reduce heap allocations in protocol (#361)

Summary:
Pull Request resolved: #361

Optimize few conversions using bit shifts.

Reviewed By: leoleovich

Differential Revision: D58408274

fbshipit-source-id: 34af37f0f8d1a25bb22f93cd184f0511bee5f843

ptp/protocol/types.go

@@ -199,15 +199,13 @@ func (c ClockIdentity) String() string {
 
 // MAC turns ClockIdentity into the MAC address it was based upon. EUI-48 is assumed.
 func (c ClockIdentity) MAC() net.HardwareAddr {
-	asBytes := [8]byte{}
-	binary.BigEndian.PutUint64(asBytes[:], uint64(c))
 	mac := make(net.HardwareAddr, 6)
-	mac[0] = asBytes[0]
-	mac[1] = asBytes[1]
-	mac[2] = asBytes[2]
-	mac[3] = asBytes[5]
-	mac[4] = asBytes[6]
-	mac[5] = asBytes[7]
+	mac[0] = byte(c >> 56)
+	mac[1] = byte(c >> 48)
+	mac[2] = byte(c >> 40)
+	mac[3] = byte(c >> 16)
+	mac[4] = byte(c >> 8)
+	mac[5] = byte(c)
 	return mac
 }
 
@@ -279,8 +277,8 @@ func (s PTPSeconds) Empty() bool {
 
 // Seconds returns number of seconds as uint64
 func (s PTPSeconds) Seconds() uint64 {
-	b := append([]byte{0x0, 0x0}, s[:]...)
-	return binary.BigEndian.Uint64(b)
+	return uint64(s[5]) | uint64(s[4])<<8 | uint64(s[3])<<16 | uint64(s[2])<<24 |
+		uint64(s[1])<<32 | uint64(s[0])<<40
 }
 
 // Time returns number of seconds in as Time
@@ -304,11 +302,14 @@ func NewPTPSeconds(t time.Time) PTPSeconds {
 	if t.IsZero() {
 		return PTPSeconds{}
 	}
-	b := [8]byte{}
+	v := uint64(t.Unix())
 	s := PTPSeconds{}
-	binary.BigEndian.PutUint64(b[:], uint64(t.Unix()))
-	// take last 6 bytes from 8 bytes of int64
-	copy(s[:], b[2:])
+	s[0] = byte(v >> 40)
+	s[1] = byte(v >> 32)
+	s[2] = byte(v >> 24)
+	s[3] = byte(v >> 16)
+	s[4] = byte(v >> 8)
+	s[5] = byte(v)
 	return s
 }
 
@@ -354,10 +355,13 @@ func NewTimestamp(t time.Time) Timestamp {
 	ts := Timestamp{
 		Nanoseconds: uint32(t.Nanosecond()),
 	}
-	b := [8]byte{}
-	binary.BigEndian.PutUint64(b[:], uint64(t.Unix()))
-	// take last 6 bytes from 8 bytes of int64
-	copy(ts.Seconds[:], b[2:])
+	v := uint64(t.Unix())
+	ts.Seconds[0] = byte(v >> 40)
+	ts.Seconds[1] = byte(v >> 32)
+	ts.Seconds[2] = byte(v >> 24)
+	ts.Seconds[3] = byte(v >> 16)
+	ts.Seconds[4] = byte(v >> 8)
+	ts.Seconds[5] = byte(v)
 	return ts
 }