Timeline for Parallel sieve of Eratosthenes, version 2
Current License: CC BY-SA 3.0
15 events
| when toggle format | what | by | license | comment | |
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| Apr 16, 2014 at 0:00 | comment | added | Ben Voigt | True, I didn't notice they were unsigned | |
| Apr 15, 2014 at 23:26 | comment | added | Morwenn |
@BenVoigt With unsigned integers, -1/prime+1 is generally bigger than prime.
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| Apr 15, 2014 at 23:15 | comment | added | Ben Voigt | @morwenn: even if not, the call to std::max should give the right result | |
| Apr 15, 2014 at 22:42 | comment | added | Morwenn |
@BenVoigt You're right, it works without the special case for 0 if first is initialized with 3u instead of 0u as it is currently the case :)
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| Apr 15, 2014 at 22:23 | comment | added | Ben Voigt | @morwenn: Ok, since you aren't in danger of overflow, (begin+prime-1)/prime. But I thought 0 wasn't a valid concern, since the smallest prime is 2. | |
| Apr 15, 2014 at 22:19 | comment | added | Morwenn |
@BenVoigt Your code works except for begin == 0. It needs either a branch or a saturated subtraction to work.
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| Apr 15, 2014 at 7:43 | vote | accept | Morwenn | ||
| Apr 13, 2014 at 22:02 | comment | added | Morwenn |
@LokiAstari In your code, I suppose that n would be is_prime.size()?
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| Apr 13, 2014 at 21:36 | comment | added | Loki Astari | @BenVoigt: Yes. But integer rounding means that was not enough. Hence the extra conditional. I assume your code works. But have not thought it through. | |
| Apr 13, 2014 at 21:29 | comment | added | Ben Voigt |
I presume that in your original code, you meant for first = begin/prime*prime ?
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| Apr 13, 2014 at 21:26 | history | edited | Loki Astari | CC BY-SA 3.0 |
deleted 9 characters in body
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| Apr 13, 2014 at 21:24 | comment | added | Ben Voigt |
Integer first = std::max((begin-1)/prime + 1, prime)*prime;
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| Apr 13, 2014 at 21:23 | comment | added | Loki Astari | @BenVoigt: Can you expand on that. I am sure you are correct but cant quite place it in the code. | |
| Apr 13, 2014 at 21:21 | comment | added | Ben Voigt |
(begin-1)/prime + 1 would remove a branch. And you're missing a multiply by prime.
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| Apr 13, 2014 at 21:18 | history | answered | Loki Astari | CC BY-SA 3.0 |