From 39077d366e960a11eb30d89918c24c383352e04a Mon Sep 17 00:00:00 2001
From: Florian Forster <octo@collectd.org>
Date: Fri, 1 Jun 2012 14:23:58 +0200
Subject: [PATCH] src/common.[ch]: Add rate_to_value().

---
 src/common.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/common.h | 17 ++++++++++
 2 files changed, 112 insertions(+), 1 deletion(-)

diff --git a/src/common.c b/src/common.c
index 459c7024..4ca58d55 100644
--- a/src/common.c
+++ b/src/common.c
@@ -1230,7 +1230,101 @@ counter_t counter_diff (counter_t old_value, counter_t new_value)
 	}
 
 	return (diff);
-} /* counter_t counter_to_gauge */
+} /* counter_t counter_diff */
+
+int rate_to_value (value_t *ret_value, gauge_t rate, /* {{{ */
+		rate_to_value_state_t *state,
+		int ds_type, cdtime_t t)
+{
+	derive_t delta_gauge;
+	cdtime_t delta_t;
+
+	if (ds_type == DS_TYPE_GAUGE)
+	{
+		state->last_value.gauge = rate;
+		state->last_time = t;
+
+		*ret_value = state->last_value;
+		return (0);
+	}
+
+	/* Counter and absolute can't handle negative rates. Reset "last time"
+	 * to zero, so that the next valid rate will re-initialize the
+	 * structure. */
+	if ((rate < 0.0)
+			&& ((ds_type == DS_TYPE_COUNTER)
+				|| (ds_type == DS_TYPE_ABSOLUTE)))
+	{
+		memset (state, 0, sizeof (*state));
+		return (EINVAL);
+	}
+
+	/* Another invalid state: The time is not increasing. */
+	if (t <= state->last_time)
+	{
+		memset (state, 0, sizeof (*state));
+		return (EINVAL);
+	}
+
+	delta_t = t - state->last_time;
+	delta_gauge = (rate * CDTIME_T_TO_DOUBLE (delta_t)) + state->residual;
+
+	/* Previous value is invalid. */
+	if (state->last_time == 0) /* {{{ */
+	{
+		if (ds_type == DS_TYPE_DERIVE)
+		{
+			state->last_value.derive = (derive_t) rate;
+			state->residual = rate - ((gauge_t) state->last_value.derive);
+		}
+		else if (ds_type == DS_TYPE_COUNTER)
+		{
+			state->last_value.counter = (counter_t) rate;
+			state->residual = rate - ((gauge_t) state->last_value.counter);
+		}
+		else if (ds_type == DS_TYPE_ABSOLUTE)
+		{
+			state->last_value.absolute = (absolute_t) rate;
+			state->residual = rate - ((gauge_t) state->last_value.absolute);
+		}
+		else
+		{
+			assert (23 == 42);
+		}
+
+		state->last_time = t;
+		return (EAGAIN);
+	} /* }}} */
+
+	if (ds_type == DS_TYPE_DERIVE)
+	{
+		derive_t delta_derive = (derive_t) delta_gauge;
+
+		state->last_value.derive += delta_derive;
+		state->residual = delta_gauge - ((gauge_t) delta_derive);
+	}
+	else if (ds_type == DS_TYPE_COUNTER)
+	{
+		counter_t delta_counter = (counter_t) delta_gauge;
+
+		state->last_value.counter += delta_counter;
+		state->residual = delta_gauge - ((gauge_t) delta_counter);
+	}
+	else if (ds_type == DS_TYPE_ABSOLUTE)
+	{
+		absolute_t delta_absolute = (absolute_t) delta_gauge;
+
+		state->last_value.absolute = delta_absolute;
+		state->residual = delta_gauge - ((gauge_t) delta_absolute);
+	}
+	else
+	{
+		assert (23 == 42);
+	}
+
+	*ret_value = state->last_value;
+	return (0);
+} /* }}} value_t rate_to_value */
 
 int service_name_to_port_number (const char *service_name)
 {
diff --git a/src/common.h b/src/common.h
index 6b11b538..8a7d9865 100644
--- a/src/common.h
+++ b/src/common.h
@@ -47,6 +47,14 @@
 		|| (strcasecmp ("no", (s)) == 0) \
 		|| (strcasecmp ("off", (s)) == 0))
 
+struct rate_to_value_state_s
+{
+  value_t last_value;
+  cdtime_t last_time;
+  gauge_t residual;
+};
+typedef struct rate_to_value_state_s rate_to_value_state_t;
+
 char *sstrncpy (char *dest, const char *src, size_t n);
 int ssnprintf (char *dest, size_t n, const char *format, ...);
 char *sstrdup(const char *s);
@@ -292,6 +300,15 @@ int read_file_contents (const char *filename, char *buf, int bufsize);
 
 counter_t counter_diff (counter_t old_value, counter_t new_value);
 
+/* Convert a rate back to a value_t. When converting to a derive_t, counter_t
+ * or absoltue_t, take fractional residuals into account. This is important
+ * when scaling counters, for example.
+ * Returns zero on success. Returns EAGAIN when called for the first time; in
+ * this case the value_t is invalid and the next call should succeed. Other
+ * return values indicate an error. */
+int rate_to_value (value_t *ret_value, gauge_t rate,
+		rate_to_value_state_t *state, int ds_type, cdtime_t t);
+
 /* Converts a service name (a string) to a port number
  * (in the range [1-65535]). Returns less than zero on error. */
 int service_name_to_port_number (const char *service_name);
-- 
2.30.2