Add error calculation to morris

morris/error/error.go

@@ -0,0 +1,38 @@
+// Prints error rates of Morris counter using different m's.
+package main
+
+import (
+	"fmt"
+
+	"github.com/fluhus/gostuff/gnum"
+	"github.com/fluhus/gostuff/morris"
+	"github.com/fluhus/gostuff/ptimer"
+)
+
+const (
+	upto = 10000000
+	reps = 100
+)
+
+func main() {
+	ms := []uint{1, 3, 10, 30, 100, 300, 1000, 3000, 10000}
+	var errs []float64
+	for _, m := range ms {
+		pt := ptimer.NewMessage(fmt.Sprint("{} (", m, ")"))
+		err := 0.0
+		for rep := 1; rep <= reps; rep++ {
+			c := uint(0)
+			for i := 1; i <= upto; i++ {
+				c = morris.Raise(c, m)
+				r := morris.Restore(c, m)
+				err += float64(gnum.Abs(int(i)-int(r))) / float64(i)
+				pt.Inc()
+			}
+		}
+		pt.Done()
+		errs = append(errs, err/upto/reps)
+	}
+	for i := range ms {
+		fmt.Printf("// % 10d: %.1f%%\n", ms[i], errs[i]*100)
+	}
+}

morris/morris.go

@@ -11,6 +11,20 @@
 // A single counter should use the same m for all calls to Raise and Restore.
 //
 // This package is experimental.
+//
+// # Error rates
+//
+// Average error rates for different values of m:
+//
+//	    1: 54.2%
+//	    3: 31.1%
+//	   10: 15.5%
+//	   30: 8.8%
+//	  100: 4.6%
+//	  300: 2.5%
+//	 1000: 1.6%
+//	 3000: 0.9%
+//	10000: 0.5%
 package morris
 
 import (