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[Bug math/18956] New: powf inaccuracy
- From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Fri, 11 Sep 2015 19:51:55 +0000
- Subject: [Bug math/18956] New: powf inaccuracy
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=18956
Bug ID: 18956
Summary: powf inaccuracy
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: ---
Even in round-to-nearest mode, powf can have errors beyond the 9ulp maximum
accepted in glibc (seen on x86_64 and mips64):
Failure: Test: pow (0xd.73035p-4, -0x1.47bb8p+8)
Result:
is: 5.22400435890634124322e+24 0x1.148e7600000000000000p+82
should be: 5.22399859429881820899e+24 0x1.148e6200000000000000p+82
difference: 5.76460752303423488000e+18 0x1.40000000000000000000p+62
ulp : 10.0000
max.ulp : 3.0000
Failure: Test: pow_downward (0xd.73035p-4, -0x1.47bb8p+8)
Result:
is: 5.22398418278001062340e+24 0x1.148e3000000000000000p+82
should be: 5.22399801783806590556e+24 0x1.148e6000000000000000p+82
difference: 1.38350580552821637120e+19 0x1.80000000000000000000p+63
ulp : 24.0000
max.ulp : 4.0000
Failure: Test: pow_towardzero (0xd.73035p-4, -0x1.47bb8p+8)
Result:
is: 5.22398360631925831997e+24 0x1.148e2e00000000000000p+82
should be: 5.22399801783806590556e+24 0x1.148e6000000000000000p+82
difference: 1.44115188075855872000e+19 0x1.90000000000000000000p+63
ulp : 25.0000
max.ulp : 8.0000
Failure: Test: pow_upward (0xd.73035p-4, -0x1.47bb8p+8)
Result:
is: 5.22400435890634124323e+24 0x1.148e7600000000000000p+82
should be: 5.22399859429881820899e+24 0x1.148e6200000000000000p+82
difference: 5.76460752303423488000e+18 0x1.40000000000000000000p+62
ulp : 10.0000
max.ulp : 8.0000
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