fix mmap module (broken seek, 64-bit stuff, overflows) about cpython

[tmick]

[gvanrossum]

Andrew, I'm not sure if you can review patches for Windows, but since it's your module, I'd like you to have a look at this first. Tim should get it next.

[akuchling]

The patches look OK, particularly the fixing of the seek()
method. I'm not sure why various casts are changed from (long) to (int), and wonder if those casts could simply be removed, but that's not a problem.

[tim-one]

Best I can tell, this has already been checked in!
So marking Closed, and assigning back to AMK. Andrew, scream at me if I done wrong here.

[tmick]

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[tmick]

This patch fixes some issues in the mmap module. The changes are:

• The use of HFILE for Win32 is no longer appropriate for Win32/64,
  all of the associated system calls use a pointer length integer, hence HFILE
  is replaced with INT_PTR (a Windows world typedef for this)

• Do proper bounds checking limiting the length of a mmap'd file to [0,
  INT_MAX] (see _GetMapSize()). INT_MAX is chosen because this is the current
  restriction on the length of Python objects and a mmap'd file larger than
  this cannot be used effectively anyway. For instance a mmap'd file longer
  than INT_MAX cannot be sliced beyond INT_MAX, or indexed, etc. Until the
  limit on the size of Python objects increases then there is little use in
  having larger mmap'd files.

• The mmap_seek is fairly significantly broken (seeking from the current
  position or from the end are both borken, IIRC). This patch fixes that,
  checks for possible out of range seek values, and extends test_mmap.py to
  test this stuff.

• Use a C int for variables associated with the length field of Python
  objects, this is what it is and the distinction matters on Linux64, for
  example.

• Use safe number literals. (some unsigned)0xFFFFFFFF -> (some unsigned)-1
  The former does not give the intended result iff 'some unsigned' is >
  32-bits.

[tmick]

Some of the casts were changed from (long) to (int) because 'int' was the size being returned (for example in the length value to PyString_FromStringAndSize, or the mmap find method is specified to return an int and not a long, note that sizeof(int) != sizeof(long) on Linux64.

Note that this has already been checked in:
http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/python/dist/src/Modules/mmapmodule.c.diff?cvsroot=python&r1=2.12&r2=2.13&f=H

...and in the actual checkin the first cast to (int) was dropped anyway :). Maybe you did that yourself, Andrew.