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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: OT: Re: Sieve of Erastosthenes optimized to the max
Date: Fri, 16 Aug 2024 07:48:07 -0700
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Vir Campestris <vir.campestris@invalid.invalid> writes:

> (replying to two messages at once)
>
> On 10/08/2024 15:07, Tim Rentsch wrote:
>
>>> I suspect the cost of extracting the divided value from the 7
>>> bytes will be prohibitive.  You may find it's best to have one
>>> table for the N/30 parts (big entries, word aligned) and another
>>> for the N%30 part (small entries, byte aligned).  BICBW.
>>
>> Two tables, absolutely.  What does BICBW stand for?
>
> But I Could Be Wrong.  I thought that one was fairly well known.

Ah.  No wonder I didn't know it. ;)

> On 11/08/2024 08:00, Tim Rentsch wrote:
>
>> Note that the %30 tables can be shared.  There are 8 of them, one
>> for each of the eight residues mod 30 of the original prime.
>
> I started coding that up.  Then it occurred to me that there wasn't
> going to be much saving by storing a pointer (8 bytes on my machine)
> to the correct 8-byte long table.  I suppose I could store a byte array
> index instead, but I've gone off in other directions.

Right, I was meaning keeping track of the index, not a pointer.

> You've picked up my cache management tweak.

It's an interesting idea, although I'm not sure how well it
integrates with what I've done.

> I'll read through your code.  But it might not be today.  We've got the
> hottest day of the year here, and I don't have aircon in my garden
> office.  In winter the computer and me are enough to keep it warm, but
> right now it's getting warmer by the minute.

My sympathies.  I too find it hard to work when it's too hot.

I see you have started looking at my code... I'll take a look.