format time header 5% faster than before

logs/logger.go

@@ -36,43 +36,44 @@ func (lg *logWriter) println(when time.Time, msg string) {
 	lg.Unlock()
 }
 
+const y1 = `0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999`
+const y2 = `0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789`
+const mo1 = `000000000111`
+const mo2 = `123456789012`
+const d1 = `0000000001111111111222222222233`
+const d2 = `1234567890123456789012345678901`
+const h1 = `000000000011111111112222`
+const h2 = `012345678901234567890123`
+const mi1 = `000000000011111111112222222222333333333344444444445555555555`
+const mi2 = `012345678901234567890123456789012345678901234567890123456789`
+const s1 = `000000000011111111112222222222333333333344444444445555555555`
+const s2 = `012345678901234567890123456789012345678901234567890123456789`
+
 func formatTimeHeader(when time.Time) ([]byte, int) {
 	y, mo, d := when.Date()
 	h, mi, s := when.Clock()
-	//len(2006/01/02 15:03:04)==19
+	//len("2006/01/02 15:03:04 ")==20
 	var buf [20]byte
-	t := 3
-	for y >= 10 {
-		p := y / 10
-		buf[t] = byte('0' + y - p*10)
-		y = p
-		t--
-	}
-	buf[0] = byte('0' + y)
+
+	buf[0] = '2'
+	buf[1] = '0'
+	buf[2] = y1[y-2000]
+	buf[3] = y2[y-2000]
 	buf[4] = '/'
-	if mo > 9 {
-		buf[5] = '1'
-		buf[6] = byte('0' + mo - 9)
-	} else {
-		buf[5] = '0'
-		buf[6] = byte('0' + mo)
-	}
+	buf[5] = mo1[mo]
+	buf[6] = mo2[mo]
 	buf[7] = '/'
-	t = d / 10
-	buf[8] = byte('0' + t)
-	buf[9] = byte('0' + d - t*10)
+	buf[8] = d1[d]
+	buf[9] = d2[d]
 	buf[10] = ' '
-	t = h / 10
-	buf[11] = byte('0' + t)
-	buf[12] = byte('0' + h - t*10)
+	buf[11] = h1[h]
+	buf[12] = h2[h]
 	buf[13] = ':'
-	t = mi / 10
-	buf[14] = byte('0' + t)
-	buf[15] = byte('0' + mi - t*10)
+	buf[14] = mi1[mi]
+	buf[15] = mi2[mi]
 	buf[16] = ':'
-	t = s / 10
-	buf[17] = byte('0' + t)
-	buf[18] = byte('0' + s - t*10)
+	buf[17] = s1[s]
+	buf[18] = s2[s]
 	buf[19] = ' '
 
 	return buf[0:], d