optimize the performance of the function appendFormatRFC3339

Author: fx408

src/time/format.go

@@ -464,6 +464,33 @@ func appendInt(b []byte, x int, width int) []byte {
 	return b
 }
 
+const unitsDigit = "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
+const tensDigit = "0000000000111111111122222222223333333333444444444455555555556666666666777777777788888888889999999999"
+
+// appendIntWidth2 special scenario for appendInt, with parameter width=2
+func appendIntWidth2(b []byte, x int) []byte {
+	if x < 0 {
+		b = append(b, '-')
+		x = -x
+	}
+	if x >= 1e2 {
+		x %= 1e2
+	}
+	return append(b, tensDigit[x], unitsDigit[x])
+}
+
+// appendIntWidth4 special scenario for appendInt, with parameter width=4
+func appendIntWidth4(b []byte, x int) []byte {
+	if x < 0 {
+		b = append(b, '-')
+		x = -x
+	}
+	if x >= 1e4 {
+		x %= 1e4
+	}
+	return append(b, tensDigit[x/1e2], unitsDigit[x/1e2], tensDigit[x%1e2], unitsDigit[x%1e2])
+}
+
 // Never printed, just needs to be non-nil for return by atoi.
 var errAtoi = errors.New("time: invalid number")
 

src/time/format_rfc3339.go

@@ -20,21 +20,21 @@ func (t Time) appendFormatRFC3339(b []byte, nanos bool) []byte {
 
 	// Format date.
 	year, month, day := abs.days().date()
-	b = appendInt(b, year, 4)
+	b = appendIntWidth4(b, year)
 	b = append(b, '-')
-	b = appendInt(b, int(month), 2)
+	b = appendIntWidth2(b, int(month))
 	b = append(b, '-')
-	b = appendInt(b, day, 2)
+	b = appendIntWidth2(b, day)
 
 	b = append(b, 'T')
 
 	// Format time.
 	hour, min, sec := abs.clock()
-	b = appendInt(b, hour, 2)
+	b = appendIntWidth2(b, hour)
 	b = append(b, ':')
-	b = appendInt(b, min, 2)
+	b = appendIntWidth2(b, min)
 	b = append(b, ':')
-	b = appendInt(b, sec, 2)
+	b = appendIntWidth2(b, sec)
 
 	if nanos {
 		std := stdFracSecond(stdFracSecond9, 9, '.')
@@ -53,9 +53,9 @@ func (t Time) appendFormatRFC3339(b []byte, nanos bool) []byte {
 	} else {
 		b = append(b, '+')
 	}
-	b = appendInt(b, zone/60, 2)
+	b = appendIntWidth2(b, zone/60)
 	b = append(b, ':')
-	b = appendInt(b, zone%60, 2)
+	b = appendIntWidth2(b, zone%60)
 	return b
 }