On Mon, Jan 21, 2019 at 6:03 PM Joseph Myers <jos...@codesourcery.com> wrote: > > On Mon, 21 Jan 2019, H.J. Lu wrote: > > > The testcase at > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88931 > > > > with -frounding-math. __floattisf and __floattidf from libgcc2.c give > > the wrong results for FE_UPWARD and FE_TOWARDZERO. > > I suggest writing a test that looks something like > gcc.dg/torture/fp-int-convert-float128-timode-3.c - one that verifies the > conversion of a single value, in a single rounding mode (four such tests > if you want to verify conversions for each of SFmode and DFmode, in each > of two rounding modes). Of course that test wouldn't have any of the dg-* > related to __float128, because this isn't a float128 issue. Given such a > test that uses volatile as appropriate and just does and checks one > conversion, we can be confident we have a real issue (not something about > code movement). > > If such a test shows a bug, it will be somewhere in the libgcc2.c code, > with the appropriate fix being in that code. Since that code has lots of > conditionals in it, it would help to identify exactly which cases in that > code are used; that is, which of the > > #if FSSIZE >= W_TYPE_SIZE > > #elif (LIBGCC2_HAS_DF_MODE && F_MODE_OK (__LIBGCC_DF_MANT_DIG__)) \ > || (LIBGCC2_HAS_XF_MODE && F_MODE_OK (__LIBGCC_XF_MANT_DIG__)) \ > || (LIBGCC2_HAS_TF_MODE && F_MODE_OK (__LIBGCC_TF_MANT_DIG__)) > > or > > #else > > cases is being used (and, in the second case, what FSIZE and FTYPE are). > The bug could either be in the code in the selected case, or in the logic > that selects which case to use. > > Based on code inspection, it's possible the issue is with > > /* No leading bits means u == minimum. */ > if (count == 0) > return -(Wtype_MAXp1_F * (Wtype_MAXp1_F / 2)); > > in the third case (where actually count == 0 only means the high part is > minimum). In which case something like > > return Wtype_MAXp1_F * (FSTYPE) (hi | ((UWtype) u != 0)); > > for the (count == 0) case would address the problem.
Yes, this works. -- H.J.
