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Revision 1.33 by root, Fri Jun 17 18:46:19 2011 UTC vs.
Revision 1.41 by root, Mon May 28 08:40:25 2012 UTC

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53C<uint32_t>, then the corresponding function works only with that type. If 53C<uint32_t>, then the corresponding function works only with that type. If
54only a generic name is used (C<expr>, C<cond>, C<value> and so on), then 54only a generic name is used (C<expr>, C<cond>, C<value> and so on), then
55the corresponding function relies on C to implement the correct types, and 55the corresponding function relies on C to implement the correct types, and
56is usually implemented as a macro. Specifically, a "bool" in this manual 56is usually implemented as a macro. Specifically, a "bool" in this manual
57refers to any kind of boolean value, not a specific type. 57refers to any kind of boolean value, not a specific type.
58
59=head2 TYPES / TYPE SUPPORT
60
61ecb.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
67The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this
68platform (currently C<4> or C<8>).
58 69
59=head2 GCC ATTRIBUTES 70=head2 GCC ATTRIBUTES
60 71
61A major part of libecb deals with GCC attributes. These are additional 72A major part of libecb deals with GCC attributes. These are additional
62attributes that you can assign to functions, variables and sometimes even 73attributes that you can assign to functions, variables and sometimes even
… …
396After processing the node, (part of) the next node might already be in 407After processing the node, (part of) the next node might already be in
397cache. 408cache.
398 409
399=back 410=back
400 411
401=head2 BIT FIDDLING / BITSTUFFS 412=head2 BIT FIDDLING / BIT WIZARDRY
402 413
403=over 4 414=over 4
404 415
405=item bool ecb_big_endian () 416=item bool ecb_big_endian ()
406 417
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412 423
413On systems that are neither, their return values are unspecified. 424On systems that are neither, their return values are unspecified.
414 425
415=item int ecb_ctz32 (uint32_t x) 426=item int ecb_ctz32 (uint32_t x)
416 427
428=item int ecb_ctz64 (uint64_t x)
429
417Returns the index of the least significant bit set in C<x> (or 430Returns 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 431equivalently 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. For example: 432set), starting from 0. If C<x> is 0 the result is undefined.
433
434For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
435
436For example:
420 437
421 ecb_ctz32 (3) = 0 438 ecb_ctz32 (3) = 0
422 ecb_ctz32 (6) = 1 439 ecb_ctz32 (6) = 1
423 440
441=item bool ecb_is_pot32 (uint32_t x)
442
443=item bool ecb_is_pot64 (uint32_t x)
444
445Return true iff C<x> is a power of two or C<x == 0>.
446
447For smaller types then C<uint32_t> you can safely use C<ecb_is_pot32>.
448
449=item int ecb_ld32 (uint32_t x)
450
451=item int ecb_ld64 (uint64_t x)
452
453Returns the index of the most significant bit set in C<x>, or the number
454of digits the number requires in binary (so that C<< 2**ld <= x <
4552**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is
456to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for
457example to see how many bits a certain number requires to be encoded.
458
459This function is similar to the "count leading zero bits" function, except
460that that one returns how many zero bits are "in front" of the number (in
461the given data type), while C<ecb_ld> returns how many bits the number
462itself requires.
463
464For smaller types than C<uint32_t> you can safely use C<ecb_ld32>.
465
424=item int ecb_popcount32 (uint32_t x) 466=item int ecb_popcount32 (uint32_t x)
425 467
468=item int ecb_popcount64 (uint64_t x)
469
426Returns the number of bits set to 1 in C<x>. For example: 470Returns the number of bits set to 1 in C<x>.
471
472For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>.
473
474For example:
427 475
428 ecb_popcount32 (7) = 3 476 ecb_popcount32 (7) = 3
429 ecb_popcount32 (255) = 8 477 ecb_popcount32 (255) = 8
430 478
479=item uint8_t ecb_bitrev8 (uint8_t x)
480
481=item uint16_t ecb_bitrev16 (uint16_t x)
482
483=item uint32_t ecb_bitrev32 (uint32_t x)
484
485Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1
486and so on.
487
488Example:
489
490 ecb_bitrev8 (0xa7) = 0xea
491 ecb_bitrev32 (0xffcc4411) = 0x882233ff
492
431=item uint32_t ecb_bswap16 (uint32_t x) 493=item uint32_t ecb_bswap16 (uint32_t x)
432 494
433=item uint32_t ecb_bswap32 (uint32_t x) 495=item uint32_t ecb_bswap32 (uint32_t x)
434 496
497=item uint64_t ecb_bswap64 (uint64_t x)
498
435These two functions return the value of the 16-bit (32-bit) value C<x> 499These functions return the value of the 16-bit (32-bit, 64-bit) value
436after reversing the order of bytes (0x11223344 becomes 0x44332211). 500C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in
501C<ecb_bswap32>).
502
503=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count)
504
505=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count)
506
507=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
508
509=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
510
511=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count)
512
513=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count)
437 514
438=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) 515=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
439 516
440=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count)
441
442=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) 517=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
443 518
444=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count)
445
446These two functions return the value of C<x> after rotating all the bits 519These two families of functions return the value of C<x> after rotating
447by C<count> positions to the right or left respectively. 520all the bits by C<count> positions to the right (C<ecb_rotr>) or left
521(C<ecb_rotl>).
448 522
449Current GCC versions understand these functions and usually compile them 523Current GCC versions understand these functions and usually compile them
450to "optimal" code (e.g. a single C<roll> on x86). 524to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on
525x86).
451 526
452=back 527=back
453 528
454=head2 ARITHMETIC 529=head2 ARITHMETIC
455 530
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479change direction for negative values: 554change direction for negative values:
480 555
481 for (m = -100; m <= 100; ++m) 556 for (m = -100; m <= 100; ++m)
482 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; 557 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
483 558
559=item x = ecb_div_rd (val, div)
560
561=item x = ecb_div_ru (val, div)
562
563Returns C<val> divided by C<div> rounded down or up, respectively.
564C<val> and C<div> must have integer types and C<div> must be strictly
565positive. Note that these functions are implemented with macros in C
566and with function templates in C++.
567
484=back 568=back
485 569
486=head2 UTILITY 570=head2 UTILITY
487 571
488=over 4 572=over 4

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