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Source file src/math/big/intmarsh.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 Ints.
  
  package big
  
  import "fmt"
  
  // Gob codec version. Permits backward-compatible changes to the encoding.
  const intGobVersion byte = 1
  
  // GobEncode implements the gob.GobEncoder interface.
  func (x *Int) GobEncode() ([]byte, error) {
  	if x == nil {
  		return nil, nil
  	}
  	buf := make([]byte, 1+len(x.abs)*_S) // extra byte for version and sign bit
  	i := x.abs.bytes(buf) - 1            // i >= 0
  	b := intGobVersion << 1              // make space for sign bit
  	if x.neg {
  		b |= 1
  	}
  	buf[i] = b
  	return buf[i:], nil
  }
  
  // GobDecode implements the gob.GobDecoder interface.
  func (z *Int) GobDecode(buf []byte) error {
  	if len(buf) == 0 {
  		// Other side sent a nil or default value.
  		*z = Int{}
  		return nil
  	}
  	b := buf[0]
  	if b>>1 != intGobVersion {
  		return fmt.Errorf("Int.GobDecode: encoding version %d not supported", b>>1)
  	}
  	z.neg = b&1 != 0
  	z.abs = z.abs.setBytes(buf[1:])
  	return nil
  }
  
  // MarshalText implements the encoding.TextMarshaler interface.
  func (x *Int) MarshalText() (text []byte, err error) {
  	if x == nil {
  		return []byte("<nil>"), nil
  	}
  	return x.abs.itoa(x.neg, 10), nil
  }
  
  // UnmarshalText implements the encoding.TextUnmarshaler interface.
  func (z *Int) UnmarshalText(text []byte) error {
  	// TODO(gri): get rid of the []byte/string conversion
  	if _, ok := z.SetString(string(text), 0); !ok {
  		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
  	}
  	return nil
  }
  
  // The JSON marshalers are only here for API backward compatibility
  // (programs that explicitly look for these two methods). JSON works
  // fine with the TextMarshaler only.
  
  // MarshalJSON implements the json.Marshaler interface.
  func (x *Int) MarshalJSON() ([]byte, error) {
  	return x.MarshalText()
  }
  
  // UnmarshalJSON implements the json.Unmarshaler interface.
  func (z *Int) UnmarshalJSON(text []byte) error {
  	// Ignore null, like in the main JSON package.
  	if string(text) == "null" {
  		return nil
  	}
  	return z.UnmarshalText(text)
  }
  

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