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- Subject: Re: Sieve of Eratosthenes performance question
- From: "Shoaib Meenai" <shobiz91@...>
- Date: Thu, 7 Jun 2007 00:05:57 +0500
On 6/6/07, Rici Lake <email@example.com> wrote:
On 6-Jun-07, at 1:27 PM, Shoaib Meenai wrote:
> On 6/6/07, Philippe Lhoste <PhiLho@gmx.net> wrote:
>> ... I believe the difference is because I made 'composite' an array
>> contiguous numerical indexes, with optimized access in Lua 5.1 (direct
>> offset computing), while in the previous code, Lua probably has to
>> more complex tests (hashing the index?) to see if the slot is empty
> Might be a stupid question, but would the optimization apply even if
> the first index was, say, 1296?
Probably not. The optimization requires (roughly) that the array uses
than half of the indices in the range [1, 2^k] for some integer k (and
applies to the indices in that range: anything outside of the range is
stored in the hash part of the table).
But if I used, for example, indices 1296 to 65536 (which is 2^16),
would the optimization apply? Or does k have some preset value which
varies from system to system?