Re: Largest integer in 64-bit perl

[pfaut]

Perl may internally keep your numbers as floating point values unless you tell it not to. Add use integer; at the top of your program and see what happens.

If you want to print integer values, use %d, not %f in your print format.

A hex value of all 'F's represents a negative value (2's complement notation). I altered your max value to be the largest 64 bit positive number.

use integer;

my $MAXQUAD = 9223372036854775807;   # equals 0x7fffffffffffffff

for (my $i = 0; $i <= $MAXQUAD; $i++)
{
  printf("\n %d", $i);
}
exit;

[harangzsolt33]

Interestingly, the "use integer" line did absolutely nothing for me on 32-bit Windows XP TinyPerl 5.8. I tried to run it on Linux with 64-bit Perl 5.36, and to my surprise, it didn't even run! :-O It produced no error message and no output at all. The program does have a for loop in it, but it looked like it didn't even start the loop. I don't understand... Here's the program again:

#!/usr/bin/perl

use strict;
use warnings;
use integer;

$| = 1;

my $MAXQUAD = 18446744073709551615;

for (my $i = 9007199254740000; $i <= $MAXQUAD; $i++)
{
  printf("\n %.0f   %d", $i, $i);
}

So, anyway, I did notice that if I remove the "use integer" line, then the program runs. In fact, if I started the loop at, let's say, 4611686018420000000, then it will keep counting on the 64-bit Perl in Linux. Interesting!

However, when I stop the program by pressing CTRL+C, I notice something else. When printing the number $i as float, it sort of loses precision, but when printing it as %d number, it prints it precisely. In TinyPerl, I had the opposite experience with this where %f printed more precise values than %d. This is so weird... :P

 4611686018420022272  4611686018420022338
 4611686018420022272  4611686018420022339
 4611686018420022272  4611686018420022340
 4611686018420022272  4611686018420022341
 4611686018420022272  4611686018420022342
 4611686018420022272  4611686018420022343
 4611686018420022272  4611686018420022344
 4611686018420022272  4611686018420022345
 4611686018420022272  4611686018420022346
 4611686018420022272  4611686018420022347
 4611686018420022272  4611686018420022348
 4611686018420022272  4611686018420022349
 4611686018420022272  4611686018420022350

[pfaut]

Try printing $MAXQUAD. I bet you get '-1'. That's why your code looks like it doesn't run.

Update: I tried this and it prints the set value. However, I wonder if perl is treating it as a signed value when comparing it to $i because the loop never executes.