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http://sourceware.org/bugzilla/show_bug.cgi?id=13881 Bug #: 13881 Summary: powl inaccurate for x86/x86_64 Product: glibc Version: 2.15 Status: NEW Severity: normal Priority: P2 Component: math AssignedTo: unassigned@sourceware.org ReportedBy: jsm28@gcc.gnu.org Classification: Unclassified The powl implementations for x86 and x86_64 work essentially through exp2 (y * log2 (x)). This does not produce accurate results for large outputs; you need about 15 extra bits of precision in the evaluation of y * log2 (x) to do that. As an example, powl (1e4932L, 0.75L) is 4840ulp off from the expected 1e3699L on x86_64. For integer exponents a different algorithm is used; it's still not very accurate, e.g. 45ulp error for powl (10, 4932); that has the same underlying cause as the inaccuracy described for pow in bug 706. -- Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are on the CC list for the bug.
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