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
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