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From: Bonita Montero <Bonita.Montero@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: OT: Re: Sieve of Erastosthenes optimized to the max
Date: Tue, 20 Aug 2024 17:24:48 +0200
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Am 20.08.2024 um 17:21 schrieb Bonita Montero:
> Am 19.08.2024 um 22:23 schrieb Vir Campestris:
>> On 16/08/2024 18:35, Bonita Montero wrote:
>> <snip>
>>> But basically I don't think it is a good idea to skip numbers exept
>>> multiples of two. With the three you save a sixth of memory, with
>>> the five you save a 15-th and at the end you get about 20% less
>>> storage (1 / (2 * 3) + 1 / (2 * 3 * 5) + 1 / (2 * 3 * 5 * 7) ...)
>>> for a lot of computation. That's the point where I dropped this
>>> idea and I think this extra computation is higher than the time
>>> for the saved memory loads.
>>>
>> It's not just storage you save, it's also computation.
>>
>> That program I published up-thread is almost as fast as yours - within 
>> 10% of the elapsed time - while only using a single core. The amount 
>> of CPU used is much lower.
>>
>> Andy
> 
> On my AMD 7990X all primes up to 2 ^ 32 are calculated with my code
> with a 65W-setting of the CPU in 0.168s. The total CPU-time is 3.688s.
> With your code all primes up to 2 ^ 32 take nearly exactly four seconds
> with a single thread. So the overall computation time with my algorithm
> is about seconds less.

And if I run my code with a single core:

	C:\Users\Boni\Documents\Source\bitmapSieve>timep 
"x64\Release-clang++\bitmapSieve.exe" 0x100000000 "" 1
	real   1.795s
	user   1.766s
	sys    0.000s
	cylces 8.011.804.500

Thats less than half the computation time.