That's a rather inefficent sieve. Inefficient in the sense that it wastes a lot of memory - it uses a single bit for every number, including all the even ones. That's half the memory usage for numbers you know cannot be prime. I've done sieves based on vec as well, and I've found that the limit on how far you can feasibly go is the memory consumption. Note that any prime number (except the first few) are of the form 30 * n + k with k one of 1, 7, 11, 13, 17, 19, 23, 29. (All other numbers are either divisible by 2, 3 or 5). Which means you need only 8 bits for every 30 numbers. Of course, more efficient packings exist as well.

In reply to Re^2: Find prime number between 1 to 1000000 by JavaFan
in thread Find prime number between 1 to 1000000 by mecrazycoder

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