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[Bug math/19375] New: powerpc: incorrect results for POWER7 logb with negative subnormals
- From: "adhemerval.zanella at linaro dot org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Thu, 17 Dec 2015 16:29:45 +0000
- Subject: [Bug math/19375] New: powerpc: incorrect results for POWER7 logb with negative subnormals
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=19375
Bug ID: 19375
Summary: powerpc: incorrect results for POWER7 logb with
negative subnormals
Product: glibc
Version: 2.23
Status: NEW
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: adhemerval.zanella at linaro dot org
Target Milestone: ---
The 'math/test-double' and 'math/test-double-finite' are both failing on POWER7
or newer machine with:
testing double (finite-math-only)
Failure: Test: logb (-min_subnorm_value)
Result:
is: -1.0110000000000000e+03 -0x1.f980000000000p+9
should be: -1.0740000000000000e+03 -0x1.0c80000000000p+10
difference: 6.3000000000000000e+01 0x1.f800000000000p+5
ulp : 277076930199552.0000
max.ulp : 0.0000
Failure: Test: logb_downward (-min_subnorm_value)
Result:
is: -1.0110000000000000e+03 -0x1.f980000000000p+9
should be: -1.0740000000000000e+03 -0x1.0c80000000000p+10
difference: 6.3000000000000000e+01 0x1.f800000000000p+5
ulp : 277076930199552.0000
max.ulp : 0.0000
Failure: Test: logb_towardzero (-min_subnorm_value)
Result:
is: -1.0110000000000000e+03 -0x1.f980000000000p+9
should be: -1.0740000000000000e+03 -0x1.0c80000000000p+10
difference: 6.3000000000000000e+01 0x1.f800000000000p+5
ulp : 277076930199552.0000
max.ulp : 0.0000
Failure: Test: logb_upward (-min_subnorm_value)
Result:
is: -1.0110000000000000e+03 -0x1.f980000000000p+9
should be: -1.0740000000000000e+03 -0x1.0c80000000000p+10
difference: 6.3000000000000000e+01 0x1.f800000000000p+5
ulp : 277076930199552.0000
max.ulp : 0.0000
This is due a issue on 'sysdeps/powerpc/power7/fpu/s_logb.c' for handling
subnormal negative numbers (it does not clear the sign bit before issue the
leading 0-bits builtin).
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