Make a public function for computing total CPU time

This function used to be a private part of process.go.

Since I needed that functionality however I think it's better to make it public
than for me to copy it into my own code.

As a side effect of this change, I also fixed a bug in the function where Stolen
was not part of the sum. Having the function close to the CPUTimesStat
declaration will make problems like this less likely to re-occur in the future.

cpu/cpu.go

@@ -63,6 +63,13 @@ func (c CPUTimesStat) String() string {
 	return `{` + strings.Join(v, ",") + `}`
 }
 
+// Total returns the total number of seconds in a CPUTimesStat
+func (c CPUTimesStat) Total() float64 {
+	total := c.User + c.System + c.Nice + c.Iowait + c.Irq + c.Softirq + c.Steal +
+		c.Guest + c.GuestNice + c.Idle + c.Stolen
+	return total
+}
+
 func (c CPUInfoStat) String() string {
 	s, _ := json.Marshal(c)
 	return string(s)

process/process.go

@@ -141,13 +141,7 @@ func calculatePercent(t1, t2 *cpu.CPUTimesStat, delta float64, numcpu int) float
 	if delta == 0 {
 		return 0
 	}
-	delta_proc := totalCpuTime(t2) - totalCpuTime(t1)
+	delta_proc := t2.Total() - t1.Total()
 	overall_percent := ((delta_proc / delta) * 100) * float64(numcpu)
 	return overall_percent
 }
-
-func totalCpuTime(t *cpu.CPUTimesStat) float64 {
-	total := t.User + t.System + t.Nice + t.Iowait + t.Irq + t.Softirq + t.Steal +
-		t.Guest + t.GuestNice + t.Idle
-	return total
-}