Woops, forgot to copy the list. On Sat, Dec 12, 2009 at 2:15 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Sat, Dec 12, 2009 at 2:00 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> Roman Kononov <kono...@ftml.net> writes: >>> The bitfromint8() and bitfromint4() are hosed. They produce wrong >>> results when the BIT size is more than 64 and 32 respectively, and the >>> BIT size is not multiple of 8, and the most significant byte of the >>> integer value is not 0x00 or 0xff. >> >> Hm, you're right, it's definitely busted ... >> >>> The patch re-implements the conversion functions. >> >> ... but I don't much care for this patch. It's unreadable, uncommented, >> and doesn't even try to follow Postgres coding conventions. >> >> It looks to me like the actual bug is that the "first fractional byte" >> case ought to shift by destbitsleft - 8 not srcbitsleft - 8. A >> secondary problem (which your patch fails to fix) is that if the >> compiler chooses to implement signed >> as zero-fill rather than >> sign-bit-fill (which it is allowed to do per C99) then we'll get >> wrong, or at least not the desired, results. So I arrive at >> the attached patch. > > I'm not sure this fixes it, although I haven't tested. When we take > the /* store first fractional byte */ branch, destbitsleft is between > 1 and 7 bits greater than srcbitsleft. We then subtract 8 from > destbitsleft, and the comment on the next line now asserts that the > two are equal. That doesn't seem right. > > Also, I thought about the sign extension problem, but aren't we > chopping those bits off anyway on the next line? > > ...Robert >
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