… | |
… | |
53 | C<uint32_t>, then the corresponding function works only with that type. If |
53 | C<uint32_t>, then the corresponding function works only with that type. If |
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 | |
|
|
59 | =head2 TYPES / TYPE SUPPORT |
|
|
60 | |
|
|
61 | ecb.h makes sure that the following types are defined (in the expected way): |
|
|
62 | |
|
|
63 | int8_t uint8_t int16_t uint16_t |
|
|
64 | int32_t uint32_t int64_t uint64_t |
|
|
65 | intptr_t uintptr_t |
|
|
66 | |
|
|
67 | 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 |
|
|
69 | expressions. |
|
|
70 | |
|
|
71 | For C<ptrdiff_t> and C<size_t> use C<stddef.h>. |
|
|
72 | |
|
|
73 | =head2 LANGUAGE/COMPILER VERSIONS |
|
|
74 | |
|
|
75 | 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 |
|
|
77 | ensure it's either C<0> or C<1> if you need that). |
|
|
78 | |
|
|
79 | =over 4 |
|
|
80 | |
|
|
81 | =item ECB_C |
|
|
82 | |
|
|
83 | True if the implementation defines the C<__STDC__> macro to a true value, |
|
|
84 | which is typically true for both C and C++ compilers. |
|
|
85 | |
|
|
86 | =item ECB_C99 |
|
|
87 | |
|
|
88 | True if the implementation claims to be compliant to C99 (ISO/IEC |
|
|
89 | 9899:1999) or any later version. |
|
|
90 | |
|
|
91 | Note that later versions (ECB_C11) remove core features again (for |
|
|
92 | example, variable length arrays). |
|
|
93 | |
|
|
94 | =item ECB_C11 |
|
|
95 | |
|
|
96 | True if the implementation claims to be compliant to C11 (ISO/IEC |
|
|
97 | 9899:2011) or any later version. |
|
|
98 | |
|
|
99 | =item ECB_CPP |
|
|
100 | |
|
|
101 | True if the implementation defines the C<__cplusplus__> macro to a true |
|
|
102 | value, which is typically true for C++ compilers. |
|
|
103 | |
|
|
104 | =item ECB_CPP11 |
|
|
105 | |
|
|
106 | True if the implementation claims to be compliant to ISO/IEC 14882:2011 |
|
|
107 | (C++11) or any later version. |
|
|
108 | |
|
|
109 | =item ECB_GCC_VERSION(major,minor) |
|
|
110 | |
|
|
111 | Expands to a true value (suitable for testing in by the preprocessor) |
|
|
112 | if the compiler used is GNU C and the version is the given version, or |
|
|
113 | higher. |
|
|
114 | |
|
|
115 | This macro tries to return false on compilers that claim to be GCC |
|
|
116 | compatible but aren't. |
|
|
117 | |
|
|
118 | =item ECB_EXTERN_C |
|
|
119 | |
|
|
120 | Expands to C<extern "C"> in C++, and a simple C<extern> in C. |
|
|
121 | |
|
|
122 | This can be used to declare a single external C function: |
|
|
123 | |
|
|
124 | ECB_EXTERN_C int printf (const char *format, ...); |
|
|
125 | |
|
|
126 | =item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END |
|
|
127 | |
|
|
128 | These two macros can be used to wrap multiple C<extern "C"> definitions - |
|
|
129 | they expand to nothing in C. |
|
|
130 | |
|
|
131 | They are most useful in header files: |
|
|
132 | |
|
|
133 | ECB_EXTERN_C_BEG |
|
|
134 | |
|
|
135 | int mycfun1 (int x); |
|
|
136 | int mycfun2 (int x); |
|
|
137 | |
|
|
138 | ECB_EXTERN_C_END |
|
|
139 | |
|
|
140 | =item ECB_STDFP |
|
|
141 | |
|
|
142 | If this evaluates to a true value (suitable for testing in by the |
|
|
143 | preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
|
|
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>. |
|
|
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. |
|
|
150 | |
|
|
151 | 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 |
|
|
153 | side. |
|
|
154 | |
|
|
155 | =back |
58 | |
156 | |
59 | =head2 GCC ATTRIBUTES |
157 | =head2 GCC ATTRIBUTES |
60 | |
158 | |
61 | A major part of libecb deals with GCC attributes. These are additional |
159 | A major part of libecb deals with GCC attributes. These are additional |
62 | attributes that you can assign to functions, variables and sometimes even |
160 | attributes that you can assign to functions, variables and sometimes even |
… | |
… | |
138 | } |
236 | } |
139 | |
237 | |
140 | In this case, the compiler would probably be smart enough to deduce it on |
238 | In this case, the compiler would probably be smart enough to deduce it on |
141 | its own, so this is mainly useful for declarations. |
239 | its own, so this is mainly useful for declarations. |
142 | |
240 | |
|
|
241 | =item ecb_restrict |
|
|
242 | |
|
|
243 | Expands to the C<restrict> keyword or equivalent on compilers that support |
|
|
244 | them, and to nothing on others. Must be specified on a pointer type or |
|
|
245 | an array index to indicate that the memory doesn't alias with any other |
|
|
246 | restricted pointer in the same scope. |
|
|
247 | |
|
|
248 | Example: multiply a vector, and allow the compiler to parallelise the |
|
|
249 | loop, because it knows it doesn't overwrite input values. |
|
|
250 | |
|
|
251 | void |
|
|
252 | multiply (float *ecb_restrict src, |
|
|
253 | float *ecb_restrict dst, |
|
|
254 | int len, float factor) |
|
|
255 | { |
|
|
256 | int i; |
|
|
257 | |
|
|
258 | for (i = 0; i < len; ++i) |
|
|
259 | dst [i] = src [i] * factor; |
|
|
260 | } |
|
|
261 | |
143 | =item ecb_const |
262 | =item ecb_const |
144 | |
263 | |
145 | Declares that the function only depends on the values of its arguments, |
264 | Declares that the function only depends on the values of its arguments, |
146 | much like a mathematical function. It specifically does not read or write |
265 | much like a mathematical function. It specifically does not read or write |
147 | any memory any arguments might point to, global variables, or call any |
266 | any memory any arguments might point to, global variables, or call any |
… | |
… | |
207 | functions only called in exceptional or rare cases. |
326 | functions only called in exceptional or rare cases. |
208 | |
327 | |
209 | =item ecb_artificial |
328 | =item ecb_artificial |
210 | |
329 | |
211 | Declares the function as "artificial", in this case meaning that this |
330 | Declares the function as "artificial", in this case meaning that this |
212 | function is not really mean to be a function, but more like an accessor |
331 | function is not really meant to be a function, but more like an accessor |
213 | - many methods in C++ classes are mere accessor functions, and having a |
332 | - many methods in C++ classes are mere accessor functions, and having a |
214 | crash reported in such a method, or single-stepping through them, is not |
333 | crash reported in such a method, or single-stepping through them, is not |
215 | usually so helpful, especially when it's inlined to just a few instructions. |
334 | usually so helpful, especially when it's inlined to just a few instructions. |
216 | |
335 | |
217 | Marking them as artificial will instruct the debugger about just this, |
336 | Marking them as artificial will instruct the debugger about just this, |
… | |
… | |
425 | For example: |
544 | For example: |
426 | |
545 | |
427 | ecb_ctz32 (3) = 0 |
546 | ecb_ctz32 (3) = 0 |
428 | ecb_ctz32 (6) = 1 |
547 | ecb_ctz32 (6) = 1 |
429 | |
548 | |
|
|
549 | =item bool ecb_is_pot32 (uint32_t x) |
|
|
550 | |
|
|
551 | =item bool ecb_is_pot64 (uint32_t x) |
|
|
552 | |
|
|
553 | Return true iff C<x> is a power of two or C<x == 0>. |
|
|
554 | |
|
|
555 | For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. |
|
|
556 | |
430 | =item int ecb_ld32 (uint32_t x) |
557 | =item int ecb_ld32 (uint32_t x) |
431 | |
558 | |
432 | =item int ecb_ld64 (uint64_t x) |
559 | =item int ecb_ld64 (uint64_t x) |
433 | |
560 | |
434 | Returns the index of the most significant bit set in C<x>, or the number |
561 | Returns the index of the most significant bit set in C<x>, or the number |
… | |
… | |
455 | For example: |
582 | For example: |
456 | |
583 | |
457 | ecb_popcount32 (7) = 3 |
584 | ecb_popcount32 (7) = 3 |
458 | ecb_popcount32 (255) = 8 |
585 | ecb_popcount32 (255) = 8 |
459 | |
586 | |
|
|
587 | =item uint8_t ecb_bitrev8 (uint8_t x) |
|
|
588 | |
|
|
589 | =item uint16_t ecb_bitrev16 (uint16_t x) |
|
|
590 | |
|
|
591 | =item uint32_t ecb_bitrev32 (uint32_t x) |
|
|
592 | |
|
|
593 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
|
|
594 | and so on. |
|
|
595 | |
|
|
596 | Example: |
|
|
597 | |
|
|
598 | ecb_bitrev8 (0xa7) = 0xea |
|
|
599 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
|
|
600 | |
460 | =item uint32_t ecb_bswap16 (uint32_t x) |
601 | =item uint32_t ecb_bswap16 (uint32_t x) |
461 | |
602 | |
462 | =item uint32_t ecb_bswap32 (uint32_t x) |
603 | =item uint32_t ecb_bswap32 (uint32_t x) |
463 | |
604 | |
464 | =item uint64_t ecb_bswap64 (uint64_t x) |
605 | =item uint64_t ecb_bswap64 (uint64_t x) |
… | |
… | |
488 | (C<ecb_rotl>). |
629 | (C<ecb_rotl>). |
489 | |
630 | |
490 | Current GCC versions understand these functions and usually compile them |
631 | Current GCC versions understand these functions and usually compile them |
491 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
632 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
492 | x86). |
633 | x86). |
|
|
634 | |
|
|
635 | =back |
|
|
636 | |
|
|
637 | =head2 FLOATING POINT FIDDLING |
|
|
638 | |
|
|
639 | =over 4 |
|
|
640 | |
|
|
641 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
|
|
642 | |
|
|
643 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
|
|
644 | |
|
|
645 | These functions each take an argument in the native C<float> or C<double> |
|
|
646 | type and return the IEEE 754 bit representation of it. |
|
|
647 | |
|
|
648 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
|
|
649 | will be the most significant bit, followed by exponent and mantissa. |
|
|
650 | |
|
|
651 | This function should work even when the native floating point format isn't |
|
|
652 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
653 | also within reasonable limits (it tries to convert NaNs, infinities and |
|
|
654 | denormals, but will likely convert negative zero to positive zero). |
|
|
655 | |
|
|
656 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
657 | be able to optimise away this function completely. |
|
|
658 | |
|
|
659 | These functions can be helpful when serialising floats to the network - you |
|
|
660 | can serialise the return value like a normal uint32_t/uint64_t. |
|
|
661 | |
|
|
662 | Another use for these functions is to manipulate floating point values |
|
|
663 | directly. |
|
|
664 | |
|
|
665 | Silly example: toggle the sign bit of a float. |
|
|
666 | |
|
|
667 | /* On gcc-4.7 on amd64, */ |
|
|
668 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
|
|
669 | /* instructions to move the float value to an integer register and back. */ |
|
|
670 | |
|
|
671 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
|
|
672 | |
|
|
673 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
|
|
674 | |
|
|
675 | =item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] |
|
|
676 | |
|
|
677 | The reverse operation of the previos function - takes the bit representation |
|
|
678 | of an IEEE binary32 or binary64 number and converts it to the native C<float> |
|
|
679 | or C<double> format. |
|
|
680 | |
|
|
681 | This function should work even when the native floating point format isn't |
|
|
682 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
683 | also within reasonable limits (it tries to convert normals and denormals, |
|
|
684 | and might be lucky for infinities, and with extraordinary luck, also for |
|
|
685 | negative zero). |
|
|
686 | |
|
|
687 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
688 | be able to optimise away this function completely. |
493 | |
689 | |
494 | =back |
690 | =back |
495 | |
691 | |
496 | =head2 ARITHMETIC |
692 | =head2 ARITHMETIC |
497 | |
693 | |
… | |
… | |
548 | for (i = 0; i < ecb_array_length (primes); i++) |
744 | for (i = 0; i < ecb_array_length (primes); i++) |
549 | sum += primes [i]; |
745 | sum += primes [i]; |
550 | |
746 | |
551 | =back |
747 | =back |
552 | |
748 | |
|
|
749 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
553 | |
750 | |
|
|
751 | These symbols need to be defined before including F<ecb.h> the first time. |
|
|
752 | |
|
|
753 | =over 4 |
|
|
754 | |
|
|
755 | =item ECB_NO_THREADS |
|
|
756 | |
|
|
757 | If F<ecb.h> is never used from multiple threads, then this symbol can |
|
|
758 | be defined, in which case memory fences (and similar constructs) are |
|
|
759 | completely removed, leading to more efficient code and fewer dependencies. |
|
|
760 | |
|
|
761 | Setting this symbol to a true value implies C<ECB_NO_SMP>. |
|
|
762 | |
|
|
763 | =item ECB_NO_SMP |
|
|
764 | |
|
|
765 | The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from |
|
|
766 | multiple threads, but never concurrently (e.g. if the system the program |
|
|
767 | runs on has only a single CPU with a single core, no hyperthreading and so |
|
|
768 | on), then this symbol can be defined, leading to more efficient code and |
|
|
769 | fewer dependencies. |
|
|
770 | |
|
|
771 | =item ECB_NO_LIBM |
|
|
772 | |
|
|
773 | When defined to C<1>, do not export any functions that might introduce |
|
|
774 | dependencies on the math library (usually called F<-lm>) - these are |
|
|
775 | marked with [-UECB_NO_LIBM]. |
|
|
776 | |
|
|
777 | =back |
|
|
778 | |
|
|
779 | |