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Revision 1.30 by root, Sat Jun 11 17:30:32 2011 UTC vs.
Revision 1.38 by sf-exg, Thu Aug 25 16:06:08 2011 UTC

… …
101 #else 101 #else
102 return 0; 102 return 0;
103 #endif 103 #endif
104 } 104 }
105 105
106=item ECB_INLINE 106=item ecb_inline
107 107
108This is not actually an attribute, but you use it like one. It expands 108This is not actually an attribute, but you use it like one. It expands
109either to C<static inline> or to just C<static>, if inline isn't 109either to C<static inline> or to just C<static>, if inline isn't
110supported. It should be used to declare functions that should be inlined, 110supported. It should be used to declare functions that should be inlined,
111for code size or speed reasons. 111for code size or speed reasons.
112 112
113Example: inline this function, it surely will reduce codesize. 113Example: inline this function, it surely will reduce codesize.
114 114
115 ECB_INLINE int 115 ecb_inline int
116 negmul (int a, int b) 116 negmul (int a, int b)
117 { 117 {
118 return - (a * b); 118 return - (a * b);
119 } 119 }
120 120
… …
396After processing the node, (part of) the next node might already be in 396After processing the node, (part of) the next node might already be in
397cache. 397cache.
398 398
399=back 399=back
400 400
401=head2 BIT FIDDLING / BITSTUFFS 401=head2 BIT FIDDLING / BIT WIZARDRY
402 402
403=over 4 403=over 4
404 404
405=item bool ecb_big_endian () 405=item bool ecb_big_endian ()
406 406
… …
412 412
413On systems that are neither, their return values are unspecified. 413On systems that are neither, their return values are unspecified.
414 414
415=item int ecb_ctz32 (uint32_t x) 415=item int ecb_ctz32 (uint32_t x)
416 416
417=item int ecb_ctz64 (uint64_t x)
418
417Returns the index of the least significant bit set in C<x> (or 419Returns the index of the least significant bit set in C<x> (or
418equivalently the number of bits set to 0 before the least significant bit 420equivalently the number of bits set to 0 before the least significant bit
419set), starting from 0. If C<x> is 0 the result is undefined. A common use 421set), starting from 0. If C<x> is 0 the result is undefined.
420case is to compute the integer binary logarithm, i.e., C<floor (log2 422
423For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
424
421(n))>. For example: 425For example:
422 426
423 ecb_ctz32 (3) = 0 427 ecb_ctz32 (3) = 0
424 ecb_ctz32 (6) = 1 428 ecb_ctz32 (6) = 1
425 429
430=item int ecb_ld32 (uint32_t x)
431
432=item int ecb_ld64 (uint64_t x)
433
434Returns the index of the most significant bit set in C<x>, or the number
435of digits the number requires in binary (so that C<< 2**ld <= x <
4362**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
437to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
438example to see how many bits a certain number requires to be encoded.
439
440This function is similar to the "count leading zero bits" function, except
441that that one returns how many zero bits are "in front" of the number (in
442the given data type), while C<ecb_ld> returns how many bits the number
443itself requires.
444
445For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
446
426=item int ecb_popcount32 (uint32_t x) 447=item int ecb_popcount32 (uint32_t x)
427 448
449=item int ecb_popcount64 (uint64_t x)
450
428Returns the number of bits set to 1 in C<x>. For example: 451Returns the number of bits set to 1 in C<x>.
452
453For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
454
455For example:
429 456
430 ecb_popcount32 (7) = 3 457 ecb_popcount32 (7) = 3
431 ecb_popcount32 (255) = 8 458 ecb_popcount32 (255) = 8
432 459
433=item uint32_t ecb_bswap16 (uint32_t x) 460=item uint32_t ecb_bswap16 (uint32_t x)
434 461
435=item uint32_t ecb_bswap32 (uint32_t x) 462=item uint32_t ecb_bswap32 (uint32_t x)
436 463
464=item uint64_t ecb_bswap64 (uint64_t x)
465
437These two functions return the value of the 16-bit (32-bit) value C<x> 466These functions return the value of the 16-bit (32-bit, 64-bit) value
438after reversing the order of bytes (0x11223344 becomes 0x44332211). 467C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
468C<ecb_bswap32>).
469
470=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
471
472=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
473
474=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
475
476=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
477
478=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
479
480=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
439 481
440=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) 482=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
441 483
442=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 484=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
443 485
444These two functions return the value of C<x> after rotating all the bits 486These two families of functions return the value of C<x> after rotating
445by C<count> positions to the right or left respectively. 487all the bits by C<count> positions to the right (C<ecb_rotr>) or left
488(C<ecb_rotl>).
446 489
447Current GCC versions understand these functions and usually compile them 490Current GCC versions understand these functions and usually compile them
448to "optimal" code (e.g. a single C<roll> on x86). 491to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
492x86).
449 493
450=back 494=back
451 495
452=head2 ARITHMETIC 496=head2 ARITHMETIC
453 497
… …
477change direction for negative values: 521change direction for negative values:
478 522
479 for (m = -100; m <= 100; ++m) 523 for (m = -100; m <= 100; ++m)
480 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; 524 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
481 525
526=item x = ecb_div_rd (val, div)
527
528=item x = ecb_div_ru (val, div)
529
530Returns C<val> divided by C<div> rounded down or up, respectively.
531C<val> and C<div> must have integer types and C<div> must be strictly
532positive. Note that these functions are implemented with macros in C
533and with function templates in C++.
534
482=back 535=back
483 536
484=head2 UTILITY 537=head2 UTILITY
485 538
486=over 4 539=over 4

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