lanx:$ perl -MDevel::Peek -E'$x+=2**$_ for 0..52;Dump ($x);Dump($x+1)'
SV = IV(0x64c9edf22bb0) at 0x64c9edf22bc0
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 9007199254740991
SV = IV(0x64c9edf838d0) at 0x64c9edf838e0
  REFCNT = 1
  FLAGS = (PADTMP,IOK,pIOK)
  IV = 9007199254740992

##</code><code>##

lanx:$ perl -MDevel::Peek -E'$x+=2**$_ for 0..53;Dump ($x);Dump($x+1);say "*** WTF *** " if $x == $x+1'
SV = PVNV(0x5ea09827d340) at 0x5ea0982abd00
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  IV = 9007199254740991
  NV = 18014398509481984
  PV = 0
SV = NV(0x5ea09830cb18) at 0x5ea09830cb30
  REFCNT = 1
  FLAGS = (PADTMP,NOK,pNOK)
  NV = 18014398509481984
*** WTF ***