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[Bug math/16789] New: clog / clog10 sign of zero result incorrect in round-downward mode


https://sourceware.org/bugzilla/show_bug.cgi?id=16789

            Bug ID: 16789
           Summary: clog / clog10 sign of zero result incorrect in
                    round-downward mode
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org

In round-downward mode, clog and clog10 produce results with a real part -0
when it should be +0.  This includes both cases with an exact 0 result (where
+0 is the natural analogy with log) and cases where the mathematical result is
positive but should round to 0.  For example, for double on x86_64:

Failure: Test: Real part of: clog_downward (0x1p+0 + +0 i)
Result:
 is:         -0.00000000000000000000e+00  -0x0.00000000000000000000p+0
 should be:   0.00000000000000000000e+00   0x0.00000000000000000000p+0

and

Failure: Test: Real part of: clog_downward (0x1p+0 + 0x4p-1076 i)
Result:
 is:         -0.00000000000000000000e+00  -0x0.00000000000000000000p+0
 should be:   0.00000000000000000000e+00   0x0.00000000000000000000p+0

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