Hello MRAB, yes, like that :-)
Thanks, Karsten On Thu, Nov 14, 2019 at 09:11:37PM +0000, MRAB wrote: > Date: Thu, 14 Nov 2019 21:11:37 +0000 > From: MRAB <pyt...@mrabarnett.plus.com> > To: python-list@python.org > Subject: Re: py2 vs py3: zlib.adler32/crc32 > User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 > Thunderbird/60.9.1 > > On 2019-11-14 19:22, Karsten Hilbert wrote: > > Hi all, > > > > I am unsure how to solve: I use adler32/crc32 to generate integer values > > from data > > for setting up an advisory lock in PostgreSQL. > > > > The PG function pg_try_advisory_lock() > > > > > > https://www.postgresql.org/docs/12/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS > > > > takes two PG ints which are defined as: > > > > integer 4 bytes typical choice for integer > > -2147483648 to +2147483647 > > > > Now, in Py > 2.5 zlib.adler32/crc32 will return suitable integers. > > > > However, in Py3 the return range has been changed to > > > > The return value is unsigned and in the range [0, 2**32-1] regardless > > of platform. > > > > which will overflow the PostgreSQL function. > > > > Is there a way to convert/modify/shift the py3 value such that it shows the > > same representation as the py2 value ? What I am looking for is: > > > > v2 = py2.zlib.adler32(data) > > v3 = some_magic(py3.zlib.adler32(data)) > > if v2 == v3: > > print('same') > > > > I am sure there's something obvious with struct/<</& and > > such like which I am overlooking. > > > > Note that I can't simply do > > > > v2 = py2.zlib.adler32(data) & 0xffffffff > > > > because that can overflow the PostgreSQL integer. I think I need > > the reverse, in a sense, but I am too dense, ATM. > > > Unsigned 32-bit to signed 32-bit: > > unsigned - (unsigned & 0x80000000) * 2 > > Signed 32-bit to unsigned 32-bit: > > signed & 0xFFFFFFFF > -- > https://mail.python.org/mailman/listinfo/python-list -- GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B -- https://mail.python.org/mailman/listinfo/python-list
