Fix failure to zero-pad the result of bitshiftright().
If the bitstring length is not a multiple of 8, we'd shift the
rightmost bits into the pad space, which must be zeroes --- bit_cmp,
for one, depends on that. This'd lead to the result failing to
compare equal to what it should compare equal to, as reported in
bug #16013 from Daryl Waycott.
This is, if memory serves, not the first such bug in the bitstring
functions. In hopes of making it the last one, do a bit more work
than minimally necessary to fix the bug:
* Add assertion checks to bit_out() and varbit_out() to complain if
they are given incorrectly-padded input. This will improve the
odds that manual testing of any new patch finds problems.
* Encapsulate the padding-related logic in macros to make it
easier to use.
Also, remove unnecessary padding logic from bit_or() and bitxor().
Somebody had already noted that we need not re-pad the result of
bit_and() since the inputs are required to be the same length,
but failed to extrapolate that to the other two.
Also, move a comment block that once was near the head of varbit.c
(but people kept putting other stuff in front of it), to put it in
the header block.
Note for the release notes: if anyone has inconsistent data as a
result of saving the output of bitshiftright() in a table, it's
possible to fix it with something like
UPDATE mytab SET bitcol = ~(~bitcol) WHERE bitcol != ~(~bitcol);
This has been broken since day one, so back-patch to all supported
branches.
Discussion: https://postgr.es/m/16013-c2765b6996aacae9@postgresql.org
Branch
------
REL9_6_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/6ddd164aaa344d2e9a1e3e62f69b6dcdfd329501
Modified Files
--------------
src/backend/utils/adt/varbit.c | 165 ++++++++++++++++++--------------------
src/include/utils/varbit.h | 5 ++
src/test/regress/expected/bit.out | 66 +++++++++++++++
src/test/regress/sql/bit.sql | 7 +-
4 files changed, 154 insertions(+), 89 deletions(-)
