math/big: implement GobDecode/Encode for big.Float

Added GobEncode/Decode and a test for them.

Fixes #14593

Change-Id: Ic8d3efd24d0313a1a66f01da293c4c1fd39764a8
Reviewed-on: https://go-review.googlesource.com/21755
Reviewed-by: Robert Griesemer <gri@golang.org>

diff --git a/src/math/big/floatmarsh.go b/src/math/big/floatmarsh.go
index 44987ee03a61367c3a1ab38a0db3c07c2700da7e..6127aa2e83d0042fe093c32a8d2611739d8a8465 100644 (file)
--- a/src/math/big/floatmarsh.go
+++ b/src/math/big/floatmarsh.go
@@ -6,7 +6,70 @@
 
 package big
 
-import "fmt"
+import (
+       "encoding/binary"
+       "fmt"
+)
+
+// Gob codec version. Permits backward-compatible changes to the encoding.
+const floatGobVersion byte = 1
+
+// GobEncode implements the gob.GobEncoder interface.
+func (x *Float) GobEncode() ([]byte, error) {
+       if x == nil {
+               return nil, nil
+       }
+       sz := 1 + 1 + 4 // version + mode|acc|form|neg (3+2+2+1bit) + prec
+       if x.form == finite {
+               sz += 4 + int((x.prec+(_W-1))/_W)*_S // exp + mant
+       }
+       buf := make([]byte, sz)
+
+       buf[0] = floatGobVersion
+       b := byte(x.mode&7)<<5 | byte((x.acc+1)&3)<<3 | byte(x.form&3)<<1
+       if x.neg {
+               b |= 1
+       }
+       buf[1] = b
+       binary.BigEndian.PutUint32(buf[2:], x.prec)
+       if x.form == finite {
+               binary.BigEndian.PutUint32(buf[6:], uint32(x.exp))
+               x.mant.bytes(buf[10:])
+       }
+       return buf, nil
+}
+
+// GobDecode implements the gob.GobDecoder interface.
+func (z *Float) GobDecode(buf []byte) error {
+       if len(buf) == 0 {
+               // Other side sent a nil or default value.
+               *z = Float{}
+               return nil
+       }
+
+       if buf[0] != floatGobVersion {
+               return fmt.Errorf("Float.GobDecode: encoding version %d not supported", buf[0])
+       }
+
+       b := buf[1]
+       z.mode = RoundingMode((b >> 5) & 7)
+       z.acc = Accuracy((b>>3)&3) - 1
+       z.form = form((b >> 1) & 3)
+       z.neg = b&1 != 0
+
+       oldPrec := uint(z.prec)
+       z.prec = binary.BigEndian.Uint32(buf[2:])
+
+       if z.form == finite {
+               z.exp = int32(binary.BigEndian.Uint32(buf[6:]))
+               z.mant = z.mant.setBytes(buf[10:])
+       }
+
+       if oldPrec != 0 {
+               z.SetPrec(oldPrec)
+       }
+       return nil
+}
 
 // MarshalText implements the encoding.TextMarshaler interface.
 // Only the Float value is marshaled (in full precision), other

diff --git a/src/math/big/floatmarsh_test.go b/src/math/big/floatmarsh_test.go
index d7ef2fca68fcc744213e014cc17225deee6e4cd7..f726c35e99ff9cff10f6674afbd3e88e763d707c 100644 (file)
--- a/src/math/big/floatmarsh_test.go
+++ b/src/math/big/floatmarsh_test.go
@@ -5,7 +5,10 @@
 package big
 
 import (
+       "bytes"
+       "encoding/gob"
        "encoding/json"
+       "io"
        "testing"
 )
 
@@ -23,6 +26,66 @@ var floatVals = []string{
        "Inf",
 }
 
+func TestFloatGobEncoding(t *testing.T) {
+       var medium bytes.Buffer
+       for _, test := range floatVals {
+               for _, sign := range []string{"", "+", "-"} {
+                       for _, prec := range []uint{0, 1, 2, 10, 53, 64, 100, 1000} {
+                               medium.Reset() // empty buffer for each test case (in case of failures)
+                               enc := gob.NewEncoder(&medium)
+                               dec := gob.NewDecoder(&medium)
+                               x := sign + test
+                               var tx Float
+                               _, _, err := tx.SetPrec(prec).Parse(x, 0)
+                               if err != nil {
+                                       t.Errorf("parsing of %s (prec = %d) failed (invalid test case): %v", x, prec, err)
+                                       continue
+                               }
+                               tx.SetMode(ToPositiveInf)
+                               if err := enc.Encode(&tx); err != nil {
+                                       t.Errorf("encoding of %v (prec = %d) failed: %v", &tx, prec, err)
+                                       continue
+                               }
+
+                               var rx Float
+                               if err := dec.Decode(&rx); err != nil {
+                                       t.Errorf("decoding of %v (prec = %d) failed: %v", &tx, prec, err)
+                                       continue
+                               }
+
+                               if rx.Cmp(&tx) != 0 {
+                                       t.Errorf("transmission of %s failed: got %s want %s", x, rx.String(), tx.String())
+                                       continue
+                               }
+
+                               if rx.Mode() != ToPositiveInf {
+                                       t.Errorf("transmission of %s's mode failed: got %s want %s", x, rx.Mode(), ToPositiveInf)
+                               }
+                       }
+               }
+       }
+}
+func TestFloatCorruptGob(t *testing.T) {
+       var buf bytes.Buffer
+       tx := NewFloat(4 / 3).SetPrec(1000).SetMode(ToPositiveInf)
+       if err := gob.NewEncoder(&buf).Encode(tx); err != nil {
+               t.Fatal(err)
+       }
+       b := buf.Bytes()
+       var rx Float
+       if err := gob.NewDecoder(bytes.NewReader(b)).Decode(&rx); err != nil {
+               t.Fatal(err)
+       }
+       var rx2 Float
+       if err := gob.NewDecoder(bytes.NewReader(b[:10])).Decode(&rx2); err != io.ErrUnexpectedEOF {
+               t.Errorf("expected io.ErrUnexpectedEOF, got %v", err)
+       }
+       b[1] = 0
+       if err := gob.NewDecoder(bytes.NewReader(b)).Decode(&rx); err == nil {
+               t.Fatal("expected a version error, got nil")
+       }
+
+}
 func TestFloatJSONEncoding(t *testing.T) {
        for _, test := range floatVals {
                for _, sign := range []string{"", "+", "-"} {