>perl -e"printf qq{%.f\n}, 2**53+$_ for +1,0,-1"
9007199254740992
9007199254740992
9007199254740991

>perl -e"printf qq{%.f\n}, -2**53+$_ for +1,0,-1"
-9007199254740991
-9007199254740992
-9007199254740992