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Revision 1.29 by root, Fri Jun 10 12:20:14 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
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101 #else 112 #else
102 return 0; 113 return 0;
103 #endif 114 #endif
104 } 115 }
105 116
106=item ECB_INLINE 117=item ecb_inline
107 118
108This is not actually an attribute, but you use it like one. It expands 119This 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 120either 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, 121supported. It should be used to declare functions that should be inlined,
111for code size or speed reasons. 122for code size or speed reasons.
112 123
113Example: inline this function, it surely will reduce codesize. 124Example: inline this function, it surely will reduce codesize.
114 125
115 ECB_INLINE int 126 ecb_inline int
116 negmul (int a, int b) 127 negmul (int a, int b)
117 { 128 {
118 return - (a * b); 129 return - (a * b);
119 } 130 }
120 131
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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. A common use 432set), 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 433
434For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>.
435
421(n))>. For example: 436For example:
422 437
423 ecb_ctz32 (3) = 0 438 ecb_ctz32 (3) = 0
424 ecb_ctz32 (6) = 1 439 ecb_ctz32 (6) = 1
425 440
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
426=item int ecb_popcount32 (uint32_t x) 466=item int ecb_popcount32 (uint32_t x)
427 467
468=item int ecb_popcount64 (uint64_t x)
469
428Returns 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:
429 475
430 ecb_popcount32 (7) = 3 476 ecb_popcount32 (7) = 3
431 ecb_popcount32 (255) = 8 477 ecb_popcount32 (255) = 8
432 478
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
433=item uint32_t ecb_bswap16 (uint32_t x) 493=item uint32_t ecb_bswap16 (uint32_t x)
434 494
435=item uint32_t ecb_bswap32 (uint32_t x) 495=item uint32_t ecb_bswap32 (uint32_t x)
436 496
497=item uint64_t ecb_bswap64 (uint64_t x)
498
437These 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
438after 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)
439 514
440=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) 515=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
441 516
442=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 517=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
443 518
444These 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
445by 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>).
446 522
447Current GCC versions understand these functions and usually compile them 523Current GCC versions understand these functions and usually compile them
448to "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).
449 526
450=back 527=back
451 528
452=head2 ARITHMETIC 529=head2 ARITHMETIC
453 530
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463C<ecb_mod> implements the mathematical modulo operation, which is missing 540C<ecb_mod> implements the mathematical modulo operation, which is missing
464in the language. 541in the language.
465 542
466C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be 543C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be
467negatable, that is, both C<m> and C<-m> must be representable in its 544negatable, that is, both C<m> and C<-m> must be representable in its
468type (this typically includes the minimum signed integer value, the same 545type (this typically excludes the minimum signed integer value, the same
469limitation as for C</> and C<%> in C). 546limitation as for C</> and C<%> in C).
470 547
471Current GCC versions compile this into an efficient branchless sequence on 548Current GCC versions compile this into an efficient branchless sequence on
472almost all CPUs. 549almost all CPUs.
473 550
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477change direction for negative values: 554change direction for negative values:
478 555
479 for (m = -100; m <= 100; ++m) 556 for (m = -100; m <= 100; ++m)
480 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; 557 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
481 558
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
482=back 568=back
483 569
484=head2 UTILITY 570=head2 UTILITY
485 571
486=over 4 572=over 4

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