[Bug libgcc/69233] New: fixtfti returns bad value for TI overflow

["munroesj at us dot ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69233

            Bug ID: 69233
           Summary: fixtfti returns bad value for TI overflow
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
          Assignee: unassigned at gcc dot gnu.org
          Reporter: munroesj at us dot ibm.com
  Target Milestone: ---

When converting IBM long double to __int128, large values that overflow are not
returning the expected values.

To be consistent with double to long conversions the conversion to __int128
should return saturated values and set Invalid Integer Convert (VXCVI)
floating-point exception.

For a large positive long double ( > 170141183460469231731687303715884105727.L)
I would expect 0x7fffffffffffffffffffffffffffffff (largest positive __int128)
but __fixtfti returns 0xffffffffffffffffffffffffffffffff

For large negative long double I would expect
0x80000000000000000000000000000000 (largest negative __int128) but __fixtfti
returns 000000000000000000000000000000000000001 or other small positive values.