… | |
… | |
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 |
|
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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 | while not claiming to be C++. |
|
|
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, while not claiming to be C++. |
|
|
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, while not claiming to be C++. |
|
|
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 | =item ECB_AMD64, ECB_AMD64_X32 |
|
|
156 | |
|
|
157 | These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
|
|
158 | ABI, respectively, and undefined elsewhere. |
|
|
159 | |
|
|
160 | The designers of the new X32 ABI for some inexplicable reason decided to |
|
|
161 | make it look exactly like amd64, even though it's completely incompatible |
|
|
162 | to that ABI, breaking about every piece of software that assumed that |
|
|
163 | C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
|
|
164 | necessary. |
|
|
165 | |
|
|
166 | =back |
58 | |
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 |
… | |
… | |
101 | #else |
210 | #else |
102 | return 0; |
211 | return 0; |
103 | #endif |
212 | #endif |
104 | } |
213 | } |
105 | |
214 | |
|
|
215 | =item ecb_deprecated |
|
|
216 | |
|
|
217 | Similar to C<ecb_unused>, but marks a function, variable or type as |
|
|
218 | deprecated. This makes some compilers warn when the type is used. |
|
|
219 | |
106 | =item ecb_inline |
220 | =item ecb_inline |
107 | |
221 | |
108 | This is not actually an attribute, but you use it like one. It expands |
222 | This is not actually an attribute, but you use it like one. It expands |
109 | either to C<static inline> or to just C<static>, if inline isn't |
223 | either to C<static inline> or to just C<static>, if inline isn't |
110 | supported. It should be used to declare functions that should be inlined, |
224 | supported. It should be used to declare functions that should be inlined, |
… | |
… | |
138 | } |
252 | } |
139 | |
253 | |
140 | In this case, the compiler would probably be smart enough to deduce it on |
254 | In this case, the compiler would probably be smart enough to deduce it on |
141 | its own, so this is mainly useful for declarations. |
255 | its own, so this is mainly useful for declarations. |
142 | |
256 | |
|
|
257 | =item ecb_restrict |
|
|
258 | |
|
|
259 | Expands to the C<restrict> keyword or equivalent on compilers that support |
|
|
260 | them, and to nothing on others. Must be specified on a pointer type or |
|
|
261 | an array index to indicate that the memory doesn't alias with any other |
|
|
262 | restricted pointer in the same scope. |
|
|
263 | |
|
|
264 | Example: multiply a vector, and allow the compiler to parallelise the |
|
|
265 | loop, because it knows it doesn't overwrite input values. |
|
|
266 | |
|
|
267 | void |
|
|
268 | multiply (float *ecb_restrict src, |
|
|
269 | float *ecb_restrict dst, |
|
|
270 | int len, float factor) |
|
|
271 | { |
|
|
272 | int i; |
|
|
273 | |
|
|
274 | for (i = 0; i < len; ++i) |
|
|
275 | dst [i] = src [i] * factor; |
|
|
276 | } |
|
|
277 | |
143 | =item ecb_const |
278 | =item ecb_const |
144 | |
279 | |
145 | Declares that the function only depends on the values of its arguments, |
280 | 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 |
281 | 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 |
282 | any memory any arguments might point to, global variables, or call any |
… | |
… | |
207 | functions only called in exceptional or rare cases. |
342 | functions only called in exceptional or rare cases. |
208 | |
343 | |
209 | =item ecb_artificial |
344 | =item ecb_artificial |
210 | |
345 | |
211 | Declares the function as "artificial", in this case meaning that this |
346 | 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 |
347 | 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 |
348 | - 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 |
349 | 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. |
350 | usually so helpful, especially when it's inlined to just a few instructions. |
216 | |
351 | |
217 | Marking them as artificial will instruct the debugger about just this, |
352 | Marking them as artificial will instruct the debugger about just this, |
… | |
… | |
396 | After processing the node, (part of) the next node might already be in |
531 | After processing the node, (part of) the next node might already be in |
397 | cache. |
532 | cache. |
398 | |
533 | |
399 | =back |
534 | =back |
400 | |
535 | |
401 | =head2 BIT FIDDLING / BITSTUFFS |
536 | =head2 BIT FIDDLING / BIT WIZARDRY |
402 | |
537 | |
403 | =over 4 |
538 | =over 4 |
404 | |
539 | |
405 | =item bool ecb_big_endian () |
540 | =item bool ecb_big_endian () |
406 | |
541 | |
… | |
… | |
412 | |
547 | |
413 | On systems that are neither, their return values are unspecified. |
548 | On systems that are neither, their return values are unspecified. |
414 | |
549 | |
415 | =item int ecb_ctz32 (uint32_t x) |
550 | =item int ecb_ctz32 (uint32_t x) |
416 | |
551 | |
|
|
552 | =item int ecb_ctz64 (uint64_t x) |
|
|
553 | |
417 | Returns the index of the least significant bit set in C<x> (or |
554 | Returns the index of the least significant bit set in C<x> (or |
418 | equivalently the number of bits set to 0 before the least significant bit |
555 | equivalently the number of bits set to 0 before the least significant bit |
419 | set), starting from 0. If C<x> is 0 the result is undefined. For example: |
556 | set), starting from 0. If C<x> is 0 the result is undefined. |
|
|
557 | |
|
|
558 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
|
|
559 | |
|
|
560 | For example: |
420 | |
561 | |
421 | ecb_ctz32 (3) = 0 |
562 | ecb_ctz32 (3) = 0 |
422 | ecb_ctz32 (6) = 1 |
563 | ecb_ctz32 (6) = 1 |
423 | |
564 | |
|
|
565 | =item bool ecb_is_pot32 (uint32_t x) |
|
|
566 | |
|
|
567 | =item bool ecb_is_pot64 (uint32_t x) |
|
|
568 | |
|
|
569 | Return true iff C<x> is a power of two or C<x == 0>. |
|
|
570 | |
|
|
571 | For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>. |
|
|
572 | |
|
|
573 | =item int ecb_ld32 (uint32_t x) |
|
|
574 | |
|
|
575 | =item int ecb_ld64 (uint64_t x) |
|
|
576 | |
|
|
577 | Returns the index of the most significant bit set in C<x>, or the number |
|
|
578 | of digits the number requires in binary (so that C<< 2**ld <= x < |
|
|
579 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
|
|
580 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
|
|
581 | example to see how many bits a certain number requires to be encoded. |
|
|
582 | |
|
|
583 | This function is similar to the "count leading zero bits" function, except |
|
|
584 | that that one returns how many zero bits are "in front" of the number (in |
|
|
585 | the given data type), while C<ecb_ld> returns how many bits the number |
|
|
586 | itself requires. |
|
|
587 | |
|
|
588 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
|
|
589 | |
424 | =item int ecb_popcount32 (uint32_t x) |
590 | =item int ecb_popcount32 (uint32_t x) |
425 | |
591 | |
|
|
592 | =item int ecb_popcount64 (uint64_t x) |
|
|
593 | |
426 | Returns the number of bits set to 1 in C<x>. For example: |
594 | Returns the number of bits set to 1 in C<x>. |
|
|
595 | |
|
|
596 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
|
|
597 | |
|
|
598 | For example: |
427 | |
599 | |
428 | ecb_popcount32 (7) = 3 |
600 | ecb_popcount32 (7) = 3 |
429 | ecb_popcount32 (255) = 8 |
601 | ecb_popcount32 (255) = 8 |
430 | |
602 | |
|
|
603 | =item uint8_t ecb_bitrev8 (uint8_t x) |
|
|
604 | |
|
|
605 | =item uint16_t ecb_bitrev16 (uint16_t x) |
|
|
606 | |
|
|
607 | =item uint32_t ecb_bitrev32 (uint32_t x) |
|
|
608 | |
|
|
609 | Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
|
|
610 | and so on. |
|
|
611 | |
|
|
612 | Example: |
|
|
613 | |
|
|
614 | ecb_bitrev8 (0xa7) = 0xea |
|
|
615 | ecb_bitrev32 (0xffcc4411) = 0x882233ff |
|
|
616 | |
431 | =item uint32_t ecb_bswap16 (uint32_t x) |
617 | =item uint32_t ecb_bswap16 (uint32_t x) |
432 | |
618 | |
433 | =item uint32_t ecb_bswap32 (uint32_t x) |
619 | =item uint32_t ecb_bswap32 (uint32_t x) |
434 | |
620 | |
|
|
621 | =item uint64_t ecb_bswap64 (uint64_t x) |
|
|
622 | |
435 | These two functions return the value of the 16-bit (32-bit) value C<x> |
623 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
436 | after reversing the order of bytes (0x11223344 becomes 0x44332211). |
624 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
|
|
625 | C<ecb_bswap32>). |
|
|
626 | |
|
|
627 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
|
|
628 | |
|
|
629 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
|
|
630 | |
|
|
631 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
|
|
632 | |
|
|
633 | =item uint64_t ecb_rotl64 (uint64_t x, unsigned int count) |
|
|
634 | |
|
|
635 | =item uint8_t ecb_rotr8 (uint8_t x, unsigned int count) |
|
|
636 | |
|
|
637 | =item uint16_t ecb_rotr16 (uint16_t x, unsigned int count) |
437 | |
638 | |
438 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
639 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
439 | |
640 | |
440 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
641 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
441 | |
642 | |
442 | These two functions return the value of C<x> after rotating all the bits |
643 | These two families of functions return the value of C<x> after rotating |
443 | by C<count> positions to the right or left respectively. |
644 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
|
|
645 | (C<ecb_rotl>). |
444 | |
646 | |
445 | Current GCC versions understand these functions and usually compile them |
647 | Current GCC versions understand these functions and usually compile them |
446 | to "optimal" code (e.g. a single C<roll> on x86). |
648 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
|
|
649 | x86). |
|
|
650 | |
|
|
651 | =back |
|
|
652 | |
|
|
653 | =head2 FLOATING POINT FIDDLING |
|
|
654 | |
|
|
655 | =over 4 |
|
|
656 | |
|
|
657 | =item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
|
|
658 | |
|
|
659 | =item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
|
|
660 | |
|
|
661 | These functions each take an argument in the native C<float> or C<double> |
|
|
662 | type and return the IEEE 754 bit representation of it. |
|
|
663 | |
|
|
664 | The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
|
|
665 | will be the most significant bit, followed by exponent and mantissa. |
|
|
666 | |
|
|
667 | This function should work even when the native floating point format isn't |
|
|
668 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
669 | also within reasonable limits (it tries to convert NaNs, infinities and |
|
|
670 | denormals, but will likely convert negative zero to positive zero). |
|
|
671 | |
|
|
672 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
673 | be able to optimise away this function completely. |
|
|
674 | |
|
|
675 | These functions can be helpful when serialising floats to the network - you |
|
|
676 | can serialise the return value like a normal uint32_t/uint64_t. |
|
|
677 | |
|
|
678 | Another use for these functions is to manipulate floating point values |
|
|
679 | directly. |
|
|
680 | |
|
|
681 | Silly example: toggle the sign bit of a float. |
|
|
682 | |
|
|
683 | /* On gcc-4.7 on amd64, */ |
|
|
684 | /* this results in a single add instruction to toggle the bit, and 4 extra */ |
|
|
685 | /* instructions to move the float value to an integer register and back. */ |
|
|
686 | |
|
|
687 | x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
|
|
688 | |
|
|
689 | =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
|
|
690 | |
|
|
691 | =item double ecb_binary32_to_double (uint64_t x) [-UECB_NO_LIBM] |
|
|
692 | |
|
|
693 | The reverse operation of the previos function - takes the bit representation |
|
|
694 | of an IEEE binary32 or binary64 number and converts it to the native C<float> |
|
|
695 | or C<double> format. |
|
|
696 | |
|
|
697 | This function should work even when the native floating point format isn't |
|
|
698 | IEEE compliant, of course at a speed and code size penalty, and of course |
|
|
699 | also within reasonable limits (it tries to convert normals and denormals, |
|
|
700 | and might be lucky for infinities, and with extraordinary luck, also for |
|
|
701 | negative zero). |
|
|
702 | |
|
|
703 | On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
|
|
704 | be able to optimise away this function completely. |
447 | |
705 | |
448 | =back |
706 | =back |
449 | |
707 | |
450 | =head2 ARITHMETIC |
708 | =head2 ARITHMETIC |
451 | |
709 | |
… | |
… | |
475 | change direction for negative values: |
733 | change direction for negative values: |
476 | |
734 | |
477 | for (m = -100; m <= 100; ++m) |
735 | for (m = -100; m <= 100; ++m) |
478 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
736 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
479 | |
737 | |
|
|
738 | =item x = ecb_div_rd (val, div) |
|
|
739 | |
|
|
740 | =item x = ecb_div_ru (val, div) |
|
|
741 | |
|
|
742 | Returns C<val> divided by C<div> rounded down or up, respectively. |
|
|
743 | C<val> and C<div> must have integer types and C<div> must be strictly |
|
|
744 | positive. Note that these functions are implemented with macros in C |
|
|
745 | and with function templates in C++. |
|
|
746 | |
480 | =back |
747 | =back |
481 | |
748 | |
482 | =head2 UTILITY |
749 | =head2 UTILITY |
483 | |
750 | |
484 | =over 4 |
751 | =over 4 |
… | |
… | |
493 | for (i = 0; i < ecb_array_length (primes); i++) |
760 | for (i = 0; i < ecb_array_length (primes); i++) |
494 | sum += primes [i]; |
761 | sum += primes [i]; |
495 | |
762 | |
496 | =back |
763 | =back |
497 | |
764 | |
|
|
765 | =head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
498 | |
766 | |
|
|
767 | These symbols need to be defined before including F<ecb.h> the first time. |
|
|
768 | |
|
|
769 | =over 4 |
|
|
770 | |
|
|
771 | =item ECB_NO_THREADS |
|
|
772 | |
|
|
773 | If F<ecb.h> is never used from multiple threads, then this symbol can |
|
|
774 | be defined, in which case memory fences (and similar constructs) are |
|
|
775 | completely removed, leading to more efficient code and fewer dependencies. |
|
|
776 | |
|
|
777 | Setting this symbol to a true value implies C<ECB_NO_SMP>. |
|
|
778 | |
|
|
779 | =item ECB_NO_SMP |
|
|
780 | |
|
|
781 | The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from |
|
|
782 | multiple threads, but never concurrently (e.g. if the system the program |
|
|
783 | runs on has only a single CPU with a single core, no hyperthreading and so |
|
|
784 | on), then this symbol can be defined, leading to more efficient code and |
|
|
785 | fewer dependencies. |
|
|
786 | |
|
|
787 | =item ECB_NO_LIBM |
|
|
788 | |
|
|
789 | When defined to C<1>, do not export any functions that might introduce |
|
|
790 | dependencies on the math library (usually called F<-lm>) - these are |
|
|
791 | marked with [-UECB_NO_LIBM]. |
|
|
792 | |
|
|
793 | =back |
|
|
794 | |
|
|
795 | |