I don't mean to put pressure - I just leave this here for anyone.

both of these fail with an infinite loop printing i=10 on linux fedora 30, perl 5.28.2. 10 and 15 are the min numbers to do this.

use bignum (p=>1);

for(my $i = 1;$i->blt(15);$i->binc()){
    print "i=$i\n";
    
}
[download]

for(my $i = 1;$i<=10;$i++){
    print "i=$i\n";
}
[download]

this shows to me that it is not the loop or the overloaded increment but that when p=>1 it thinks that it's adding that value divided by 10 or something

my $i = 10;
        print "1 i=$i\n";
$i++;
        print "2 i=$i\n";
$i = $i + 1;
        print "3 i=$i\n";
$i = $i + 2;
        print "4 i=$i\n";
$i = $i + 3;
        print "5 i=$i\n";
$i = $i + 4;
        print "6 i=$i\n";
$i = $i + 5;
        print "7 i=$i\n";
$i = $i + 6 ;
        print "8 i=$i\n";
[download]

1 i=10
2 i=10
3 i=10
4 i=10
5 i=10
6 i=10
7 i=20
8 i=30
[download]

I have filed a bug to bigint

The maintainer of bigint replied to filing a bug:

Here is your problem: p=>1 specifies a precision of 1. See these for 
comparisation:

  $ perl -Mbignum=p,1 -wle '$i = 1; print $i + 123456788,"\n"'
  123456790

  $ perl -Mbignum=p,2 -wle '$i = 1; print $i + 123456788,"\n"'
  123456800

  $ perl -Mbignum=p,5 -wle '$i = 1; print $i + 123456788,"\n"'
  123500000

Looks to me it works as designed.

Here is the same with different accuracy values:

  $ perl -Mbignum=a,1 -wle '$i = 1; print $i + 123456788,"\n"'
  100000000

  $ perl -Mbignum=a,2 -wle '$i = 1; print $i + 123456788,"\n"'
  120000000

  $ perl -Mbignum=a,3 -wle '$i = 1; print $i + 123456788,"\n"'
  123000000

and with negative values of p:

  $ perl -Mbignum=p,-3 -wle '$i = 1; print $i + 123456789.1,"\n"'
  123456790.100

  $ perl -Mbignum=p,-6 -wle '$i = 1; print $i + 123456789.1,"\n"'
  123456790.100000

Best regards,

Tels
[download]

I am thinking to reply with maybe bignum should be put under the ACME tree? but holding back thinking I am too extreme. I still can't digest that forloop behaviour. Fair enough it's a design choice but the unawary, common-sense Perl user is in for a big surprise when trying to ... increase precision.