if numbers do go over 2 GB, Perl automatically upgrades you to floats

If perl has been built with use64bitint and without uselongdouble, the "upgrade" can happen before the 2GB limit is reached ... which is definitely not what you want (as it means you've lost precision): 
$ perl -MDevel::Peek -le 'Dump(17 + (2 ** 56))'
SV = NV(0x10450940) at 0x10410fd0
  REFCNT = 1
  FLAGS = (PADBUSY,PADTMP,NOK,READONLY,pNOK)
  NV = 7.2057594037928e+16

[download]
In this instance, the workaround is to 'use integer': 
$ perl -Minteger -MDevel::Peek -le 'Dump(17 + (2 ** 56))'
SV = IV(0x10429358) at 0x10410fdc
  REFCNT = 1
  FLAGS = (PADBUSY,PADTMP,IOK,READONLY,pIOK)
  IV = 72057594037927953

[download]
Just a little trap for the unwary.

Cheers,
Rob

Update: Ooops - where *I* wrote 2GB above, I should have written "64-bit". And my point is unrelated to tilly's, anyway ....

In reply to Re^8: use64bitint in building Perl by syphilis
in thread use64bitint in building Perl by cmac

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