[Python-Dev] [Python-checkins] cpython (2.7): Issue #10276: test_zlib checks that inputs of 2 GB are handled correctly by (original) (raw)

Ethan Furman ethan at stoneleaf.us
Thu May 5 14:07:04 CEST 2011

Victor Stinner wrote:

Le mercredi 04 mai 2011 à 15:40 -0700, Ethan Furman a écrit :

Victor Stinner wrote:

Le mardi 03 mai 2011 à 16:22 +0200, Nadeem Vawda a écrit :

On Tue, May 3, 2011 at 3:19 PM, victor.stinner <python-checkins at python.org> wrote:

+ intmax = 0x7FFFFFFF + with open(TESTFN, "wb+") as f: + f.seek(self.intmax-4) + f.write("asdf") + f.flush() 0x7FFFFFFF is (2G-1) bytes. For a 2GB buffer, intmax should be 0x80000000. However, if you make this change, crc32() and adler32() raise OverflowErrors (see changeset a0681e7a6ded).

I don't want to check OverflowError: the test is supposed to compute the checksum of a buffer of 0x7FFFFFFF bytes

The comment says 'check that inputs of 2 GB are handled correctly' but the file created is 1 byte short of 2Gb. Is the test wrong, or just wrongly commented? Or am I not understanding? If you write a byte after 2 GB of zeros, the file size is 2 GB+the few bytes. This trick is to create quickly a large file: some OSes support sparse files, zeros are not written on disk. But on Mac OS X and Windows, you really write 2 GB+some bytes.

True, but that's not what's happening -- four bytes are being written at int_max - 4, and int_max is one less that 2GB; hence the resulting file is one less than 2GB.

Ethan

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