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Source file src/math/big/ratmarsh.go

  // 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 (x *Rat) MarshalText() (text []byte, err error) {
  	// TODO(gri): get rid of the []byte/string conversion
  	return []byte(x.RatString()), 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
  }
  

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