64 bit numbers in a 32 bit world.

TedYoung has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am using perl 5.8.4 (compiled 32 bit). I want to create 64 bit numbers and insert them into a mysql db using DBI. Until now, I have always used mysql's bigint column (64 bit int) with Perl/DBI with no problem. But, I never actually used numbers greater than 32 bits. Now I need to.

Is there a way to create a number between 1 << 32 and 1 << 64 without using bigint? I don't have any reason not to use bigint, other than I don't need infinite precision, and would expect (emulated) 64 bit arithmetic to be faster. That may not actually be true, though.

So, I asked DBI and DBD::mysql what they thought about this. Here is my code. The comments show the output of each print.

use DBI;
use Data::Dumper;

my $db = DBI->connect("DBI:mysql:dev", '*****', '******', { RaiseError
+ => 1 });

$db->do("drop table test");
$db->do("create table test (foo bigint)");

print '---------------------------------------------';

do {
    use bigint; # Need this to make larger numbers
    my $i = 1 << 62;
    print $i; # 4611686018427387904
    print ref $i; # Math::BigInt
    $db->do('insert into test values(?)', {}, $i);
};

print '---------------------------------------------';

do {
    my $a = $db->selectrow_arrayref('select * from test');
    my $i = $a->[0];
    print $i; # 4611686018427387904
    print ref $i; # <blank>
    print 0 + $i; # 4.61168601842739e+18
};
[download]

Some comments: The last statement (0 + $i) rounds the number to a floating point if I don't use bigint (as expected). But, printing $i still seems to hold the large number despite $i not being a Math::BigInt. Even using biging in the second do does not cast the $i to a Math::BigInt (but at least arithmetic works).

How does DBI make that? <whine>I want to too!!!</whine>

FWIW, perlop says the shift opts are undefined for counts larger than 31 outside of bigint

Update: Thanks monks! I am not sure why string didn't occur to me! That makes a lot of sense. I will check out Math::Int64 too.

Thanks,

Ted Young

($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)

Comment on 64 bit numbers in a 32 bit world. Select or Download Code

Replies are listed 'Best First'.
Re: 64 bit numbers in a 32 bit world. by salva (Canon) on Apr 24, 2007 at 21:11 UTC
A couple of weeks ago I released Math::Int64 that does exactly what you ask for. Though it is yet not stable, may contain bugs and requires 64bits support from the C compiler.	[reply]
Re: 64 bit numbers in a 32 bit world. by ikegami (Patriarch) on Apr 24, 2007 at 21:07 UTC
But, printing $i still seems to hold the large number despite $i not being a Math::BigInt. I'm betting `$i` is just a string. `useDevel::Peek; Dump($i);` would confirm that. Two pedantic notes, Your `do { ... };` blocks could have been written as `{ ... }`. It would make a difference if you used `next`, `redo` or `last` in the block, however. I don't see anything that says that bignum is lexically scoped. It's misleading to place it in a block if it's not.	[reply] [d/l] [select]
Re^2: 64 bit numbers in a 32 bit world. by TedYoung (Deacon) on Apr 25, 2007 at 02:31 UTC
I couldn't find anything about bignum being lexically scoped either, but try: `{ use bignum; print ref 1; # Math::BigInt } { print ref 1; # <blank> }` [download] Perl just dwim. Ted Young `($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)`	[reply] [d/l] [select]
Re: 64 bit numbers in a 32 bit world. by rodion (Chaplain) on Apr 24, 2007 at 21:11 UTC
I believe DBI is returning a string to you, which Perl has no trouble representing. If it's already a string, print can easily display it. I think you would have trouble if you tried to display it with "printf('%20d', $i);".	[reply]