… | |
… | |
54 | only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
54 | only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
55 | the corresponding function relies on C to implement the correct types, and |
55 | the corresponding function relies on C to implement the correct types, and |
56 | is usually implemented as a macro. Specifically, a "bool" in this manual |
56 | is usually implemented as a macro. Specifically, a "bool" in this manual |
57 | refers to any kind of boolean value, not a specific type. |
57 | refers to any kind of boolean value, not a specific type. |
58 | |
58 | |
|
|
59 | =head2 TYPES / TYPE SUPPORT |
|
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60 | |
|
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61 | ecb.h makes sure that the following types are defined (in the expected way): |
|
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62 | |
|
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63 | int8_t uint8_t int16_t uint16_t |
|
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64 | int32_t uint32_t int64_t uint64_t |
|
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65 | intptr_t uintptr_t |
|
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66 | |
|
|
67 | The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
|
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68 | platform (currently C<4> or C<8>) and can be used in preprocessor |
|
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69 | expressions. |
|
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70 | |
|
|
71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
|
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72 | |
|
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73 | =head2 LANGUAGE/COMPILER VERSIONS |
|
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74 | |
|
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75 | All the following symbols expand to an expression that can be tested in |
|
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76 | preprocessor instructions as well as treated as a boolean (use C<!!> to |
|
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77 | ensure it's either C<0> or C<1> if you need that). |
|
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78 | |
|
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79 | =over 4 |
|
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80 | |
|
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81 | =item ECB_C |
|
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82 | |
|
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83 | True if the implementation defines the C<__STDC__> macro to a true value, |
|
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84 | while not claiming to be C++. |
|
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85 | |
|
|
86 | =item ECB_C99 |
|
|
87 | |
|
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88 | 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++. |
|
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90 | |
|
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91 | Note that later versions (ECB_C11) remove core features again (for |
|
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92 | example, variable length arrays). |
|
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93 | |
|
|
94 | =item ECB_C11 |
|
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95 | |
|
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96 | True if the implementation claims to be compliant to C11 (ISO/IEC |
|
|
97 | 9899:2011) or any later version, while not claiming to be C++. |
|
|
98 | |
|
|
99 | =item ECB_CPP |
|
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100 | |
|
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101 | True if the implementation defines the C<__cplusplus__> macro to a true |
|
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102 | value, which is typically true for C++ compilers. |
|
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103 | |
|
|
104 | =item ECB_CPP11 |
|
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105 | |
|
|
106 | True if the implementation claims to be compliant to ISO/IEC 14882:2011 |
|
|
107 | (C++11) or any later version. |
|
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108 | |
|
|
109 | =item ECB_GCC_VERSION (major, minor) |
|
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110 | |
|
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111 | Expands to a true value (suitable for testing in by the preprocessor) |
|
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112 | if the compiler used is GNU C and the version is the given version, or |
|
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113 | higher. |
|
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114 | |
|
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115 | This macro tries to return false on compilers that claim to be GCC |
|
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116 | compatible but aren't. |
|
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117 | |
|
|
118 | =item ECB_EXTERN_C |
|
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119 | |
|
|
120 | Expands to C<extern "C"> in C++, and a simple C<extern> in C. |
|
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121 | |
|
|
122 | This can be used to declare a single external C function: |
|
|
123 | |
|
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124 | ECB_EXTERN_C int printf (const char *format, ...); |
|
|
125 | |
|
|
126 | =item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END |
|
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127 | |
|
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128 | These two macros can be used to wrap multiple C<extern "C"> definitions - |
|
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129 | they expand to nothing in C. |
|
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130 | |
|
|
131 | They are most useful in header files: |
|
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132 | |
|
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133 | ECB_EXTERN_C_BEG |
|
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134 | |
|
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135 | int mycfun1 (int x); |
|
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136 | int mycfun2 (int x); |
|
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137 | |
|
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138 | ECB_EXTERN_C_END |
|
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139 | |
|
|
140 | =item ECB_STDFP |
|
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141 | |
|
|
142 | If this evaluates to a true value (suitable for testing in by the |
|
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143 | preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
|
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144 | and double/binary64 representations internally I<and> the endianness of |
|
|
145 | both types match the endianness of C<uint32_t> and C<uint64_t>. |
|
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146 | |
|
|
147 | This means you can just copy the bits of a C<float> (or C<double>) to an |
|
|
148 | C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation |
|
|
149 | without having to think about format or endianness. |
|
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150 | |
|
|
151 | This is true for basically all modern platforms, although F<ecb.h> might |
|
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152 | not be able to deduce this correctly everywhere and might err on the safe |
|
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153 | side. |
|
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154 | |
|
|
155 | =item ECB_AMD64, ECB_AMD64_X32 |
|
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156 | |
|
|
157 | These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
|
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158 | ABI, respectively, and undefined elsewhere. |
|
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159 | |
|
|
160 | The designers of the new X32 ABI for some inexplicable reason decided to |
|
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161 | make it look exactly like amd64, even though it's completely incompatible |
|
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162 | to that ABI, breaking about every piece of software that assumed that |
|
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163 | C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
|
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164 | necessary. |
|
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165 | |
|
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166 | =back |
|
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167 | |
59 | =head2 GCC ATTRIBUTES |
168 | =head2 GCC ATTRIBUTES |
60 | |
169 | |
61 | A major part of libecb deals with GCC attributes. These are additional |
170 | A major part of libecb deals with GCC attributes. These are additional |
62 | attributes that you can assign to functions, variables and sometimes even |
171 | attributes that you can assign to functions, variables and sometimes even |
63 | types - much like C<const> or C<volatile> in C. |
172 | types - much like C<const> or C<volatile> in C. |
… | |
… | |
76 | |
185 | |
77 | =over 4 |
186 | =over 4 |
78 | |
187 | |
79 | =item ecb_attribute ((attrs...)) |
188 | =item ecb_attribute ((attrs...)) |
80 | |
189 | |
81 | A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to |
190 | A simple wrapper that expands to C<__attribute__((attrs))> on GCC 3.1+ and |
82 | nothing on other compilers, so the effect is that only GCC sees these. |
191 | Clang 2.8+, and to nothing on other compilers, so the effect is that only |
|
|
192 | GCC and Clang see these. |
83 | |
193 | |
84 | Example: use the C<deprecated> attribute on a function. |
194 | Example: use the C<deprecated> attribute on a function. |
85 | |
195 | |
86 | ecb_attribute((__deprecated__)) void |
196 | ecb_attribute((__deprecated__)) void |
87 | do_not_use_me_anymore (void); |
197 | do_not_use_me_anymore (void); |
… | |
… | |
101 | #else |
211 | #else |
102 | return 0; |
212 | return 0; |
103 | #endif |
213 | #endif |
104 | } |
214 | } |
105 | |
215 | |
|
|
216 | =item ecb_deprecated |
|
|
217 | |
|
|
218 | Similar to C<ecb_unused>, but marks a function, variable or type as |
|
|
219 | deprecated. This makes some compilers warn when the type is used. |
|
|
220 | |
|
|
221 | =item ecb_inline |
|
|
222 | |
|
|
223 | This is not actually an attribute, but you use it like one. It expands |
|
|
224 | either to C<static inline> or to just C<static>, if inline isn't |
|
|
225 | supported. It should be used to declare functions that should be inlined, |
|
|
226 | for code size or speed reasons. |
|
|
227 | |
|
|
228 | Example: inline this function, it surely will reduce codesize. |
|
|
229 | |
|
|
230 | ecb_inline int |
|
|
231 | negmul (int a, int b) |
|
|
232 | { |
|
|
233 | return - (a * b); |
|
|
234 | } |
|
|
235 | |
106 | =item ecb_noinline |
236 | =item ecb_noinline |
107 | |
237 | |
108 | Prevent a function from being inlined - it might be optimised away, but |
238 | Prevent a function from being inlined - it might be optimised away, but |
109 | not inlined into other functions. This is useful if you know your function |
239 | not inlined into other functions. This is useful if you know your function |
110 | is rarely called and large enough for inlining not to be helpful. |
240 | is rarely called and large enough for inlining not to be helpful. |
… | |
… | |
123 | } |
253 | } |
124 | |
254 | |
125 | In this case, the compiler would probably be smart enough to deduce it on |
255 | In this case, the compiler would probably be smart enough to deduce it on |
126 | its own, so this is mainly useful for declarations. |
256 | its own, so this is mainly useful for declarations. |
127 | |
257 | |
|
|
258 | =item ecb_restrict |
|
|
259 | |
|
|
260 | Expands to the C<restrict> keyword or equivalent on compilers that support |
|
|
261 | them, and to nothing on others. Must be specified on a pointer type or |
|
|
262 | an array index to indicate that the memory doesn't alias with any other |
|
|
263 | restricted pointer in the same scope. |
|
|
264 | |
|
|
265 | Example: multiply a vector, and allow the compiler to parallelise the |
|
|
266 | loop, because it knows it doesn't overwrite input values. |
|
|
267 | |
|
|
268 | void |
|
|
269 | multiply (float *ecb_restrict src, |
|
|
270 | float *ecb_restrict dst, |
|
|
271 | int len, float factor) |
|
|
272 | { |
|
|
273 | int i; |
|
|
274 | |
|
|
275 | for (i = 0; i < len; ++i) |
|
|
276 | dst [i] = src [i] * factor; |
|
|
277 | } |
|
|
278 | |
128 | =item ecb_const |
279 | =item ecb_const |
129 | |
280 | |
130 | Declares that the function only depends on the values of its arguments, |
281 | Declares that the function only depends on the values of its arguments, |
131 | much like a mathematical function. It specifically does not read or write |
282 | much like a mathematical function. It specifically does not read or write |
132 | any memory any arguments might point to, global variables, or call any |
283 | any memory any arguments might point to, global variables, or call any |
… | |
… | |
192 | functions only called in exceptional or rare cases. |
343 | functions only called in exceptional or rare cases. |
193 | |
344 | |
194 | =item ecb_artificial |
345 | =item ecb_artificial |
195 | |
346 | |
196 | Declares the function as "artificial", in this case meaning that this |
347 | Declares the function as "artificial", in this case meaning that this |
197 | function is not really mean to be a function, but more like an accessor |
348 | function is not really meant to be a function, but more like an accessor |
198 | - many methods in C++ classes are mere accessor functions, and having a |
349 | - many methods in C++ classes are mere accessor functions, and having a |
199 | crash reported in such a method, or single-stepping through them, is not |
350 | crash reported in such a method, or single-stepping through them, is not |
200 | usually so helpful, especially when it's inlined to just a few instructions. |
351 | usually so helpful, especially when it's inlined to just a few instructions. |
201 | |
352 | |
202 | Marking them as artificial will instruct the debugger about just this, |
353 | Marking them as artificial will instruct the debugger about just this, |
… | |
… | |
222 | |
373 | |
223 | =head2 OPTIMISATION HINTS |
374 | =head2 OPTIMISATION HINTS |
224 | |
375 | |
225 | =over 4 |
376 | =over 4 |
226 | |
377 | |
227 | =item bool ecb_is_constant(expr) |
378 | =item bool ecb_is_constant (expr) |
228 | |
379 | |
229 | Returns true iff the expression can be deduced to be a compile-time |
380 | Returns true iff the expression can be deduced to be a compile-time |
230 | constant, and false otherwise. |
381 | constant, and false otherwise. |
231 | |
382 | |
232 | For example, when you have a C<rndm16> function that returns a 16 bit |
383 | For example, when you have a C<rndm16> function that returns a 16 bit |
… | |
… | |
381 | After processing the node, (part of) the next node might already be in |
532 | After processing the node, (part of) the next node might already be in |
382 | cache. |
533 | cache. |
383 | |
534 | |
384 | =back |
535 | =back |
385 | |
536 | |
386 | =head2 BIT FIDDLING / BITSTUFFS |
537 | =head2 BIT FIDDLING / BIT WIZARDRY |
387 | |
538 | |
388 | =over 4 |
539 | =over 4 |
389 | |
540 | |
390 | =item bool ecb_big_endian () |
541 | =item bool ecb_big_endian () |
391 | |
542 | |
… | |
… | |
397 | |
548 | |
398 | On systems that are neither, their return values are unspecified. |
549 | On systems that are neither, their return values are unspecified. |
399 | |
550 | |
400 | =item int ecb_ctz32 (uint32_t x) |
551 | =item int ecb_ctz32 (uint32_t x) |
401 | |
552 | |
|
|
553 | =item int ecb_ctz64 (uint64_t x) |
|
|
554 | |
402 | Returns the index of the least significant bit set in C<x> (or |
555 | Returns the index of the least significant bit set in C<x> (or |
403 | equivalently the number of bits set to 0 before the least significant bit |
556 | equivalently the number of bits set to 0 before the least significant bit |
404 | set), starting from 0. If C<x> is 0 the result is undefined. A common use |
557 | set), starting from 0. If C<x> is 0 the result is undefined. |
405 | case is to compute the integer binary logarithm, i.e., C<floor (log2 |
558 | |
|
|
559 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
|
|
560 | |
406 | (n))>. For example: |
561 | For example: |
407 | |
562 | |
408 | ecb_ctz32 (3) = 0 |
563 | ecb_ctz32 (3) = 0 |
409 | ecb_ctz32 (6) = 1 |
564 | ecb_ctz32 (6) = 1 |
410 | |
565 | |
|
|
566 | =item bool ecb_is_pot32 (uint32_t x) |
|
|
567 | |
|
|
568 | =item bool ecb_is_pot64 (uint32_t x) |
|
|
569 | |
|
|
570 | Return true iff C<x> is a power of two or C<x == 0>. |
|
|
571 | |
|
|
572 | For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. |
|
|
573 | |
|
|
574 | =item int ecb_ld32 (uint32_t x) |
|
|
575 | |
|
|
576 | =item int ecb_ld64 (uint64_t x) |
|
|
577 | |
|
|
578 | Returns the index of the most significant bit set in C<x>, or the number |
|
|
579 | of digits the number requires in binary (so that C<< 2**ld <= x < |
|
|
580 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
|
|
581 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
|
|
582 | example to see how many bits a certain number requires to be encoded. |
|
|
583 | |
|
|
584 | This function is similar to the "count leading zero bits" function, except |
|
|
585 | that that one returns how many zero bits are "in front" of the number (in |
|
|
586 | the given data type), while C<ecb_ld> returns how many bits the number |
|
|
587 | itself requires. |
|
|
588 | |
|
|
589 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
|
|
590 | |
411 | =item int ecb_popcount32 (uint32_t x) |
591 | =item int ecb_popcount32 (uint32_t x) |
412 | |
592 | |
|
|
593 | =item int ecb_popcount64 (uint64_t x) |
|
|
594 | |
413 | Returns the number of bits set to 1 in C<x>. For example: |
595 | Returns the number of bits set to 1 in C<x>. |
|
|
596 | |
|
|
597 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
|
|
598 | |
|
|
599 | For example: |
414 | |
600 | |
415 | ecb_popcount32 (7) = 3 |
601 | ecb_popcount32 (7) = 3 |
416 | ecb_popcount32 (255) = 8 |
602 | ecb_popcount32 (255) = 8 |
417 | |
603 | |
|
|
604 | =item uint8_t ecb_bitrev8 (uint8_t x) |
|
|
605 | |
|
|
606 | =item uint16_t ecb_bitrev16 (uint16_t x) |
|
|
607 | |
|
|
608 | =item uint32_t ecb_bitrev32 (uint32_t x) |
|
|
609 | |
|
|
610 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
|
|
611 | and so on. |
|
|
612 | |
|
|
613 | Example: |
|
|
614 | |
|
|
615 | ecb_bitrev8 (0xa7) = 0xea |
|
|
616 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
|
|
617 | |
418 | =item uint32_t ecb_bswap16 (uint32_t x) |
618 | =item uint32_t ecb_bswap16 (uint32_t x) |
419 | |
619 | |
420 | =item uint32_t ecb_bswap32 (uint32_t x) |
620 | =item uint32_t ecb_bswap32 (uint32_t x) |
421 | |
621 | |
|
|
622 | =item uint64_t ecb_bswap64 (uint64_t x) |
|
|
623 | |
422 | These two functions return the value of the 16-bit (32-bit) value C<x> |
624 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
423 | after reversing the order of bytes (0x11223344 becomes 0x44332211). |
625 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
|
|
626 | C<ecb_bswap32>). |
|
|
627 | |
|
|
628 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
|
|
629 | |
|
|
630 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
|
|
631 | |
|
|
632 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
|
|
633 | |
|
|
634 | =item uint64_t ecb_rotl64 (uint64_t x, unsigned int count) |
|
|
635 | |
|
|
636 | =item uint8_t ecb_rotr8 (uint8_t x, unsigned int count) |
|
|
637 | |
|
|
638 | =item uint16_t ecb_rotr16 (uint16_t x, unsigned int count) |
424 | |
639 | |
425 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
640 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
426 | |
641 | |
427 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
642 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
428 | |
643 | |
429 | These two functions return the value of C<x> after rotating all the bits |
644 | These two families of functions return the value of C<x> after rotating |
430 | by C<count> positions to the right or left respectively. |
645 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
|
|
646 | (C<ecb_rotl>). |
431 | |
647 | |
432 | Current GCC versions understand these functions and usually compile them |
648 | Current GCC versions understand these functions and usually compile them |
433 | to "optimal" code (e.g. a single C<roll> on x86). |
649 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
|
|
650 | x86). |
|
|
651 | |
|
|
652 | =back |
|
|
653 | |
|
|
654 | =head2 FLOATING POINT FIDDLING |
|
|
655 | |
|
|
656 | =over 4 |
|
|
657 | |
|
|
658 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
|
|
659 | |
|
|
660 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
|
|
661 | |
|
|
662 | These functions each take an argument in the native C<float> or C<double> |
|
|
663 | type and return the IEEE 754 bit representation of it. |
|
|
664 | |
|
|
665 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
|
|
666 | will be the most significant bit, followed by exponent and mantissa. |
|
|
667 | |
|
|
668 | This function should work even when the native floating point format isn't |
|
|
669 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
670 | also within reasonable limits (it tries to convert NaNs, infinities and |
|
|
671 | denormals, but will likely convert negative zero to positive zero). |
|
|
672 | |
|
|
673 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
674 | be able to optimise away this function completely. |
|
|
675 | |
|
|
676 | These functions can be helpful when serialising floats to the network - you |
|
|
677 | can serialise the return value like a normal uint32_t/uint64_t. |
|
|
678 | |
|
|
679 | Another use for these functions is to manipulate floating point values |
|
|
680 | directly. |
|
|
681 | |
|
|
682 | Silly example: toggle the sign bit of a float. |
|
|
683 | |
|
|
684 | /* On gcc-4.7 on amd64, */ |
|
|
685 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
|
|
686 | /* instructions to move the float value to an integer register and back. */ |
|
|
687 | |
|
|
688 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
|
|
689 | |
|
|
690 | =item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] |
|
|
691 | |
|
|
692 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
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693 | |
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694 | =item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] |
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695 | |
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696 | The reverse operation of the previos function - takes the bit |
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697 | representation of an IEEE binary16, binary32 or binary64 number and |
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698 | converts it to the native C<float> or C<double> format. |
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699 | |
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700 | This function should work even when the native floating point format isn't |
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701 | IEEE compliant, of course at a speed and code size penalty, and of course |
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702 | also within reasonable limits (it tries to convert normals and denormals, |
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703 | and might be lucky for infinities, and with extraordinary luck, also for |
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|
704 | negative zero). |
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705 | |
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706 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
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707 | be able to optimise away this function completely. |
434 | |
708 | |
435 | =back |
709 | =back |
436 | |
710 | |
437 | =head2 ARITHMETIC |
711 | =head2 ARITHMETIC |
438 | |
712 | |
… | |
… | |
448 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
722 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
449 | in the language. |
723 | in the language. |
450 | |
724 | |
451 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
725 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
452 | negatable, that is, both C<m> and C<-m> must be representable in its |
726 | negatable, that is, both C<m> and C<-m> must be representable in its |
453 | type (this typically includes the minimum signed integer value, the same |
727 | type (this typically excludes the minimum signed integer value, the same |
454 | limitation as for C</> and C<%> in C). |
728 | limitation as for C</> and C<%> in C). |
455 | |
729 | |
456 | Current GCC versions compile this into an efficient branchless sequence on |
730 | Current GCC versions compile this into an efficient branchless sequence on |
457 | many systems. |
731 | almost all CPUs. |
458 | |
732 | |
459 | For example, when you want to rotate forward through the members of an |
733 | For example, when you want to rotate forward through the members of an |
460 | array for increasing C<m> (which might be negative), then you should use |
734 | array for increasing C<m> (which might be negative), then you should use |
461 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
735 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
462 | change direction for negative values: |
736 | change direction for negative values: |
463 | |
737 | |
464 | for (m = -100; m <= 100; ++m) |
738 | for (m = -100; m <= 100; ++m) |
465 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
739 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
466 | |
740 | |
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741 | =item x = ecb_div_rd (val, div) |
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742 | |
|
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743 | =item x = ecb_div_ru (val, div) |
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744 | |
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745 | Returns C<val> divided by C<div> rounded down or up, respectively. |
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746 | C<val> and C<div> must have integer types and C<div> must be strictly |
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|
747 | positive. Note that these functions are implemented with macros in C |
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|
748 | and with function templates in C++. |
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|
749 | |
467 | =back |
750 | =back |
468 | |
751 | |
469 | =head2 UTILITY |
752 | =head2 UTILITY |
470 | |
753 | |
471 | =over 4 |
754 | =over 4 |
… | |
… | |
480 | for (i = 0; i < ecb_array_length (primes); i++) |
763 | for (i = 0; i < ecb_array_length (primes); i++) |
481 | sum += primes [i]; |
764 | sum += primes [i]; |
482 | |
765 | |
483 | =back |
766 | =back |
484 | |
767 | |
|
|
768 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
485 | |
769 | |
|
|
770 | These symbols need to be defined before including F<ecb.h> the first time. |
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771 | |
|
|
772 | =over 4 |
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773 | |
|
|
774 | =item ECB_NO_THREADS |
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775 | |
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|
776 | If F<ecb.h> is never used from multiple threads, then this symbol can |
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|
777 | be defined, in which case memory fences (and similar constructs) are |
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|
778 | completely removed, leading to more efficient code and fewer dependencies. |
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779 | |
|
|
780 | Setting this symbol to a true value implies C<ECB_NO_SMP>. |
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781 | |
|
|
782 | =item ECB_NO_SMP |
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783 | |
|
|
784 | The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from |
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|
785 | multiple threads, but never concurrently (e.g. if the system the program |
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|
786 | runs on has only a single CPU with a single core, no hyperthreading and so |
|
|
787 | on), then this symbol can be defined, leading to more efficient code and |
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|
788 | fewer dependencies. |
|
|
789 | |
|
|
790 | =item ECB_NO_LIBM |
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|
791 | |
|
|
792 | When defined to C<1>, do not export any functions that might introduce |
|
|
793 | dependencies on the math library (usually called F<-lm>) - these are |
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|
794 | marked with [-UECB_NO_LIBM]. |
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795 | |
|
|
796 | =back |
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797 | |
|
|
798 | |