xN>). |
|
|
1064 | |
|
|
1065 | None of the functions deal with negative numbers. |
|
|
1066 | |
|
|
1067 | Example: 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 | |
|
|
1096 | The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert |
|
|
1097 | them to exactly I<N> digits, returning a pointer to the first character |
|
|
1098 | after the digits. The I<value> must be in range. The functions marked with |
|
|
1099 | I<32 bit> do their calculations internally in 32 bit, the ones marked with |
|
|
1100 | I<64 bit> internally use 64 bit integers, which might be slow on 32 bit |
|
|
1101 | architectures (the high level API decides on 32 vs. 64 bit versions using |
|
|
1102 | C<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 | |
|
|
1120 | Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value> |
|
|
1121 | and convert them to at most I<N> digits, suppressing leading zeroes, and |
|
|
1122 | returning 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 | |
|
|
1132 | The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> > |
|
|
1133 | functions, but they can generate one digit more, as long as the number |
|
|
1134 | is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost |
|
|
1135 | 16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range), |
|
|
1136 | respectively. |
|
|
1137 | |
|
|
1138 | For example, the digit part of a 32 bit signed integer just fits into the |
|
|
1139 | C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10 |
|
|
1140 | digit number, it can convert all 32 bit signed numbers. Sadly, it's not |
|
|
1141 | good enough for 32 bit unsigned numbers. |
664 | |
1142 | |
665 | =back |
1143 | =back |
666 | |
1144 | |
667 | =head2 FLOATING POINT FIDDLING |
1145 | =head2 FLOATING POINT FIDDLING |
668 | |
1146 | |
669 | =over 4 |
1147 | =over |
670 | |
1148 | |
671 | =item ECB_INFINITY |
1149 | =item ECB_INFINITY [-UECB_NO_LIBM] |
672 | |
1150 | |
673 | Evaluates to positive infinity if supported by the platform, otherwise to |
1151 | Evaluates to positive infinity if supported by the platform, otherwise to |
674 | a truly huge number. |
1152 | a truly huge number. |
675 | |
1153 | |
676 | =item ECB_NON |
1154 | =item ECB_NAN [-UECB_NO_LIBM] |
677 | |
1155 | |
678 | Evaluates to a quiet NAN if supported by the platform, otherwise to |
1156 | Evaluates to a quiet NAN if supported by the platform, otherwise to |
679 | C<ECB_INFINITY>. |
1157 | C<ECB_INFINITY>. |
680 | |
1158 | |
681 | =item float ecb_ldexpf (float x, int exp) |
1159 | =item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM] |
682 | |
1160 | |
683 | Same as C<ldexpf>, but always available. |
1161 | Same as C<ldexpf>, but always available. |
684 | |
1162 | |
|
|
1163 | =item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM] |
|
|
1164 | |
685 | =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] |
686 | |
1166 | |
687 | =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] |
688 | |
1168 | |
689 | These functions each take an argument in the native C<float> or C<double> |
1169 | These functions each take an argument in the native C<float> or C<double> |
690 | type and return the IEEE 754 bit representation of it. |
1170 | type and return the IEEE 754 bit representation of it (binary16/half, |
|
|
1171 | binary32/single or binary64/double precision). |
691 | |
1172 | |
692 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
1173 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
693 | will be the most significant bit, followed by exponent and mantissa. |
1174 | will be the most significant bit, followed by exponent and mantissa. |
694 | |
1175 | |
695 | This function should work even when the native floating point format isn't |
1176 | This function should work even when the native floating point format isn't |
696 | IEEE compliant, of course at a speed and code size penalty, and of course |
1177 | IEEE compliant, of course at a speed and code size penalty, and of course |
697 | also within reasonable limits (it tries to convert NaNs, infinities and |
1178 | also within reasonable limits (it tries to convert NaNs, infinities and |
698 | denormals, but will likely convert negative zero to positive zero). |
1179 | denormals, but will likely convert negative zero to positive zero). |
699 | |
1180 | |
700 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
1181 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
701 | be able to optimise away this function completely. |
1182 | be able to completely optimise away the 32 and 64 bit functions. |
702 | |
1183 | |
703 | These functions can be helpful when serialising floats to the network - you |
1184 | These functions can be helpful when serialising floats to the network - you |
704 | can serialise the return value like a normal uint32_t/uint64_t. |
1185 | can serialise the return value like a normal uint16_t/uint32_t/uint64_t. |
705 | |
1186 | |
706 | Another use for these functions is to manipulate floating point values |
1187 | Another use for these functions is to manipulate floating point values |
707 | directly. |
1188 | directly. |
708 | |
1189 | |
709 | Silly example: toggle the sign bit of a float. |
1190 | Silly example: toggle the sign bit of a float. |
… | |
… | |
716 | |
1197 | |
717 | =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] |
718 | |
1199 | |
719 | =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] |
720 | |
1201 | |
721 | =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] |
722 | |
1203 | |
723 | The reverse operation of the previous function - takes the bit |
1204 | The reverse operation of the previous function - takes the bit |
724 | representation of an IEEE binary16, binary32 or binary64 number and |
1205 | representation of an IEEE binary16, binary32 or binary64 number (half, |
725 | converts it to the native C<float> or C<double> format. |
1206 | single or double precision) and converts it to the native C<float> or |
|
|
1207 | C<double> format. |
726 | |
1208 | |
727 | This function should work even when the native floating point format isn't |
1209 | This function should work even when the native floating point format isn't |
728 | IEEE compliant, of course at a speed and code size penalty, and of course |
1210 | IEEE compliant, of course at a speed and code size penalty, and of course |
729 | also within reasonable limits (it tries to convert normals and denormals, |
1211 | also within reasonable limits (it tries to convert normals and denormals, |
730 | and might be lucky for infinities, and with extraordinary luck, also for |
1212 | and might be lucky for infinities, and with extraordinary luck, also for |
731 | negative zero). |
1213 | negative zero). |
732 | |
1214 | |
733 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
1215 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
734 | be able to optimise away this function completely. |
1216 | be able to optimise away this function completely. |
735 | |
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 | |
|
|
1222 | Convert a IEEE binary32/single precision to binary16/half format, and vice |
|
|
1223 | versa, handling all details (round-to-nearest-even, subnormals, infinity |
|
|
1224 | and NaNs) correctly. |
|
|
1225 | |
|
|
1226 | These are functions are available under C<-DECB_NO_LIBM>, since |
|
|
1227 | they do not rely on the platform floating point format. The |
|
|
1228 | C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are |
|
|
1229 | usually what you want. |
|
|
1230 | |
736 | =back |
1231 | =back |
737 | |
1232 | |
738 | =head2 ARITHMETIC |
1233 | =head2 ARITHMETIC |
739 | |
1234 | |
740 | =over 4 |
1235 | =over |
741 | |
1236 | |
742 | =item x = ecb_mod (m, n) |
1237 | =item x = ecb_mod (m, n) |
743 | |
1238 | |
744 | Returns C<m> modulo C<n>, which is the same as the positive remainder |
1239 | Returns C<m> modulo C<n>, which is the same as the positive remainder |
745 | of the division operation between C<m> and C<n>, using floored |
1240 | of the division operation between C<m> and C<n>, using floored |
… | |
… | |
752 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
1247 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
753 | negatable, that is, both C<m> and C<-m> must be representable in its |
1248 | negatable, that is, both C<m> and C<-m> must be representable in its |
754 | type (this typically excludes the minimum signed integer value, the same |
1249 | type (this typically excludes the minimum signed integer value, the same |
755 | limitation as for C</> and C<%> in C). |
1250 | limitation as for C</> and C<%> in C). |
756 | |
1251 | |
757 | Current GCC versions compile this into an efficient branchless sequence on |
1252 | Current GCC/clang versions compile this into an efficient branchless |
758 | almost all CPUs. |
1253 | sequence on almost all CPUs. |
759 | |
1254 | |
760 | For example, when you want to rotate forward through the members of an |
1255 | For example, when you want to rotate forward through the members of an |
761 | array for increasing C<m> (which might be negative), then you should use |
1256 | array for increasing C<m> (which might be negative), then you should use |
762 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
1257 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
763 | change direction for negative values: |
1258 | change direction for negative values: |
… | |
… | |
776 | |
1271 | |
777 | =back |
1272 | =back |
778 | |
1273 | |
779 | =head2 UTILITY |
1274 | =head2 UTILITY |
780 | |
1275 | |
781 | =over 4 |
1276 | =over |
782 | |
1277 | |
783 | =item element_count = ecb_array_length (name) |
1278 | =item element_count = ecb_array_length (name) |
784 | |
1279 | |
785 | Returns the number of elements in the array C<name>. For example: |
1280 | Returns the number of elements in the array C<name>. For example: |
786 | |
1281 | |
… | |
… | |
794 | |
1289 | |
795 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
1290 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
796 | |
1291 | |
797 | These symbols need to be defined before including F<ecb.h> the first time. |
1292 | These symbols need to be defined before including F<ecb.h> the first time. |
798 | |
1293 | |
799 | =over 4 |
1294 | =over |
800 | |
1295 | |
801 | =item ECB_NO_THREADS |
1296 | =item ECB_NO_THREADS |
802 | |
1297 | |
803 | If F<ecb.h> is never used from multiple threads, then this symbol can |
1298 | If F<ecb.h> is never used from multiple threads, then this symbol can |
804 | be defined, in which case memory fences (and similar constructs) are |
1299 | be defined, in which case memory fences (and similar constructs) are |
… | |
… | |
820 | dependencies on the math library (usually called F<-lm>) - these are |
1315 | dependencies on the math library (usually called F<-lm>) - these are |
821 | marked with [-UECB_NO_LIBM]. |
1316 | marked with [-UECB_NO_LIBM]. |
822 | |
1317 | |
823 | =back |
1318 | =back |
824 | |
1319 | |
|
|
1320 | =head1 UNDOCUMENTED FUNCTIONALITY |
825 | |
1321 | |
|
|
1322 | F<ecb.h> is full of undocumented functionality as well, some of which is |
|
|
1323 | intended to be internal-use only, some of which we forgot to document, and |
|
|
1324 | some of which we hide because we are not sure we will keep the interface |
|
|
1325 | stable. |
|
|
1326 | |
|
|
1327 | While you are welcome to rummage around and use whatever you find useful |
|
|
1328 | (we don't want to stop you), keep in mind that we will change undocumented |
|
|
1329 | functionality in incompatible ways without thinking twice, while we are |
|
|
1330 | considerably more conservative with documented things. |
|
|
1331 | |
|
|
1332 | =head1 AUTHORS |
|
|
1333 | |
|
|
1334 | C<libecb> is designed and maintained by: |
|
|
1335 | |
|
|
1336 | Emanuele Giaquinta <e.giaquinta@glauco.it> |
|
|
1337 | Marc Alexander Lehmann <schmorp@schmorp.de> |