From 34ea8c75e6ab2f59cb16a046c1c008db333b1613 Mon Sep 17 00:00:00 2001 From: avg Date: Wed, 24 May 2017 11:11:13 +0000 Subject: [PATCH] MFC r316853: dtrace: fix normalization of stddev aggregation Sponsored by: Panzura git-svn-id: svn://svn.freebsd.org/base/stable/10@318784 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f --- cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c index 04c022b7a..98dc29a84 100644 --- a/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c +++ b/cddl/contrib/opensolaris/lib/libdtrace/common/dt_consume.c @@ -389,8 +389,10 @@ dt_stddev(uint64_t *data, uint64_t normal) * 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]; -- 2.45.0