C:\test>rand -N=1e6
...
my $bytes = join '', map chr( unpack( 'V', $rand ) % 256 ), 1 .. $N;
my $set = unpack '%32b*', $bytes;
printf "In $N bytes, there are %d ones and %d zeros\n", $set, length( $bytes ) *8 - $set;

use Statistics::Basic qw[ stddev ];
my @bytes;
++$bytes[ ord( substr $bytes, $_, 1 ) ] for 0 .. length( $bytes ) -1;
#pp \@bytes;
print "Stddev: ", stddev( @bytes );

my %runs;
my $bits = unpack 'b*', $bytes;
for my $n ( 2 .. 40 ) {
    ++$runs{ length() } for $bits =~ m[(?<=0)(1{$n})(?=0)]g;
}
pp \%runs;

__END__
C:\test>rand -N=1e6
In 1e6 bytes, there are 4000292 ones and 3999708 zeros
Stddev: 191.23
{ 2 => 500474, 3 => 249154, 4 => 124655, 5 => 61747, 6 => 31528, 7 => 25885, 8 => 4672, 9 => 656, 10 => 175, 11 => 42, 12 => 17, 13 => 16, 14 => 18, 15 => 13, 16 => 91, 17 => 38, 18 => 21, 19 => 13, 20 => 10, 21 => 6, 22 => 5, 23 => 9, 24 => 50, 25 => 23, 26 => 17, 27 => 5, 28 => 6, 29 => 2, 30 => 2, 31 => 3, 32 => 37, 33 => 21, 34 => 9, 35 => 2, 36 => 2, 38 => 4, 39 => 5, 40 => 29 }


C:\test>rand -N=1e6
In 1e6 bytes, there are 3991425 ones and 4008575 zeros
Stddev: 197.76
{ 2 => 500058, 3 => 248757, 4 => 124893, 5 => 62380, 6 => 30268, 7 => 24800, 8 => 4693, 9 => 582, 10 => 153, 11 => 59, 12 => 26, 13 => 13, 14 => 10, 15 => 11, 16 => 108, 17 => 45, 18 => 14, 19 => 11, 20 => 5, 21 => 8, 22 => 7, 23 => 2, 24 => 46, 25 => 13, 26 => 10, 27 => 6, 28 => 5, 29 => 3, 30 => 3, 31 => 1, 32 => 50, 33 => 10, 34 => 6, 35 => 3, 36 => 5, 37 => 3, 38 => 1, 39 => 1, 40 => 40 }