From 8724cf43c27922c2a9eb10846bafbe2f3d8f7cef Mon Sep 17 00:00:00 2001
From: rsiddharth <s@ricketyspace.net>
Date: Sun, 29 Sep 2019 19:08:30 -0400
Subject: nserver: Add stats.h

---
 nserver/src/stats.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 nserver/src/stats.h | 33 ++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100644 nserver/src/stats.c
 create mode 100644 nserver/src/stats.h

diff --git a/nserver/src/stats.c b/nserver/src/stats.c
new file mode 100644
index 0000000..68b99cc
--- /dev/null
+++ b/nserver/src/stats.c
@@ -0,0 +1,54 @@
+#include <math.h>
+#include <stats.h>
+#include <stdlib.h>
+#include <dbg.h>
+
+Stats *Stats_recreate(double sum, double sumsq, unsigned long n,
+                      double min, double max)
+{
+    Stats *st  = malloc(sizeof(Stats));
+    check_mem(st);
+
+    st->sum =  sum;
+    st->sumsq = sumsq;
+    st->n  = n;
+    st->min = min;
+    st->max = max;
+
+    return st;
+
+ error:
+    return NULL;
+}
+
+Stats *Stats_create()
+{
+    return Stats_recreate(0.0, 0.0, 0L, 0.0, 0.0);
+}
+
+void Stats_sample(Stats *st, double s)
+{
+    st->sum  += s;
+    st->sumsq += s * s;
+
+    if (st->n == 0) {
+        st->min = s;
+        st->max = s;
+    } else {
+        if (st->min > s)
+            st->min = s;
+        if (st->max < s)
+            st->max = s;
+    }
+
+    st->n += 1;
+}
+
+void Stats_dump(Stats *st)
+{
+    fprintf(stderr,
+            "sum: %f, sumsq: %f, n: %ld, "
+            "min: %f, max: %f, mean: %f, stddev: %f",
+            st->sum, st->sumsq, st->n, st->min, st->max, Stats_mean(st),
+            Stats_stddev(st));
+}
diff --git a/nserver/src/stats.h b/nserver/src/stats.h
new file mode 100644
index 0000000..997a505
--- /dev/null
+++ b/nserver/src/stats.h
@@ -0,0 +1,33 @@
+#ifndef stats_h
+#define stats_h
+#include <math.h>
+
+typedef struct Stats {
+    double sum;
+    double sumsq;
+    unsigned long n;
+    double min;
+    double max;
+} Stats;
+
+Stats *Stats_recreate(double sum, double sumsq, unsigned long n,
+                      double min, double max);
+
+Stats *Stats_create();
+
+void Stats_sample(Stats *st, double s);
+
+void Stats_dump(Stats *st);
+
+static inline double Stats_mean(Stats *st)
+{
+    return st->sum / st->n;
+}
+
+static inline double Stats_stddev(Stats *st)
+{
+    return sqrt((st->sumsq - (st->sum * st->sum / st->n)) /
+                (st->n - 1));
+}
+
+#endif
-- 
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