Andrew, On Tue, Sep 8, 2015 at 3:22 PM, Andrew Haley <aph@xxxxxxxxxx> wrote: > On 09/08/2015 01:40 PM, Mathieu Malaterre wrote: >> On Tue, Sep 8, 2015 at 2:00 PM, Mathieu Malaterre <malat@xxxxxxxxxx> wrote: >>> FYI, >>> >>> On Tue, Sep 8, 2015 at 12:04 PM, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote: >>> [...] >>>> That's not the only option. You could compile one file with GCC and >>>> all others with Clang and see if you can reproduce it. Repeat for each >>>> file, which will narrow down the file where the problem occurs. Then >>>> you can try splitting that file into smaller pieces, with one function >>>> per file, and repeat the process. That would tell you which function >>>> or functions get miscompiled by GCC. >>> >>> Ok so if I compile eveything with gcc and then only `tcd.c` using >>> clang, then everything works as expected (no symptoms). >>> ref: https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/tcd.c >>> >>> I'll repeat your approach to find the culprit function. >> >> And the culprit function is `opj_tcd_makelayer`: >> >> https://github.com/uclouvain/openjpeg/blob/master/src/lib/openjp2/tcd.c#L218 >> >> Other than the `if (dd / dr >= thresh)` I do not see anything >> obviously suspicious. > > I see floating point, despite your earlier denial. :-) lol. Sorry about that :( > Libopenjpeg has a bad reputation for messing with the floating- > point state. Please make sure the library is not linked with > -ffast-math. > > Beyond that, a few printf()s and "diff" should find the problem. So here what seems to be working for me, replace: if (dd / dr >= thresh) with: double div; /* OPJ_FLOAT64 */ div = dd / dr; if (div >= thresh) However reading the documentation of gcc: https://gcc.gnu.org/onlinedocs/gcc-5.2.0/gcc/Optimize-Options.html#index-ffloat-store-1074 It appears that -ffloat-store is not activated by default (I did check that using also the output of `gcc -Q -v`). So could someone please let me know why `gcc -m32` (no other option!) produce different behavior (=removes excess precision if my understanding is correct) in the two above cases ? Thanks much again for help,
