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101 | #else |
101 | #else |
102 | return 0; |
102 | return 0; |
103 | #endif |
103 | #endif |
104 | } |
104 | } |
105 | |
105 | |
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106 | =item ecb_inline |
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107 | |
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108 | This is not actually an attribute, but you use it like one. It expands |
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109 | either to C<static inline> or to just C<static>, if inline isn't |
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110 | supported. It should be used to declare functions that should be inlined, |
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111 | for code size or speed reasons. |
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112 | |
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113 | Example: inline this function, it surely will reduce codesize. |
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114 | |
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115 | ecb_inline int |
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116 | negmul (int a, int b) |
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117 | { |
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118 | return - (a * b); |
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119 | } |
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120 | |
106 | =item ecb_noinline |
121 | =item ecb_noinline |
107 | |
122 | |
108 | Prevent a function from being inlined - it might be optimised away, but |
123 | Prevent a function from being inlined - it might be optimised away, but |
109 | not inlined into other functions. This is useful if you know your function |
124 | not inlined into other functions. This is useful if you know your function |
110 | is rarely called and large enough for inlining not to be helpful. |
125 | is rarely called and large enough for inlining not to be helpful. |
… | |
… | |
381 | After processing the node, (part of) the next node might already be in |
396 | After processing the node, (part of) the next node might already be in |
382 | cache. |
397 | cache. |
383 | |
398 | |
384 | =back |
399 | =back |
385 | |
400 | |
386 | =head2 BIT FIDDLING / BITSTUFFS |
401 | =head2 BIT FIDDLING / BIT WIZARDRY |
387 | |
402 | |
388 | =over 4 |
403 | =over 4 |
389 | |
404 | |
390 | =item bool ecb_big_endian () |
405 | =item bool ecb_big_endian () |
391 | |
406 | |
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397 | |
412 | |
398 | On systems that are neither, their return values are unspecified. |
413 | On systems that are neither, their return values are unspecified. |
399 | |
414 | |
400 | =item int ecb_ctz32 (uint32_t x) |
415 | =item int ecb_ctz32 (uint32_t x) |
401 | |
416 | |
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417 | =item int ecb_ctz64 (uint64_t x) |
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418 | |
402 | Returns the index of the least significant bit set in C<x> (or |
419 | Returns the index of the least significant bit set in C<x> (or |
403 | equivalently the number of bits set to 0 before the least significant bit |
420 | equivalently the number of bits set to 0 before the least significant bit |
404 | set), starting from 0. If C<x> is 0 the result is undefined. A common use |
421 | set), starting from 0. If C<x> is 0 the result is undefined. |
405 | case is to compute the integer binary logarithm, i.e., C<floor (log2 |
422 | |
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423 | For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
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424 | |
406 | (n))>. For example: |
425 | For example: |
407 | |
426 | |
408 | ecb_ctz32 (3) = 0 |
427 | ecb_ctz32 (3) = 0 |
409 | ecb_ctz32 (6) = 1 |
428 | ecb_ctz32 (6) = 1 |
410 | |
429 | |
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430 | =item int ecb_ld32 (uint32_t x) |
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431 | |
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432 | =item int ecb_ld64 (uint64_t x) |
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433 | |
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434 | Returns the index of the most significant bit set in C<x>, or the number |
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435 | of digits the number requires in binary (so that C<< 2**ld <= x < |
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436 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
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437 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
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438 | example to see how many bits a certain number requires to be encoded. |
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439 | |
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440 | This function is similar to the "count leading zero bits" function, except |
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441 | that that one returns how many zero bits are "in front" of the number (in |
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442 | the given data type), while C<ecb_ld> returns how many bits the number |
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443 | itself requires. |
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444 | |
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445 | For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
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446 | |
411 | =item int ecb_popcount32 (uint32_t x) |
447 | =item int ecb_popcount32 (uint32_t x) |
412 | |
448 | |
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449 | =item int ecb_popcount64 (uint64_t x) |
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450 | |
413 | Returns the number of bits set to 1 in C<x>. For example: |
451 | Returns the number of bits set to 1 in C<x>. |
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452 | |
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453 | For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
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454 | |
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455 | For example: |
414 | |
456 | |
415 | ecb_popcount32 (7) = 3 |
457 | ecb_popcount32 (7) = 3 |
416 | ecb_popcount32 (255) = 8 |
458 | ecb_popcount32 (255) = 8 |
417 | |
459 | |
418 | =item uint32_t ecb_bswap16 (uint32_t x) |
460 | =item uint32_t ecb_bswap16 (uint32_t x) |
419 | |
461 | |
420 | =item uint32_t ecb_bswap32 (uint32_t x) |
462 | =item uint32_t ecb_bswap32 (uint32_t x) |
421 | |
463 | |
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464 | =item uint64_t ecb_bswap64 (uint64_t x) |
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465 | |
422 | These two functions return the value of the 16-bit (32-bit) value C<x> |
466 | These functions return the value of the 16-bit (32-bit, 64-bit) value |
423 | after reversing the order of bytes (0x11223344 becomes 0x44332211). |
467 | C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
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468 | C<ecb_bswap32>). |
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469 | |
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470 | =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
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471 | |
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472 | =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
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473 | |
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474 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
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475 | |
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476 | =item uint64_t ecb_rotl64 (uint64_t x, unsigned int count) |
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477 | |
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478 | =item uint8_t ecb_rotr8 (uint8_t x, unsigned int count) |
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479 | |
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480 | =item uint16_t ecb_rotr16 (uint16_t x, unsigned int count) |
424 | |
481 | |
425 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
482 | =item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
426 | |
483 | |
427 | =item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
484 | =item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
428 | |
485 | |
429 | These two functions return the value of C<x> after rotating all the bits |
486 | These two families of functions return the value of C<x> after rotating |
430 | by C<count> positions to the right or left respectively. |
487 | all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
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488 | (C<ecb_rotl>). |
431 | |
489 | |
432 | Current GCC versions understand these functions and usually compile them |
490 | Current GCC versions understand these functions and usually compile them |
433 | to "optimal" code (e.g. a single C<roll> on x86). |
491 | to "optimal" code (e.g. a single C<rol> or a combination of C<shld> on |
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492 | x86). |
434 | |
493 | |
435 | =back |
494 | =back |
436 | |
495 | |
437 | =head2 ARITHMETIC |
496 | =head2 ARITHMETIC |
438 | |
497 | |
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448 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
507 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
449 | in the language. |
508 | in the language. |
450 | |
509 | |
451 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
510 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
452 | negatable, that is, both C<m> and C<-m> must be representable in its |
511 | negatable, that is, both C<m> and C<-m> must be representable in its |
453 | type (this typically includes the minimum signed integer value, the same |
512 | type (this typically excludes the minimum signed integer value, the same |
454 | limitation as for C</> and C<%> in C). |
513 | limitation as for C</> and C<%> in C). |
455 | |
514 | |
456 | Current GCC versions compile this into an efficient branchless sequence on |
515 | Current GCC versions compile this into an efficient branchless sequence on |
457 | many systems. |
516 | almost all CPUs. |
458 | |
517 | |
459 | For example, when you want to rotate forward through the members of an |
518 | For example, when you want to rotate forward through the members of an |
460 | array for increasing C<m> (which might be negative), then you should use |
519 | array for increasing C<m> (which might be negative), then you should use |
461 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
520 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
462 | change direction for negative values: |
521 | change direction for negative values: |
463 | |
522 | |
464 | for (m = -100; m <= 100; ++m) |
523 | for (m = -100; m <= 100; ++m) |
465 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
524 | int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
466 | |
525 | |
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526 | =item x = ecb_div_rd (val, div) |
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527 | |
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528 | =item x = ecb_div_ru (val, div) |
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529 | |
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530 | Returns C<val> divided by C<div> rounded down or up, respectively. |
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531 | C<val> and C<div> must have integer types and C<div> must be strictly |
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532 | positive. |
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533 | |
467 | =back |
534 | =back |
468 | |
535 | |
469 | =head2 UTILITY |
536 | =head2 UTILITY |
470 | |
537 | |
471 | =over 4 |
538 | =over 4 |