Add ratio calculation to take the ratio of two calculations.

perf/go/parser/funcs.go

Index: perf/go/parser/funcs.go
diff --git a/perf/go/parser/funcs.go b/perf/go/parser/funcs.go
index bca448e00a1770f894ff72a174e725aca02fff43..b5a7cbc9784a4b648ff91482bc7caf200b079ad2 100644
--- a/perf/go/parser/funcs.go
+++ b/perf/go/parser/funcs.go
@@ -175,3 +175,34 @@ func (AveFunc) Describe() string {
 }
 
 var aveFunc = AveFunc{}
+
+type RatioFunc struct{}
+
+func (RatioFunc) Eval(ctx *Context, node *Node) ([]*types.PerfTrace, error) {
+	if len(node.Args) != 2 {
+		return nil, fmt.Errorf("ratio() takes two arguments")
+	}
+
+	tracesA, err := node.Args[0].Eval(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("ratio() argument failed to evaluate: %s", err)
+	}
+
+	tracesB, err := node.Args[1].Eval(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("ratio() argument failed to evaluate: %s", err)
+	}
+
+	ret := types.NewPerfTraceN(len(tracesA[0].Values))
+	for i, _ := range ret.Values {
+		ret.Values[i] = tracesA[0].Values[i] / tracesB[1].Values[i]

[jcgregorio, 2014/10/18 00:19:13]

Either check for division by 0 before hand, or check the result of the division
for +-Inf after the fact and replace them with MISSING_DATA_SENTINEL if found.

[tfarina, 2014/10/18 03:15:46]

Done.

+	}
+	return []*types.PerfTrace{ret}, nil
+}
+
+func (RatioFunc) Describe() string {
+	return `ratio(a, b) returns the point by point ratio of two traces.
+                That is, it returns a trace with a[i]/b[i] for every point in a and b.`
+}
+
+var ratioFunc = RatioFunc{}