math/big: move Int/Rat gob/json/xml functionality in separate files

Like int/rat/float conversions, move this functionality into separate
implementation and test files.

No implementation changes besides the move.

Change-Id: If19c45f5a72a57b95cbce2329724693ae5a4807d
Reviewed-on: https://go-review.googlesource.com/14997
Reviewed-by: Alan Donovan <adonovan@google.com>

1 files changed, 71 insertions, 0 deletions

diff --git a/src/math/big/ratmarsh.go b/src/math/big/ratmarsh.go
new file mode 100644
index 0000000000..b79cbe6652
--- /dev/null
+++ b/src/math/big/ratmarsh.go
@@ -0,0 +1,71 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements encoding/decoding of Rats.
+
+package big
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+// Gob codec version. Permits backward-compatible changes to the encoding.
+const ratGobVersion byte = 1
+
+// GobEncode implements the gob.GobEncoder interface.
+func (x *Rat) GobEncode() ([]byte, error) {
+	if x == nil {
+		return nil, nil
+	}
+	buf := make([]byte, 1+4+(len(x.a.abs)+len(x.b.abs))*_S) // extra bytes for version and sign bit (1), and numerator length (4)
+	i := x.b.abs.bytes(buf)
+	j := x.a.abs.bytes(buf[:i])
+	n := i - j
+	if int(uint32(n)) != n {
+		// this should never happen
+		return nil, errors.New("Rat.GobEncode: numerator too large")
+	}
+	binary.BigEndian.PutUint32(buf[j-4:j], uint32(n))
+	j -= 1 + 4
+	b := ratGobVersion << 1 // make space for sign bit
+	if x.a.neg {
+		b |= 1
+	}
+	buf[j] = b
+	return buf[j:], nil
+}
+
+// GobDecode implements the gob.GobDecoder interface.
+func (z *Rat) GobDecode(buf []byte) error {
+	if len(buf) == 0 {
+		// Other side sent a nil or default value.
+		*z = Rat{}
+		return nil
+	}
+	b := buf[0]
+	if b>>1 != ratGobVersion {
+		return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
+	}
+	const j = 1 + 4
+	i := j + binary.BigEndian.Uint32(buf[j-4:j])
+	z.a.neg = b&1 != 0
+	z.a.abs = z.a.abs.setBytes(buf[j:i])
+	z.b.abs = z.b.abs.setBytes(buf[i:])
+	return nil
+}
+
+// MarshalText implements the encoding.TextMarshaler interface.
+func (r *Rat) MarshalText() (text []byte, err error) {
+	return []byte(r.RatString()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface.
+func (r *Rat) UnmarshalText(text []byte) error {
+	if _, ok := r.SetString(string(text)); !ok {
+		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
+	}
+	return nil
+}