Re: Hash limits? (Was: Re: rand() not so random)
At 10:53 AM 12/1/2005 -0500, Ted Schuerzinger wrote:
Just for fun, I changed one of the lines in that to
for (1 .. 100) {
When I ran the modified script, I got 32768 unique numbers, with 967232
duplicates! As 32768 is a power of 2, I'm wondering if there's a limit on
the number of keys one may have in a hash.
Heh, I did that too, but kept it a secret. That tells me rand is a very
weak function. I think the 2^15 answer u got is a coincidence. Do it 5
times, u'll get 5 answers. It doesn't have anything to do with the hash
itself. (AFAIK) It only gets invoked upon a *duplicate*, not a unique. The
no. of keys is 967232.
--
REMEMBER THE WORLD TRADE CENTER ---= WTC 911 =--
...ne cede malis
0100
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Re: Hash limits? (Was: Re: rand() not so random)
Wait, I screwed up that last email. The uniques is the number of hash keys.
At 10:53 AM 12/1/2005 -0500, Ted Schuerzinger wrote:
for (1 .. 1) {
my $fn = rand();
++$dup and next if exists $num{$fn};
$num{$fn} = 1;
}
print scalar keys %num, unique numbers. $dup duplicates produced\n;
Just for fun, I changed one of the lines in that to
for (1 .. 100) {
When I ran the modified script, I got 32768 unique numbers, with 967232
duplicates! As 32768 is a power of 2, I'm wondering if there's a limit on
the number of keys one may have in a hash.
--
REMEMBER THE WORLD TRADE CENTER ---= WTC 911 =--
...ne cede malis
0100
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Re: Hash limits? (Was: Re: rand() not so random)
On Thu, 1 Dec 2005 12:05:11 -0800, you wrote:
[EMAIL PROTECTED] (Chris Wagner) graced perl with these words of
wisdom:
Just for fun I did a little test.
for (1 .. 1) {
my $fn = rand();
++$dup and next if exists $num{$fn};
$num{$fn} = 1;
}
print scalar keys %num, unique numbers. $dup duplicates produced\n;
Just for fun, I changed one of the lines in that to
for (1 .. 100) {
When I ran the modified script, I got 32768 unique numbers, with 967232
duplicates! As 32768 is a power of 2, I'm wondering if there's a limit on
the number of keys one may have in a hash.
No, it's a limit on the number of values rand() produces on Windows, as
this one-liner shows:
perl -MConfig -e print $Config{randbits}
randbits is the number of bits in the value produced by rand(); the
value is 15 in ActiveState Perl for Windows. If you want a better random
number generator, there are modules available on the PPM repositories;
search for random.
--
Eric Amick
Columbia, MD
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Re: Hash limits? (Was: Re: rand() not so random)
- Original Message -
From: Ted Schuerzinger [EMAIL PROTECTED]
To: Perl-Win32-Users@listserv.ActiveState.com
Sent: Friday, December 02, 2005 2:53 AM
Subject: Hash limits? (Was: Re: rand() not so random)
[EMAIL PROTECTED] (Chris Wagner) graced perl with these words of
wisdom:
Just for fun I did a little test.
for (1 .. 1) {
my $fn = rand();
++$dup and next if exists $num{$fn};
$num{$fn} = 1;
}
print scalar keys %num, unique numbers. $dup duplicates produced\n;
Just for fun, I changed one of the lines in that to
for (1 .. 100) {
When I ran the modified script, I got 32768 unique numbers, with 967232
duplicates! As 32768 is a power of 2, I'm wondering if there's a limit on
the number of keys one may have in a hash.
I think it's just that there are only 2 ** $Config{randbits} distinct
numbers that rand() will output.
You'll probably find that $Config{randbits} for you is 15 and 2 ** 15
== 32768.
ie, with 15 bits, you can represent only 32768 different numbers.
Cheers,
Rob
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RE: Hash limits? (Was: Re: rand() not so random)
On Thu, 01 Dec 2005, Ted Schuerzinger wrote:
Just for fun I did a little test.
for (1 .. 1) {
my $fn = rand();
++$dup and next if exists $num{$fn};
$num{$fn} = 1;
}
print scalar keys %num, unique numbers. $dup duplicates produced\n;
Just for fun, I changed one of the lines in that to
for (1 .. 100) {
When I ran the modified script, I got 32768 unique numbers, with 967232
duplicates! As 32768 is a power of 2, I'm wondering if there's a limit on
the number of keys one may have in a hash.
No, there isn't. But rand() uses only 15 bits in the default implementation,
so you cannot generate more than 2**15 different values:
C:perl -V:randbits
randbits='15';
Cheers,
-Jan
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