On Tue, May 27, 2014 at 10:29 PM, Eric Botcazou <ebotca...@adacore.com> wrote: > This is an old bug in div_and_round_double for ROUND_DIV_EXPR: when the code > detects that it needs to adjust the quotient, it needs to decide whether it > increases or decreases it by 1. This only depends on the expected sign of the > quotient, but the test reads: > > if (*hquo < 0) > > So if the quotient is 0, the code will always bump it, thus yielding 1, even > if the expected quotient is negative. This causes the attached Ada testcase > to fail at -O on all active branches... except for mainline, because of the > correct implementation of the same test in wi::div_round: > > if (wi::neg_p (x, sgn) != wi::neg_p (y, sgn)) > return quotient - 1; > else > return quotient + 1; > > It turns out that div_and_round_double has a predicate quo_neg that implements > the same test as the wide-int one and ought to be used here. > > Tested on x86_64-suse-linux (of course this probably doesn't mean anything on > the mainline, but it was also test with 4.7 and 4.9 compilers) and applied on > the mainline as obvious.
I suppose you also install on branches? Thanks, Richard. > > 2014-05-27 Eric Botcazou <ebotca...@adacore.com> > > * double-int.c (div_and_round_double) <ROUND_DIV_EXPR>: Use the proper > predicate to detect a negative quotient. > > > 2014-05-27 Eric Botcazou <ebotca...@adacore.com> > > * gnat.dg/overflow_fixed.adb: New test. > > > -- > Eric Botcazou
