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j0_downward failures on i686 with gcc 6.


Joseph,

On i686 using GCC 6.0 I see some additional +1 ULP changes in j0.

Does this seem like normal compiler-induced changed in precision?
Like selecting slightly different instructions that produce a slightly
different result? Might it be OK to adjust this up by an ULP to avoid
the test failure or do we need to know exactly why this changed?

The machine in question is an Intel E5540, so nothing odd there.

testing float (without inline functions)
Failure: Test: j0_downward (0xap+0)
Result:
 is:         -2.45935813e-01  -0x1.f7ad32p-3
 should be:  -2.45935768e-01  -0x1.f7ad2cp-3
 difference:  4.47034835e-08   0x1.800000p-25
 ulp       :  3.0000
 max.ulp   :  2.0000
Maximal error of `j0_downward'
 is      : 3 ulp
 accepted: 2 ulp
Test suite completed:
  58942 test cases plus 53146 tests for exception flags and
    53146 tests for errno executed.
  2 errors occurred.

testing float (finite-math-only)
Failure: Test: j0_downward (0xap+0)
Result:
 is:         -2.45935813e-01  -0x1.f7ad32p-3
 should be:  -2.45935768e-01  -0x1.f7ad2cp-3
 difference:  4.47034835e-08   0x1.800000p-25
 ulp       :  3.0000
 max.ulp   :  2.0000
Maximal error of `j0_downward'
 is      : 3 ulp
 accepted: 2 ulp
Test suite completed:
  46382 test cases plus 41098 tests for exception flags and
    0 tests for errno executed.
  2 errors occurred.

testing float (inline functions)
Failure: Test: j0_downward (0xap+0)
Result:
 is:         -2.45935813e-01  -0x1.f7ad32p-3
 should be:  -2.45935768e-01  -0x1.f7ad2cp-3
 difference:  4.47034835e-08   0x1.800000p-25
 ulp       :  3.0000
 max.ulp   :  2.0000
Maximal error of `j0_downward'
 is      : 3 ulp
 accepted: 2 ulp
Test suite completed:
  58518 test cases plus 0 tests for exception flags and
    0 tests for errno executed.
  2 errors occurred.

Cheers,
Carlos.


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