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Revision 1.27 by root, Wed Jun 1 01:29:36 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
117=item ecb_inline
118
119This is not actually an attribute, but you use it like one. It expands
120either to C<static inline> or to just C<static>, if inline isn't
121supported. It should be used to declare functions that should be inlined,
122for code size or speed reasons.
123
124Example: inline this function, it surely will reduce codesize.
125
126 ecb_inline int
127 negmul (int a, int b)
128 {
129 return - (a * b);
130 }
131
106=item ecb_noinline 132=item ecb_noinline
107 133
108Prevent a function from being inlined - it might be optimised away, but 134Prevent a function from being inlined - it might be optimised away, but
109not inlined into other functions. This is useful if you know your function 135not inlined into other functions. This is useful if you know your function
110is rarely called and large enough for inlining not to be helpful. 136is rarely called and large enough for inlining not to be helpful.
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381After 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
382cache. 408cache.
383 409
384=back 410=back
385 411
386=head2 BIT FIDDLING / BITSTUFFS 412=head2 BIT FIDDLING / BIT WIZARDRY
387 413
388=over 4 414=over 4
389 415
390=item bool ecb_big_endian () 416=item bool ecb_big_endian ()
391 417
… …
397 423
398On systems that are neither, their return values are unspecified. 424On systems that are neither, their return values are unspecified.
399 425
400=item int ecb_ctz32 (uint32_t x) 426=item int ecb_ctz32 (uint32_t x)
401 427
428=item int ecb_ctz64 (uint64_t x)
429
402Returns 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
403equivalently 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
404set), 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.
405case 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
406(n))>. For example: 436For example:
407 437
408 ecb_ctz32 (3) = 0 438 ecb_ctz32 (3) = 0
409 ecb_ctz32 (6) = 1 439 ecb_ctz32 (6) = 1
410 440
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
411=item int ecb_popcount32 (uint32_t x) 466=item int ecb_popcount32 (uint32_t x)
412 467
468=item int ecb_popcount64 (uint64_t x)
469
413Returns 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:
414 475
415 ecb_popcount32 (7) = 3 476 ecb_popcount32 (7) = 3
416 ecb_popcount32 (255) = 8 477 ecb_popcount32 (255) = 8
417 478
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
418=item uint32_t ecb_bswap16 (uint32_t x) 493=item uint32_t ecb_bswap16 (uint32_t x)
419 494
420=item uint32_t ecb_bswap32 (uint32_t x) 495=item uint32_t ecb_bswap32 (uint32_t x)
421 496
497=item uint64_t ecb_bswap64 (uint64_t x)
498
422These 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
423after 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)
424 514
425=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) 515=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count)
426 516
427=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) 517=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count)
428 518
429These 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
430by 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>).
431 522
432Current GCC versions understand these functions and usually compile them 523Current GCC versions understand these functions and usually compile them
433to "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).
434 526
435=back 527=back
436 528
437=head2 ARITHMETIC 529=head2 ARITHMETIC
438 530
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448C<ecb_mod> implements the mathematical modulo operation, which is missing 540C<ecb_mod> implements the mathematical modulo operation, which is missing
449in the language. 541in the language.
450 542
451C<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
452negatable, 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
453type (this typically includes the minimum signed integer value, the same 545type (this typically excludes the minimum signed integer value, the same
454limitation as for C</> and C<%> in C). 546limitation as for C</> and C<%> in C).
455 547
456Current GCC versions compile this into an efficient branchless sequence on 548Current GCC versions compile this into an efficient branchless sequence on
457many systems. 549almost all CPUs.
458 550
459For example, when you want to rotate forward through the members of an 551For example, when you want to rotate forward through the members of an
460array for increasing C<m> (which might be negative), then you should use 552array for increasing C<m> (which might be negative), then you should use
461C<ecb_mod>, as the C<%> operator might give either negative results, or 553C<ecb_mod>, as the C<%> operator might give either negative results, or
462change direction for negative values: 554change direction for negative values:
463 555
464 for (m = -100; m <= 100; ++m) 556 for (m = -100; m <= 100; ++m)
465 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; 557 int elem = myarray [ecb_mod (m, ecb_array_length (myarray))];
466 558
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
467=back 568=back
468 569
469=head2 UTILITY 570=head2 UTILITY
470 571
471=over 4 572=over 4

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