http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47146
--- Comment #3 from Pierre Innocent <babelart at yahoo dot com> 2011-01-03 17:12:05 UTC --- Dear kargl: Sorry, I was not specific enough. It is the integer conversion that seem to be wrong,for example the following two lines: fprintf( stdout, "Float 100.0 * 0.3894949=%d\n", 100.0 * elapsed ); fprintf( stdout, "Float 100 * 0.3894949=%d\n", 100 * elapsed ); both produce the value '-536870912'. I also downloaded the C99 integer to float conversion test code; and they generated two many failures. I also believe the compiler should round resulting integer values when stripping decimals off. Regards, Pierre Innocent --- On Sat, 1/1/11, kargl at gcc dot gnu.org <gcc-bugzi...@gcc.gnu.org> wrote: > From: kargl at gcc dot gnu.org <gcc-bugzi...@gcc.gnu.org> > Subject: [Bug c/47146] Floating point to integer conversions > To: babel...@yahoo.com > Received: Saturday, January 1, 2011, 4:15 PM > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47146 > > kargl at gcc dot gnu.org changed: > > What > |Removed > |Added > ---------------------------------------------------------------------------- > > Status|UNCONFIRMED > |RESOLVED > > CC| > > |kargl at gcc dot gnu.org > Resolution| > > |INVALID > > --- Comment #2 from kargl at gcc dot gnu.org 2011-01-01 > 21:15:30 UTC --- > (In reply to comment #0) > > #include <stdio.h> > > #include <stdlib.h> > > > > > //----------------------------------------------------------------------------- > > int32_t main(int argc, char **argv) > > > //----------------------------------------------------------------------------- > > { > > float elapsed = 0.3894949; > > > > fprintf( stdout, "Float > 0.3894949=%f\n", elapsed ); > > fprintf( stdout, "Float > 0.3894949 * 100.0=%f\n", elapsed * 100.0 ); > > fprintf( stdout, "Integer Cast > 0.3894949 * 100.0=%d\n", (int32_t) (elapsed > > * 100.0) ); > > > > If you change all your floating point constants to include > a f > suffix (e.g., 100.0f, 0.3894949f, etc), then you get > > laptop:kargl[149] cc -o z a.c -ffloat-store && ./z > Float 0.3894949=0.389495 > Float 0.3894949 * 100.0=38.949490 > Integer Cast 0.3894949 * 100.0=38 > Float=38.949490 > Integer=38 > ------------------------------ > Float 0.39=0.390000 > Float 0.39 * 100.0=39.000000 > Integer Cast 0.39 * 100.0=39 > Float=39.000000 > Integer=39 > > which looks like the desired output. As Jonathan > mentions, you > have several intermediate results that are double not > float. > Add the fact that 0.39 is not exactly representable, which > your output of "Float 0.39 * 100.0=38.999999" clearly > shows, > you've miss interpreted your results. > > -- > Configure bugmail: http://gcc.gnu.org/bugzilla/userprefs.cgi?tab=email > ------- You are receiving this mail because: ------- > You reported the bug. >
