晋太元中,武陵人捕鱼为业。缘溪行,忘路之远近。忽逢桃花林,夹岸数百步,中无杂树,芳草鲜美,落英缤纷。渔人甚异之,复前行,欲穷其林。 林尽水源,便得一山,山有小口,仿佛若有光。便舍船,从口入。初极狭,才通人。复行数十步,豁然开朗。土地平旷,屋舍俨然,有良田、美池、桑竹之属。阡陌交通,鸡犬相闻。其中往来种作,男女衣着,悉如外人。黄发垂髫,并怡然自乐。 见渔人,乃大惊,问所从来。具答之。便要还家,设酒杀鸡作食。村中闻有此人,咸来问讯。自云先世避秦时乱,率妻子邑人来此绝境,不复出焉,遂与外人间隔。问今是何世,乃不知有汉,无论魏晋。此人一一为具言所闻,皆叹惋。余人各复延至其家,皆出酒食。停数日,辞去。此中人语云:“不足为外人道也。”(间隔 一作:隔绝) 既出,得其船,便扶向路,处处志之。及郡下,诣太守,说如此。太守即遣人随其往,寻向所志,遂迷,不复得路。 南阳刘子骥,高尚士也,闻之,欣然规往。未果,寻病终。后遂无问津者。
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#!/usr/bin/perl -w
BEGIN { unshift @INC, '../lib'; } # uncomment to use old, org version
$| = 1;
use Math::BigInt;
# this is a complicated version of the prime number sieve.
# It is not optimized (since we want to benchmark as many features as
# possible).
$amount = Math::BigInt->new( shift || 1000000 );
@primes = (1,1,0); # any not defined number is prime, 0,1 are not, but 2 is
my $prime = Math::BigInt->new (3); # start
# the loop below is faster in the old version than in the new, since it is
# the worst case for new lib: small numbers and lot's of bstr()/new().
# It also slows down the benchmark too much so we use slightly faster int here
$r = 0; my $a = $amount->numify();
for ($i = 3; $i < $a; $i++) # int version
{
$primes[$i] = $r; $r = 1-$r;
}
# find primes
OUTER:
while ($prime < $amount)
{
# find first unmarked, it is the next prime
$cur = $prime;
while ($primes[$cur])
{
$cur += 2; last OUTER if $cur >= $amount; # no more to do
}
# $cur is now new prime
$str = "$cur"; $str =~ s/\+//; # unify output for comapre
#print "$str $prime $amount\n";
# now strike out all multiples of $cur
$add = $cur*2;
$prime = $cur + 2; # next round start two higher
$cur += $add;
while ($cur < $amount)
{
$primes[$cur] = 1; $cur += $add;
}
}
$i = 0;
foreach (@primes)
{
push @real_primes, $i if $primes[$i] == 0;
$i++;
}
# uncomment to print em:
# foreach (@real_primes) { print "$_\n"; }
print "last prime: $real_primes[-1]\n";
# check against text
open FILE, '1000.txt' or die "Can't read 1000.txt: $!";
my @test;
while (<FILE>)
{
next if /^#/;
next if /^\s*$/;
$_ =~ s/\s+/ /g;
$_ =~ s/^\s+//;
$_ =~ s/\s+$//;
push @test, split /\s+/,$_;
}
close FILE;
my $i = 0;
foreach (@real_primes)
{
print "oups: $i: $test[$i] != $real_primes[$i]\n"
if $test[$i] != $real_primes[$i]; $i++;
last if $i >= 1000;
}
print "done\n";