Merge pull request #971 from wladh/crc32castagnoli

Add support for Castagnoli polynomial for CRC32 computation

crc32_field.go

@@ -6,9 +6,19 @@ import (
 	"hash/crc32"
 )
 
+type crcPolynomial int8
+
+const (
+	crcIEEE crcPolynomial = iota
+	crcCastagnoli
+)
+
+var castagnoliTable = crc32.MakeTable(crc32.Castagnoli)
+
 // crc32Field implements the pushEncoder and pushDecoder interfaces for calculating CRC32s.
 type crc32Field struct {
 	startOffset int
+	polynomial  crcPolynomial
 }
 
 func (c *crc32Field) saveOffset(in int) {
@@ -19,14 +29,24 @@ func (c *crc32Field) reserveLength() int {
 	return 4
 }
 
+func newCRC32Field(polynomial crcPolynomial) *crc32Field {
+	return &crc32Field{polynomial: polynomial}
+}
+
 func (c *crc32Field) run(curOffset int, buf []byte) error {
-	crc := crc32.ChecksumIEEE(buf[c.startOffset+4 : curOffset])
+	crc, err := c.crc(curOffset, buf)
+	if err != nil {
+		return err
+	}
 	binary.BigEndian.PutUint32(buf[c.startOffset:], crc)
 	return nil
 }
 
 func (c *crc32Field) check(curOffset int, buf []byte) error {
-	crc := crc32.ChecksumIEEE(buf[c.startOffset+4 : curOffset])
+	crc, err := c.crc(curOffset, buf)
+	if err != nil {
+		return err
+	}
 
 	expected := binary.BigEndian.Uint32(buf[c.startOffset:])
 	if crc != expected {
@@ -35,3 +55,15 @@ func (c *crc32Field) check(curOffset int, buf []byte) error {
 
 	return nil
 }
+func (c *crc32Field) crc(curOffset int, buf []byte) (uint32, error) {
+	var tab *crc32.Table
+	switch c.polynomial {
+	case crcIEEE:
+		tab = crc32.IEEETable
+	case crcCastagnoli:
+		tab = castagnoliTable
+	default:
+		return 0, PacketDecodingError{"invalid CRC type"}
+	}
+	return crc32.Checksum(buf[c.startOffset+4:curOffset], tab), nil
+}

message.go

@@ -37,7 +37,7 @@ type Message struct {
 }
 
 func (m *Message) encode(pe packetEncoder) error {
-	pe.push(&crc32Field{})
+	pe.push(newCRC32Field(crcIEEE))
 
 	pe.putInt8(m.Version)
 
@@ -112,7 +112,7 @@ func (m *Message) encode(pe packetEncoder) error {
 }
 
 func (m *Message) decode(pd packetDecoder) (err error) {
-	err = pd.push(&crc32Field{})
+	err = pd.push(newCRC32Field(crcIEEE))
 	if err != nil {
 		return err
 	}