[Bug math/21280] New: [powerpc] logbl for POWER7 return incorrect results

[tuliom at linux dot vnet.ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=21280

            Bug ID: 21280
           Summary: [powerpc] logbl for POWER7 return incorrect results
           Product: glibc
           Version: 2.25
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: tuliom at linux dot vnet.ibm.com
  Target Milestone: ---

The errors affect negative subnormals and values near powers of 2.

testing long double (without inline functions)
Failure: Test: logb (-min_subnorm_value)
Result:
 is:         -1.01100000000000000000000000000000e+03 
-0x1.f98000000000000000000000000p+9
 should be:  -1.07400000000000000000000000000000e+03 
-0x1.0c8000000000000000000000000p+10
 difference:  6.30000000000000000000000000000000e+01  
0x1.f80000000000000000000000000p+5
 ulp       :  2495687119199326634196634435584.0000
 max.ulp   :  0.0000
Failure: Test: logb (0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb (-0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_downward (-min_subnorm_value)
Result:
 is:         -1.01100000000000000000000000000000e+03 
-0x1.f98000000000000000000000000p+9
 should be:  -1.07400000000000000000000000000000e+03 
-0x1.0c8000000000000000000000000p+10
 difference:  6.30000000000000000000000000000000e+01  
0x1.f80000000000000000000000000p+5
 ulp       :  2495687119199326634196634435584.0000
 max.ulp   :  0.0000
Failure: Test: logb_downward (0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_downward (-0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_towardzero (-min_subnorm_value)
Result:
 is:         -1.01100000000000000000000000000000e+03 
-0x1.f98000000000000000000000000p+9
 should be:  -1.07400000000000000000000000000000e+03 
-0x1.0c8000000000000000000000000p+10
 difference:  6.30000000000000000000000000000000e+01  
0x1.f80000000000000000000000000p+5
 ulp       :  2495687119199326634196634435584.0000
 max.ulp   :  0.0000
Failure: Test: logb_towardzero (0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_towardzero (-0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_upward (-min_subnorm_value)
Result:
 is:         -1.01100000000000000000000000000000e+03 
-0x1.f98000000000000000000000000p+9
 should be:  -1.07400000000000000000000000000000e+03 
-0x1.0c8000000000000000000000000p+10
 difference:  6.30000000000000000000000000000000e+01  
0x1.f80000000000000000000000000p+5
 ulp       :  2495687119199326634196634435584.0000
 max.ulp   :  0.0000
Failure: Test: logb_upward (0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000
Failure: Test: logb_upward (-0x1.ffffffffffffffp1)
Result:
 is:          2.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+1
 should be:   1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 difference:  1.00000000000000000000000000000000e+00  
0x1.000000000000000000000000000p+0
 ulp       :  40564819207303340847894502572032.0000
 max.ulp   :  0.0000

Test suite completed:
  120 test cases plus 116 tests for exception flags and
    116 tests for errno executed.
  12 errors occurred.

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