add time tracker

profiling/timing.md

@@ -5,20 +5,62 @@ as opposed to utilizing profiler tools/frameworks to validate assumptions.
 
 Time measurements can be performed by utilizing `time` package and `defer` statements.
 
+Also, you can use `TimeTracker` to track each step cost for a function.
+
 ## Implementation
 
 ```go
 package profile
 
 import (
-    "time"
+	"fmt"
-    "log"
+	"log"
+	"time"
 )
 
 func Duration(invocation time.Time, name string) {
-    elapsed := time.Since(invocation)
+	elapsed := time.Since(invocation)
+	log.Printf("%s lasted %s", name, elapsed)
+}
 
-    log.Printf("%s lasted %s", name, elapsed)
+type timeEvent struct {
+	event string
+	cost  time.Duration
+}
+
+type TimeTracker struct {
+	action string
+	start  time.Time
+	events []timeEvent
+}
+
+func NewTrack(action string) *TimeTracker {
+	now := time.Now()
+	return &TimeTracker{
+		action: action,
+		start:  now,
+		events: make([]timeEvent, 0, 5),
+	}
+}
+
+func (tk *TimeTracker) Track(name string) {
+	curEvent := timeEvent{
+		event: name,
+		cost:  time.Since(tk.start),
+	}
+	tk.events = append(tk.events, curEvent)
+	tk.start = time.Now()
+}
+
+func (tk *TimeTracker) Print() {
+	total := time.Now().Sub(tk.start)
+	var pairs string
+	for _, ev := range tk.events {
+		pairs += fmt.Sprintf("%s:%s ", ev.event, ev.cost)
+	}
+	if pairs != "" {
+		log.Printf("timeTrack:%s total lasted:%s %s\n", tk.action, total, pairs)
+	}
 }
 ```
 
@@ -35,4 +77,23 @@ func IntFactorial(x big.Int) *big.Int {
 
     return x.Set(y)
 }
+
+func IntFactorialTrack(x big.Int) *big.Int {
+	tk := profile.NewTrack("IntFactorialTrack")
+	defer tk.Print()
+
+	y := big.NewInt(1)
+	for one := big.NewInt(1); x.Sign() > 0; x.Sub(x, one) {
+		y.Mul(y, x)
+	}
+	tk.Track("step_one")
+	
+	z := big.NewInt(1)
+	for one := big.NewInt(1); x.Sign() > 0; x.Sub(x, one) {
+		z.Mul(z, x)
+	}
+	tk.Track("step_two")
+	
+	return x.Set(y.Mul(y,z))
+}
 ```