I see, so the get/set_bit functions act on bits within individual bytes, not as a bit stream. Some other languages will act directly on the bits, rather than iterating over bytes.
A good example of this is in pure C when setting a bit, it is easy to do programmatically with shifting. This is how I've performed these operations in the past, specifically when looping over bits.
Eg.
unsigned int x = 13;
unsigned int i = 0;
i |= 1 << x;
This will set the bit in the bytes relative to the right-most position. In this case, it would return an integer with a value of 32, having bytes with the hex representation 0x00002000 (when using printf, MSB).
Now that I understand the implementation reasoning, I also understand that this will probably not change. If there are some bit functions implemented with the BYTEA type similar to the C above, however, I would definitely expect it to perform the same way.
Francisco Olarte <folarte@peoplecall.com> writes:
> On Thu, Apr 30, 2020 at 9:47 AM PG Bug reporting form
> <noreply@postgresql.org> wrote:
>> set_bit function changes the right-most bit of the byte, but with
>> little-endian byte order. This is confusing to any use case where setting a
>> bit in a BYTEA in a specific position. To iterate through the bits within
>> the BYTEA, one must have nested loops which set bits within byte boundaries.
> I think this is a display expectations issue, when using addresses it
> seems it is changing the least significant bit in the first byte and
> the second byte ( in C-speak it is setting bit n%8 byte n/8 ),
Yeah, the documentation is quite clear about this:
Functions get_byte and set_byte number the first byte of a binary
string as byte 0. Functions get_bit and set_bit number bits from the
right within each byte; for example bit 0 is the least significant bit
of the first byte, and bit 15 is the most significant bit of the
second byte.
so we're not likely to change it.
You might consider using type "bit" instead of bytea, since the bit
display order is more closely tied to how set_bit() numbers the bits.
Another option is to write your own functions that number the bits
however you want.
regards, tom lane
