1// Copyright 2015 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// This file implements encoding/decoding of Rats.
6
7package big
8
9import (
10	"encoding/binary"
11	"errors"
12	"fmt"
13)
14
15// Gob codec version. Permits backward-compatible changes to the encoding.
16const ratGobVersion byte = 1
17
18// GobEncode implements the gob.GobEncoder interface.
19func (x *Rat) GobEncode() ([]byte, error) {
20	if x == nil {
21		return nil, nil
22	}
23	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)
24	i := x.b.abs.bytes(buf)
25	j := x.a.abs.bytes(buf[:i])
26	n := i - j
27	if int(uint32(n)) != n {
28		// this should never happen
29		return nil, errors.New("Rat.GobEncode: numerator too large")
30	}
31	binary.BigEndian.PutUint32(buf[j-4:j], uint32(n))
32	j -= 1 + 4
33	b := ratGobVersion << 1 // make space for sign bit
34	if x.a.neg {
35		b |= 1
36	}
37	buf[j] = b
38	return buf[j:], nil
39}
40
41// GobDecode implements the gob.GobDecoder interface.
42func (z *Rat) GobDecode(buf []byte) error {
43	if len(buf) == 0 {
44		// Other side sent a nil or default value.
45		*z = Rat{}
46		return nil
47	}
48	b := buf[0]
49	if b>>1 != ratGobVersion {
50		return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
51	}
52	const j = 1 + 4
53	i := j + binary.BigEndian.Uint32(buf[j-4:j])
54	z.a.neg = b&1 != 0
55	z.a.abs = z.a.abs.setBytes(buf[j:i])
56	z.b.abs = z.b.abs.setBytes(buf[i:])
57	return nil
58}
59
60// MarshalText implements the encoding.TextMarshaler interface.
61func (x *Rat) MarshalText() (text []byte, err error) {
62	if x.IsInt() {
63		return x.a.MarshalText()
64	}
65	return x.marshal(), nil
66}
67
68// UnmarshalText implements the encoding.TextUnmarshaler interface.
69func (z *Rat) UnmarshalText(text []byte) error {
70	// TODO(gri): get rid of the []byte/string conversion
71	if _, ok := z.SetString(string(text)); !ok {
72		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
73	}
74	return nil
75}
76