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Source file src/math/big/intmarsh.go

     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 Ints.
     6	
     7	package big
     8	
     9	import "fmt"
    10	
    11	// Gob codec version. Permits backward-compatible changes to the encoding.
    12	const intGobVersion byte = 1
    13	
    14	// GobEncode implements the gob.GobEncoder interface.
    15	func (x *Int) GobEncode() ([]byte, error) {
    16		if x == nil {
    17			return nil, nil
    18		}
    19		buf := make([]byte, 1+len(x.abs)*_S) // extra byte for version and sign bit
    20		i := x.abs.bytes(buf) - 1            // i >= 0
    21		b := intGobVersion << 1              // make space for sign bit
    22		if x.neg {
    23			b |= 1
    24		}
    25		buf[i] = b
    26		return buf[i:], nil
    27	}
    28	
    29	// GobDecode implements the gob.GobDecoder interface.
    30	func (z *Int) GobDecode(buf []byte) error {
    31		if len(buf) == 0 {
    32			// Other side sent a nil or default value.
    33			*z = Int{}
    34			return nil
    35		}
    36		b := buf[0]
    37		if b>>1 != intGobVersion {
    38			return fmt.Errorf("Int.GobDecode: encoding version %d not supported", b>>1)
    39		}
    40		z.neg = b&1 != 0
    41		z.abs = z.abs.setBytes(buf[1:])
    42		return nil
    43	}
    44	
    45	// MarshalText implements the encoding.TextMarshaler interface.
    46	func (x *Int) MarshalText() (text []byte, err error) {
    47		if x == nil {
    48			return []byte("<nil>"), nil
    49		}
    50		return x.abs.itoa(x.neg, 10), nil
    51	}
    52	
    53	// UnmarshalText implements the encoding.TextUnmarshaler interface.
    54	func (z *Int) UnmarshalText(text []byte) error {
    55		// TODO(gri): get rid of the []byte/string conversion
    56		if _, ok := z.SetString(string(text), 0); !ok {
    57			return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
    58		}
    59		return nil
    60	}
    61	
    62	// The JSON marshalers are only here for API backward compatibility
    63	// (programs that explicitly look for these two methods). JSON works
    64	// fine with the TextMarshaler only.
    65	
    66	// MarshalJSON implements the json.Marshaler interface.
    67	func (x *Int) MarshalJSON() ([]byte, error) {
    68		return x.MarshalText()
    69	}
    70	
    71	// UnmarshalJSON implements the json.Unmarshaler interface.
    72	func (z *Int) UnmarshalJSON(text []byte) error {
    73		// Ignore null, like in the main JSON package.
    74		if string(text) == "null" {
    75			return nil
    76		}
    77		return z.UnmarshalText(text)
    78	}
    79	

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