time: optimize the performance of the function appendFormatRFC3339

src/time/export_test.go

@@ -134,6 +134,8 @@ var StdChunkNames = map[int]string{
 var Quote = quote
 
 var AppendInt = appendInt
+var AppendIntWidth2 = appendIntWidth2
+var AppendIntWidth4 = appendIntWidth4
 var AppendFormatAny = Time.appendFormat
 var AppendFormatRFC3339 = Time.appendFormatRFC3339
 var ParseAny = parse

src/time/format.go

@@ -464,6 +464,36 @@ func appendInt(b []byte, x int, width int) []byte {
 	return b
 }
 
+const unitsDigit = "01234567890123456789012345678901234567890123456789" +
+	"01234567890123456789012345678901234567890123456789"
+const tensDigit = "00000000001111111111222222222233333333334444444444" +
+	"55555555556666666666777777777788888888889999999999"
+
+// appendIntWidth2 special scenario for appendInt, with parameter width=2
+// Only applicable to integers with absolute value less than 100
+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 {
+		return appendInt(b, x, 4)
+	}
+	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
 }
 

src/time/format_test.go

@@ -1091,3 +1091,70 @@ func FuzzParseRFC3339(f *testing.F) {
 		}
 	})
 }
+
+func TestAppendIntWidth(t *testing.T) {
+	values := []int{0, -1, 1, 10, -10, 99, -99}
+	for _, v := range values {
+		exp := AppendInt(nil, v, 2)
+		got := AppendIntWidth2(nil, v)
+		if !bytes.Equal(got, exp) {
+			t.Errorf("AppendIntWidth2(%d) = %s, want %s", v, got, exp)
+		}
+	}
+
+	got := AppendIntWidth2(nil, 199)
+	if !bytes.Equal(got, []byte("99")) {
+		t.Errorf("AppendIntWidth2(199) = %s, want %s", got, []byte("99"))
+	}
+
+	values = append(values, 9999, -9999, 10001)
+	for _, v := range values {
+		exp := AppendInt(nil, v, 4)
+		got := AppendIntWidth4(nil, v)
+		if !bytes.Equal(got, exp) {
+			t.Errorf("AppendIntWidth4(%d) = %s, want %s", v, got, exp)
+		}
+	}
+}
+
+func BenchmarkAppendIntWidth2(b *testing.B) {
+	b.Run("name=AppendInt", func(b *testing.B) {
+		var buf = make([]byte, 0, 8)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			buf = AppendInt(buf[:0], 36, 2)
+		}
+	})
+	b.Run("name=AppendIntWidth2", func(b *testing.B) {
+		var buf = make([]byte, 0, 8)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			buf = AppendIntWidth2(buf[:0], 36)
+		}
+	})
+}
+
+func BenchmarkAppendIntWidth4(b *testing.B) {
+	b.Run("name=AppendInt", func(b *testing.B) {
+		var buf = make([]byte, 0, 8)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			buf = AppendInt(buf[:0], 360, 4)
+		}
+	})
+	b.Run("name=AppendIntWidth4", func(b *testing.B) {
+		var buf = make([]byte, 0, 8)
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			buf = AppendIntWidth4(buf[:0], 360)
+		}
+	})
+}
+
+func BenchmarkTimeFormatRFC3339(b *testing.B) {
+	tm := Now()
+	buf := make([]byte, 0, 64)
+	for i := 0; i < b.N; i++ {
+		buf = tm.AppendFormat(buf[:0], RFC3339)
+	}
+}