https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106831
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> --- BTW, I admit I don't know much about decimal{32,64,128}, but https://en.wikipedia.org/wiki/Decimal32_floating-point_format says: Because the significand is not normalized (there is no implicit leading "1"), most values with less than 7 significant digits have multiple possible representations; 1 × 10^2=0.1 × 10^3=0.01 × 10^4, etc. Zero has 192 possible representations (384 when both signed zeros are included). So, I think singleton_p should just always return false for DECIMAL_FLOAT_TYPE_P (at least for now).