Eratosthenes was a clever chap!
use strict;
use warnings;
use Benchmark qw{ cmpthese };
use Test::More tests => 1;
is_deeply(
[ primes( 10000 ) ],
[ primes_jg( 10000 ) ],
'same'
);
cmpthese(
-10,
{
ch => 'primes( 10000 )',
jg => 'primes_jg( 10000 )',
}
);
sub primes_jg
{
my $limit = shift;
my $sqrtLimit = sqrt $limit;
my $sieve = q{};
vec( $sieve, 0, 1 ) = 1;
vec( $sieve, 1, 1 ) = 1;
vec( $sieve, $limit, 1 ) = 0;
my @primes;
my $reached = 1;
while( $reached < $sqrtLimit )
{
my $prime = $reached + 1;
++ $prime while vec( $sieve, $prime, 1 );
push @primes, $prime;
my $fill = 2 * $prime;
while( $fill <= $limit )
{
vec( $sieve, $fill, 1 ) = 1;
$fill += $prime;
}
$reached = $prime;
}
foreach my $value ( $reached + 1 .. $limit )
{
push @primes, $value unless vec( $sieve, $value, 1 );
}
return @primes;
}
sub primes {
my $n = shift;
return if $n < 2;
my @primes = (2);
for my $i (3 .. $n) {
my $sqrt = sqrt $i;
my $notprime;
for my $p (@primes) {
last if $p > $sqrt;
$notprime = 1, last if 0 == $i % $p;
}
push @primes, $i unless $notprime;
}
return @primes
}
1..1
ok 1 - same
Rate ch jg
ch 71.0/s -- -25%
jg 94.7/s 33% --
I hope this is of interest.
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