why zip64_limit defined as 1<<31 -1?

[jesse]

On Jan 29, 2015 9:27 AM, "Ian Kelly" <ian.g.kelly at gmail.com> wrote:
>
> On Wed, Jan 28, 2015 at 2:36 PM, Chris Angelico <rosuav at gmail.com> wrote:
> > On Thu, Jan 29, 2015 at 5:53 AM, jesse <chat2jesse at gmail.com> wrote:
> >> should not it be 1<<32 -1(4g)?
> >>
> >> normal zip archive format should be able to support 4g file.
> >>
> >> thanks
> >
> > 1<<31-1 is the limit for a signed 32-bit integer. You'd have to look
> > into the details of the zip file format to see whether that's the
> > official limit or not; it might simply be that some (un)archivers have
> > problems with >2GB files, even if the official stance is that it's
> > unsigned.
>
> The bug in which zip64 support was added indicates that the value was
> indeed chosen as the limit of a signed 32-bit integer:
>
> http://bugs.python.org/issue1446489

ok,  then why signed 32-bit integer instead of unsigned 32 integer? any
technical limitation reason? the chosen 2G boundary does not conform to zip
standard specification.

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