Add ratio calculation to take the ratio of two calculations.

perf/go/parser/funcs.go

 package parser
 
 import (
         "fmt"
         "net/url"
         "strconv"
 
         "skia.googlesource.com/buildbot.git/perf/go/config"
         "skia.googlesource.com/buildbot.git/perf/go/types"
         "skia.googlesource.com/buildbot.git/perf/go/vec"
@@ skipping 157 matching lines @@
                 }
         }
         return []*types.PerfTrace{ret}, nil
 }
 
 func (AveFunc) Describe() string {
         return `ave() averages the values of all argument traces into a single trace.`
 }
 
 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.")
+        }
+
+        traces, err := node.Args[0].Eval(ctx)

[jcgregorio, 2014/09/29 15:09:22]

Yes, you'll need to call Eval on both Args[0] and Args[1].

[tfarina, 2014/10/01 02:30:16]

Done.

+        if err != nil {
+                return nil, fmt.Errorf("ratio() argument failed to evaluate: %s", err)
+        }
+
+        if len(traces) == 0 {
+                return traces, nil
+        }
+
+        ret := types.NewPerfTraceN(len(traces[0].Values))

[tfarina, 2014/09/30 13:35:14]

Where the calc will go here?

You said in the e-mail the calculation could be:
a.Values[i] / b.Values[i]

Does that translates to the following?

traces[0].Values[i] / traces[1].Values[i]

This 'i' will come from a for loop?

[jcgregorio, 2014/09/30 14:59:03]

Yes, look at

  for i, _ := range ret.Values

in AveFunc.Eval.

[tfarina, 2014/10/01 02:30:16]

I'm not sure yet how to proceed. Now I have tracesA and tracesB.

Will they have the same length?

[jcgregorio, 2014/10/01 03:48:58]

Yes, they will always have the same length.

On 2014/10/01 02:30:16, tfarina wrote:

+        return []*types.PerfTrace{ret}, nil
+}
+
+func (RatioFunc) Describe() string {
+        return `ratio() .`

[tfarina, 2014/09/30 13:35:14]

could the description be something like:

"ratio() returns the ratio of two calculations."

Suggest something better?

[jcgregorio, 2014/09/30 14:59:03]

`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.`

[tfarina, 2014/10/01 02:30:16]

Done.

+}
+
+var ratioFunc = RatioFunc{}