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User talk:Daveb: Difference between revisions
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I just open the caliper case, cut the battery trace (which one doesn’t matter), drill two holes to allow the fine (wire wrap) wire to come out the top to a micro-miniature slide switch glued to the top. I always turn the switch off, rather than press some caliper “off” button, and find that a button cell lasts for many years. I would attach a picture if Sparkfun allowed, but it doesn’t. Caliper thickness is unchanged, and the outline is very nearly unchanged. | I just open the caliper case, cut the battery trace (which one doesn’t matter), drill two holes to allow the fine (wire wrap) wire to come out the top to a micro-miniature slide switch glued to the top. I always turn the switch off, rather than press some caliper “off” button, and find that a button cell lasts for many years. I would attach a picture if Sparkfun allowed, but it doesn’t. Caliper thickness is unchanged, and the outline is very nearly unchanged. | ||
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|'''prime number generator'''|| thought || Invert the sieve of Aristophanes, so the data structure holds primes and the next multiple of each prime. Keep the data-structure sorted by the next multiple. When a gap occurs between the current nearest multiple and the next nearest the gap contains prime number(s). | |'''prime number generator'''|| silly thought || Invert the sieve of Aristophanes, so the data structure holds primes and the next multiple of each prime. Keep the data-structure sorted by the next multiple. When a gap occurs between the current nearest multiple and the next nearest the gap contains prime number(s). | ||
The algorithm requires sorting subsequent multiples into place. | The algorithm requires sorting subsequent multiples into place. | ||
If N is the number of discovered primes N, and the size of the primes is S: | If N is the number of discovered primes N, and the size of the primes is S: | ||
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cpu use is O(S*N*N) | cpu use is O(S*N*N) | ||
Other | Other thoughts: | ||
* use wheel factorisation of the first M primes to compactly and efficiently represent the impact of these first M primes, where M is chosen so the product of these primes fit in a machine word, and so that the primes less than the product fit in affordable memory. | * use wheel factorisation of the first M primes to compactly and efficiently represent the impact of these first M primes, where M is chosen so the product of these primes fit in a machine word, and so that the primes less than the product fit in affordable memory. | ||
* use interval arithmetic to keep track of the intermediate numbers. | * use interval arithmetic to keep track of the intermediate numbers. | ||
* can it be fitted to hardware? | * can it be fitted to hardware? | ||
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|'''factorisation'''|| silly thought || By trial division using list of known primes; is exceedingly slow for large numbers; the number of potential factors is O(sqrt(N)) - if N is more than 100 bits that is a big number. However, can knowledge of the factors be used to restrict the search space usefully? What are the constraints on the factors imposed by PGP for example | |||
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