https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87128
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
1e23 is outside the range where all integers can be represented exactly by a
64-bit IEEE double, and the calculation is imprecise when using i387 floating
point registers.
The expected answer is given when using:
-ffloat-store
or when using:
-msse -mfpmath=sse -fexcess-precision=standard
