| … | |
… | |
| 100 | return var; |
100 | return var; |
| 101 | #else |
101 | #else |
| 102 | return 0; |
102 | return 0; |
| 103 | #endif |
103 | #endif |
| 104 | } |
104 | } |
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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 | } |
| 105 | |
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 |
| … | |
… | |
| 399 | |
414 | |
| 400 | =item int ecb_ctz32 (uint32_t x) |
415 | =item int ecb_ctz32 (uint32_t x) |
| 401 | |
416 | |
| 402 | Returns the index of the least significant bit set in C<x> (or |
417 | 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 |
418 | 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 |
419 | set), starting from 0. If C<x> is 0 the result is undefined. For example: |
| 405 | case is to compute the integer binary logarithm, i.e., C<floor (log2 |
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| 406 | (n))>. For example: |
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| 407 | |
420 | |
| 408 | ecb_ctz32 (3) = 0 |
421 | ecb_ctz32 (3) = 0 |
| 409 | ecb_ctz32 (6) = 1 |
422 | ecb_ctz32 (6) = 1 |
| 410 | |
423 | |
| 411 | =item int ecb_popcount32 (uint32_t x) |
424 | =item int ecb_popcount32 (uint32_t x) |
| … | |
… | |
| 448 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
461 | C<ecb_mod> implements the mathematical modulo operation, which is missing |
| 449 | in the language. |
462 | in the language. |
| 450 | |
463 | |
| 451 | C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
464 | 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 |
465 | 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 |
466 | type (this typically excludes the minimum signed integer value, the same |
| 454 | limitation as for C</> and C<%> in C). |
467 | limitation as for C</> and C<%> in C). |
| 455 | |
468 | |
| 456 | Current GCC versions compile this into an efficient branchless sequence on |
469 | Current GCC versions compile this into an efficient branchless sequence on |
| 457 | many systems. |
470 | almost all CPUs. |
| 458 | |
471 | |
| 459 | For example, when you want to rotate forward through the members of an |
472 | 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 |
473 | 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 |
474 | C<ecb_mod>, as the C<%> operator might give either negative results, or |
| 462 | change direction for negative values: |
475 | change direction for negative values: |
