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Groups > comp.lang.c++ > #91274
| From | "Alf P. Steinbach" <alf.p.steinbach@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: Sieve of Eratosthenes |
| Date | 2023-08-16 23:39 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <ubjfln$3ernq$1@dont-email.me> (permalink) |
| References | <ubijff$3ahf3$1@dont-email.me> <ubjedg$3emtj$1@dont-email.me> |
On 2023-08-16 11:17 PM, Alf P. Steinbach wrote:
> On 2023-08-16 3:37 PM, Bonita Montero wrote:
>> I tried to implement the sieve of Erastosthenes as fast as possible.
>> I didn't thought it would make a big difference, but having a bit-wise
>> vector<bool> instead of a vector<char> makes the code twice as fast
>> for my AMD 7950X PC and an upper bound of one billion. The additional
>> overhead for the bit-wise access is less than the additional overhead
>> of fetching more memory.
>
>
> An apparent mystery, because I get only a marginal difference, down at
> 10% or less.
>
> On my computer the code below is slightly faster than yours for a
> 10'000'000 sieve, respectively (typical results, three runs, only the
> vector allocation + sieve code measured, not file i/o)
>
> 0.0477802 seconds.
> 0.0466974 seconds.
> 0.0472202 seconds.
>
> ... for my code, versus
>
> 0.0502888 seconds.
> 0.0482821 seconds.
> 0.0505414 seconds.
>
> ... for yours with the `std::string_view` instantiations fixed,
> producing the same file contents.
>
>
> #include <fmt/core.h>
> #include "cppm-Timer.hpp"
>
> #include <vector>
> using std::ofstream,
> std::vector;
>
> #include <stdlib.h> // EXIT_FAILURE
> #include <stdio.h> // fopen, fclose
>
> auto main() -> int
> {
> constexpr int n = 10'000'000;
>
> cppm::Timer timer;
> auto is_composite = vector<bool>( n + 1 );
> for( int i = 2; i < n; ) {
> while( is_composite[i] ) { ++i; }
> const int prime = i;
> for( int j = 2*prime; j < n; j += prime ) { is_composite[j]
> = true; }
> ++i;
> }
> timer.stop();
> fmt::print( "{} seconds.\n", timer.seconds() );
>
> auto f = fopen( "primes.alf.txt", "w" );
> if( not f ) { return EXIT_FAILURE; }
> for( int i = 2; i < n; ++i ) {
> if( not is_composite[i] ) {
> fmt::print( f, "{:d}\n", i );
> }
> }
> fclose( f );
> }
>
>
> The timer code:
>
>
> #pragma once
>
> #include <chrono>
> #include <optional>
> #include <type_traits>
>
> namespace cppm {
> namespace chrono = std::chrono;
> using std::optional, // <optional>
> std::conditional_t; // <type_traits>
>
> using Duration = chrono::duration<double>;
>
> class Timer
> {
> using Hrc = chrono::high_resolution_clock; using Sc =
> chrono::steady_clock;
>
> public:
> using Clock = conditional_t<Hrc::is_steady, Hrc, Sc>;
> using Time_point = chrono::time_point<Clock>;
>
> private:
> Time_point m_start_time;
> optional<Time_point> m_opt_end_time;
>
> public:
> Timer(): m_start_time( Clock::now() ), m_opt_end_time() {}
>
> void stop() { if( not m_opt_end_time ) { m_opt_end_time =
> Clock::now(); } }
>
> auto duration() const -> Duration { return
> m_opt_end_time.value() - m_start_time; }
> auto seconds() const -> double { return
> duration().count(); }
> };
> } // namespace cppm
>
>
> I have some other more advanced prime sieve code that I made for an
> example, but I think it's much slower, it's just a way that can go on
> and on forever, or more precisely till the end of the integer type's
> range or it runs out of memory for a map of the deduces primes.
Well, I've become stupid in my old days. Reduced running time by say 25%
or so by very simple optimization. I did not think of that until /after/
I'd posted.
New running time, three tries:
0.0365686 seconds.
0.0362102 seconds.
0.0359283 seconds.
New better shiny sparkling code:
#include <fmt/core.h>
#include "cppm-Timer.hpp"
#include <vector>
using std::vector;
#include <stdlib.h> // EXIT_FAILURE
#include <stdio.h> // fopen, fclose
auto main() -> int
{
constexpr int n = 10'000'000;
constexpr int sqrt_n = 3'162;
cppm::Timer timer;
auto is_composite = vector<bool>( n + 1 );
for( int i = 2; i < n; ) {
while( is_composite[i] ) { ++i; }
const int prime = i;
if( prime < sqrt_n ) {
for( int j = prime*prime; j < n; j += prime ) {
is_composite[j] = true;
}
}
++i;
}
timer.stop();
fmt::print( "{} seconds.\n", timer.seconds() );
auto f = fopen( "primes.alf.txt", "w" );
if( not f ) { return EXIT_FAILURE; }
for( int i = 2; i < n; ++i ) {
if( not is_composite[i] ) {
fmt::print( f, "{:d}\n", i );
}
}
fclose( f );
}
Clue: for efficiency, avoid totally needless work.
- Alf
Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-16 15:37 +0200
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-16 10:57 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-16 20:21 +0200
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-16 12:17 -0700
Re: Sieve of Eratosthenes Paavo Helde <eesnimi@osa.pri.ee> - 2023-08-16 21:44 +0300
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-16 12:09 -0700
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-16 23:17 +0200
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-16 23:21 +0200
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-16 23:39 +0200
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-16 23:59 +0200
Re: Sieve of Eratosthenes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-08-16 16:27 -0700
Re: Sieve of Eratosthenes red floyd <no.spam.here@its.invalid> - 2023-08-16 18:06 -0700
Re: Sieve of Eratosthenes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-08-16 19:26 -0700
Re: Sieve of Eratosthenes Öö Tiib <ootiib@hot.ee> - 2023-08-27 12:26 -0700
Re: Sieve of Eratosthenes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-28 00:49 +0100
Re: Sieve of Eratosthenes Öö Tiib <ootiib@hot.ee> - 2023-08-27 23:23 -0700
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-28 15:53 +0200
Re: Sieve of Eratosthenes Öö Tiib <ootiib@hot.ee> - 2023-08-28 09:03 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-28 18:47 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-30 13:01 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-30 15:38 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-30 18:31 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-31 08:22 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 11:00 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-31 15:23 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 17:28 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 11:52 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-31 15:22 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 17:32 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-31 15:44 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 17:50 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 10:26 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 12:59 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 12:30 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 15:33 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 13:49 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 15:59 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 14:03 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 16:15 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 14:39 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 16:59 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 15:01 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 17:05 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-09-01 15:08 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 17:15 +0200
Re: Sieve of Eratosthenes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-31 21:33 +0100
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-09-01 05:35 +0200
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-31 14:43 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 16:57 +0200
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-31 16:10 +0000
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-31 15:25 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-31 17:33 +0200
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-31 16:12 +0000
Re: Sieve of Eratosthenes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-28 23:08 +0100
Re: Sieve of Eratosthenes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-08-28 15:15 -0700
Re: Sieve of Eratosthenes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-28 23:41 +0100
Re: Sieve of Eratosthenes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-08-30 17:45 -0700
Re: Sieve of Eratosthenes Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-08-31 03:18 +0100
Re: Sieve of Eratosthenes Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-08-28 15:08 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-17 08:42 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-17 11:38 +0200
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-17 12:50 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-17 13:10 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-17 17:47 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-21 11:00 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-21 17:19 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-21 19:50 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-21 18:12 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-21 20:22 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-21 19:01 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 05:27 +0200
Re: Sieve of Eratosthenes Öö Tiib <ootiib@hot.ee> - 2023-08-21 23:25 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 11:23 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 11:59 +0200
Re: Sieve of Eratosthenes Öö Tiib <ootiib@hot.ee> - 2023-08-22 05:15 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 14:23 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 06:56 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 11:27 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 11:34 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 14:13 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 16:17 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 14:27 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 16:48 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 14:57 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 17:00 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 17:56 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 20:13 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 18:18 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-22 20:50 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 06:51 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 09:59 +0200
Re: Sieve of Eratosthenes Richard Damon <Richard@Damon-Family.org> - 2023-08-23 07:52 -0400
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 14:40 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 14:24 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 16:30 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 14:36 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 16:38 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 14:43 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 16:45 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 17:49 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 20:05 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-24 17:18 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-24 19:20 +0200
Re: Sieve of Eratosthenes Daniel <danielaparker@gmail.com> - 2023-08-23 11:13 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 20:17 +0200
Re: Sieve of Eratosthenes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-08-23 11:20 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 20:24 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-24 17:25 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-24 19:29 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-24 17:40 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-24 19:49 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-25 16:07 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 18:10 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-25 16:15 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-25 18:18 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-26 08:03 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-26 10:16 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-26 08:27 +0000
Re: Sieve of Eratosthenes Daniel <danielaparker@gmail.com> - 2023-08-23 11:37 -0700
Re: Sieve of Eratosthenes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-08-26 15:33 -0700
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 14:20 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 16:32 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 14:41 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 16:47 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 17:51 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-23 20:09 +0200
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-23 18:51 +0000
Re: Sieve of Eratosthenes "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-08-24 11:25 -0700
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-24 17:22 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-24 19:27 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-24 17:37 +0000
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-24 19:52 +0200
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-25 16:07 +0000
Re: Sieve of Eratosthenes Daniel <danielaparker@gmail.com> - 2023-08-23 08:00 -0700
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-22 15:49 +0000
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-22 17:58 +0000
Re: Sieve of Eratosthenes scott@slp53.sl.home (Scott Lurndal) - 2023-08-22 18:24 +0000
Re: Sieve of Eratosthenes Muttley@dastardlyhq.com - 2023-08-23 06:50 +0000
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-17 13:43 -0700
Re: Sieve of Eratosthenes "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2023-08-18 02:00 +0200
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-18 05:01 -0700
Re: Sieve of Eratosthenes wij <wyniijj5@gmail.com> - 2023-08-18 17:02 -0700
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-28 06:15 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-28 09:43 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-29 20:34 +0200
Re: Sieve of Eratosthenes Bonita Montero <Bonita.Montero@gmail.com> - 2023-08-30 19:02 +0200
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