Re: BUG #13442: ISBN doesn't always roundtrip with text

bz@mailinator.com writes:
> I have a table containing ISBNs stored as the isbn type provided by the isn
> extension. In certain cases an ISBN in ISBN10 form is considered unequal to
> the same ISBN in ISBN13 form.

I poked at this a little bit.  I think the issue may be that this bit
at line 832 in isn.c:

        case ISBN:
            memcpy(buf, "978", 3);

supposes that all ISBNs should have prefix 978, whereas your example is
using prefix 979, which seems to be also valid according to code a few
lines above.  I don't know enough about the whole ISBN/EAN mess to
understand what this should be doing instead, though.

            regards, tom lane