On Mon, Jan 25, 2016 at 2:34 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Perhaps we can fix this by rewriting as > > float8 numerator = 1.0 - cos(x * RADIANS_PER_DEGREE); > return 1.0 - (numerator / one_minus_cos_60) / 2.0; > > cockatiel's compiler does recognize -fexcess-precision=standard, and > my understanding of that is that the result put into "numerator" will > be rounded to double width, so that it should then match > "one_minus_cos_60". > > Another idea would be to change the cache variable to just "cos_60" and > write "(1.0 - cos_60)" in the denominator --- but then we'd just be hoping > that the compiler does both subtractions the same way, which doesn't seem > necessarily guaranteed. Worse, I believe the 8087 has an FCOS instruction > which might deliver a wider-than-double result, so that maybe the problem > is not so much with the subtraction as with when rounding of the cos() > result happens. The code I show above seems more likely to match the > way one_minus_cos_60 is computed.
(Sorry for showing up after the storm) The fix is working correctly, using gcc's i686-pc-cygwin on cygwin32 the regression does not show up anymore after 0034757. -- Michael -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
