Date: Fri, 14 Apr 2017 15:31:04 +0000 (UTC) From: Andriy Gapon <avg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r316853 - head/cddl/contrib/opensolaris/lib/libdtrace/common Message-ID: <201704141531.v3EFV4EZ093447@repo.freebsd.org>
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Author: avg Date: Fri Apr 14 15:31:04 2017 New Revision: 316853 URL: https://svnweb.freebsd.org/changeset/base/316853 Log: dtrace: fix normalization of stddev aggregation To be upstreamed. Discussed with: Bryan Cantrill <bryancantrill@gmail.com> MFC after: 2 weeks Sponsored by: Panzura Modified: head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c Modified: head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c ============================================================================== --- head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c Fri Apr 14 15:22:00 2017 (r316852) +++ head/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c Fri Apr 14 15:31:04 2017 (r316853) @@ -389,8 +389,10 @@ dt_stddev(uint64_t *data, uint64_t norma * The standard approximation for standard deviation is * sqrt(average(x**2) - average(x)**2), i.e. the square root * of the average of the squares minus the square of the average. + * When normalizing, we should divide the sum of x**2 by normal**2. */ dt_divide_128(data + 2, normal, avg_of_squares); + dt_divide_128(avg_of_squares, normal, avg_of_squares); dt_divide_128(avg_of_squares, data[0], avg_of_squares); norm_avg = (int64_t)data[1] / (int64_t)normal / (int64_t)data[0];
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