[Bug math/18952] New: [ldbl-128/ldbl-128ibm] lgammal spurious "invalid", incorrect signgam

["jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18952

            Bug ID: 18952
           Summary: [ldbl-128/ldbl-128ibm] lgammal spurious "invalid",
                    incorrect signgam
           Product: glibc
           Version: 2.22
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org
  Target Milestone: ---

The ldbl-128 / ldbl-128ibm implementation of lgammal converts (the floor of
minus) non-integer negative arguments to int to determine the value of signgam.
 When those values are outside the range of int, this produces spurious
"invalid" exceptions and incorrect values of signgam.  E.g., for mips64:

Failure: lgamma (-0x1.000000008p+32): Exception "Invalid operation" set
Failure: Test: lgamma (-0x1.000000008p+32) extra output 1
Result:
 is:         1
 should be:  -1
Failure: lgamma (-0x1.000000018p+32): Exception "Invalid operation" set

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