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| 412 | |
412 | |
| 413 | On systems that are neither, their return values are unspecified. |
413 | On systems that are neither, their return values are unspecified. |
| 414 | |
414 | |
| 415 | =item int ecb_ctz32 (uint32_t x) |
415 | =item int ecb_ctz32 (uint32_t x) |
| 416 | |
416 | |
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417 | =item int ecb_ctz64 (uint64_t x) |
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418 | |
| 417 | 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 |
| 418 | 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 |
| 419 | set), starting from 0. If C<x> is 0 the result is undefined. For example: |
421 | set), starting from 0. If C<x> is 0 the result is undefined. |
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422 | |
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423 | For example: |
| 420 | |
424 | |
| 421 | ecb_ctz32 (3) = 0 |
425 | ecb_ctz32 (3) = 0 |
| 422 | ecb_ctz32 (6) = 1 |
426 | ecb_ctz32 (6) = 1 |
| 423 | |
427 | |
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428 | =item int ecb_ld32 (uint32_t x) |
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429 | |
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430 | =item int ecb_ld64 (uint64_t x) |
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431 | |
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432 | Returns the index of the most significant bit set in C<x>, or the number |
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433 | of digits the number requires in binary (so that C<< 2**ld <= x < |
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434 | 2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
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435 | to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
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436 | example to see how many bits a certain number requires to be encoded. |
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437 | |
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438 | This function is similar to the "count leading zero bits" function, except |
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439 | that that one returns how many zero bits are "in front" of the number (in |
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440 | the given data type), while C<ecb_ld> returns how many bits the number |
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441 | itself requires. |
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442 | |
| 424 | =item int ecb_popcount32 (uint32_t x) |
443 | =item int ecb_popcount32 (uint32_t x) |
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444 | |
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445 | =item int ecb_popcount64 (uint64_t x) |
| 425 | |
446 | |
| 426 | Returns the number of bits set to 1 in C<x>. For example: |
447 | Returns the number of bits set to 1 in C<x>. For example: |
| 427 | |
448 | |
| 428 | ecb_popcount32 (7) = 3 |
449 | ecb_popcount32 (7) = 3 |
| 429 | ecb_popcount32 (255) = 8 |
450 | ecb_popcount32 (255) = 8 |
