The following is a slight modification of your program. It (ab)uses the fact that Perl only checks whether to split buckets when you use a new bucket. It does not make any assumptions about Perl's hashing algorithm. It is therefore able to generate the special keys much more quickly than yours does. 
my $HOW_MANY = shift || 100_000;

my ($s, $e1, $e2);
$s = time;
for ($i=0; $i<$HOW_MANY; $i++) {
  $q{$i}=1;
}
$e1 = time - $s;
print qq{
Normally, it takes me about $e1 second(s) to put $HOW_MANY items into 
+a
hash.  Now I'm going to construct $HOW_MANY special keys and see 
how long it takes to put those into a hash instead.
};
undef %q;

print "Generating $HOW_MANY keys\n";
my @keys;
my $i = 0;
while (@keys < $HOW_MANY) {
  $i++;
  my %hash = (0 => 0, $i => 0);
  if (%hash =~ /1/) {
    # Goes in the same bucket as 0
    push @keys, $i;
  }
}

print "Putting the $HOW_MANY special keys into the hash.\n";
$i = 0;
$lasttime = $s = time;
foreach $key (@keys) {
  $h{$key} = 1;
  
  $i++;
  
  if (time() - $lasttime  > 5) {
    my $h = %h + 0;
    print "I have put $i keys into the hash, using $h bucket(s)\n" ;
    $lasttime = time;
  }
}

$e2 = time - $s;
print qq{
The $HOW_MANY special keys took $e2 seconds to put into the hash,
instead of $e1 seconds.
};

[download]

Update: (Much later.) Perl changed when it splits buckets so this program no longer runs slowly. Furthermore Perl's hashing algorithm is now random, so Dominus' program no longer runs slowly. Shucks.

In reply to Re: Re: Shift, Pop, Unshift and Push with Impunity! by tilly
in thread Shift, Pop, Unshift and Push with Impunity! by lhoward

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