// 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" "math" ) // Gob codec version. Permits backward-compatible changes to the encoding. const ratGobVersion byte = 1 // GobEncode implements the [encoding/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 [encoding/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 } if len(buf) < 5 { return errors.New("Rat.GobDecode: buffer too small") } b := buf[0] if b>>1 != ratGobVersion { return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1) } const j = 1 + 4 ln := binary.BigEndian.Uint32(buf[j-4 : j]) if uint64(ln) > math.MaxInt-j { return errors.New("Rat.GobDecode: invalid length") } i := j + int(ln) if len(buf) < i { return errors.New("Rat.GobDecode: buffer too small") } 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 (x *Rat) MarshalText() (text []byte, err error) { if x.IsInt() { return x.a.MarshalText() } return x.marshal(), nil } // UnmarshalText implements the [encoding.TextUnmarshaler] interface. func (z *Rat) UnmarshalText(text []byte) error { // TODO(gri): get rid of the []byte/string conversion if _, ok := z.SetString(string(text)); !ok { return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text) } return nil }