ratmarsh.go

Documentation: math/big

		 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  
		 7  package big
		 8  
		 9  import (
		10  	"encoding/binary"
		11  	"errors"
		12  	"fmt"
		13  )
		14  
		15  // Gob codec version. Permits backward-compatible changes to the encoding.
		16  const ratGobVersion byte = 1
		17  
		18  // GobEncode implements the gob.GobEncoder interface.
		19  func (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.
		42  func (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  	if len(buf) < 5 {
		49  		return errors.New("Rat.GobDecode: buffer too small")
		50  	}
		51  	b := buf[0]
		52  	if b>>1 != ratGobVersion {
		53  		return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
		54  	}
		55  	const j = 1 + 4
		56  	i := j + binary.BigEndian.Uint32(buf[j-4:j])
		57  	if len(buf) < int(i) {
		58  		return errors.New("Rat.GobDecode: buffer too small")
		59  	}
		60  	z.a.neg = b&1 != 0
		61  	z.a.abs = z.a.abs.setBytes(buf[j:i])
		62  	z.b.abs = z.b.abs.setBytes(buf[i:])
		63  	return nil
		64  }
		65  
		66  // MarshalText implements the encoding.TextMarshaler interface.
		67  func (x *Rat) MarshalText() (text []byte, err error) {
		68  	if x.IsInt() {
		69  		return x.a.MarshalText()
		70  	}
		71  	return x.marshal(), nil
		72  }
		73  
		74  // UnmarshalText implements the encoding.TextUnmarshaler interface.
		75  func (z *Rat) UnmarshalText(text []byte) error {
		76  	// TODO(gri): get rid of the []byte/string conversion
		77  	if _, ok := z.SetString(string(text)); !ok {
		78  		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
		79  	}
		80  	return nil
		81  }
		82
View as plain text