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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 |
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