Add MessagePack Marshal and Unmarshal

.gitignore

@@ -4,6 +4,7 @@
 # IntelliJ
 .idea/
 *.iml
+*.sum
 
 # VS code
 *.code-workspace

decimal_gen.go

@@ -0,0 +1,90 @@
+package decimal
+
+import (
+	"errors"
+)
+
+var (
+	errShortBytes = errors.New("msgp: too few bytes left to read object")
+)
+
+
+// MarshalMsg implements msgp.Marshaler
+func (d Decimal) MarshalMsg(b []byte) (o []byte, err error) {
+	o = require(b, d.Msgsize())
+	str := d.String()
+	sz := len(str)
+	if sz > 30 {
+		sz = 30
+		if str[29] == '.' {
+			sz = 29
+		}
+
+		str = str[:sz]
+	}
+
+	o, n := ensure(b, 1+sz)
+	o[n] = byte(0xa0 | sz)
+	n++
+
+	return o[:n+copy(o[n:], str)], nil
+}
+
+// UnmarshalMsg implements msgp.Unmarshaler
+func (d *Decimal) UnmarshalMsg(b []byte) (o []byte, err error) {
+	l := len(b)
+	if l < 1 {
+		return nil, errShortBytes
+	}
+
+	sz := int(b[0] & 0x1f)
+	if len(b[1:]) < sz {
+		err = errShortBytes
+		return
+	}
+	if *d, err = NewFromString(string(b[1 : sz+1])); err == nil {
+		o = b[sz:]
+	}
+	return
+}
+
+// Msgsize returns an upper bound estimate of the number of bytes occupied by the serialized message
+func (d Decimal) Msgsize() int {
+	return 31
+}
+
+// Require ensures that cap(old)-len(old) >= extra.
+func require(old []byte, extra int) []byte {
+	l := len(old)
+	c := cap(old)
+	r := l + extra
+	if c >= r {
+		return old
+	} else if l == 0 {
+		return make([]byte, 0, extra)
+	}
+	// the new size is the greater
+	// of double the old capacity
+	// and the sum of the old length
+	// and the number of new bytes
+	// necessary.
+	c <<= 1
+	if c < r {
+		c = r
+	}
+	n := make([]byte, l, c)
+	copy(n, old)
+	return n
+}
+
+// ensure 'sz' extra bytes in 'b' btw len(b) and cap(b)
+func ensure(b []byte, sz int) ([]byte, int) {
+	l := len(b)
+	c := cap(b)
+	if c-l < sz {
+		o := make([]byte, (2*c)+sz) // exponential growth
+		n := copy(o, b)
+		return o[:n+sz], n
+	}
+	return b[:l+sz], l
+}

decimal_test.go

@@ -2,6 +2,7 @@ package decimal
 
 import (
 	"database/sql/driver"
+	"encoding/base64"
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
@@ -3339,3 +3340,18 @@ func ExampleNewFromFloat() {
 	//0.123123123123123
 	//-10000000000000
 }
+
+func TestMsgPack(t *testing.T) {
+	d, _ := NewFromString("79228162514264337593543950334.123222")
+	out, err := d.MarshalMsg(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Log(base64.StdEncoding.EncodeToString(out))
+
+	var d2 = Decimal{}
+	if _, err = d2.UnmarshalMsg(out); err != nil {
+		t.Fatal(err)
+	}
+	t.Log(d2.String())
+}

go.mod

@@ -1,3 +1,3 @@
-module github.com/shopspring/decimal
+module github.com/piyongcai/decimal
 
 go 1.13