Source file src/pkg/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 (
    10		"bytes"
    11		"fmt"
    12	)
    13	
    14	// Gob codec version. Permits backward-compatible changes to the encoding.
    15	const intGobVersion byte = 1
    16	
    17	// GobEncode implements the gob.GobEncoder interface.
    18	func (x *Int) GobEncode() ([]byte, error) {
    19		if x == nil {
    20			return nil, nil
    21		}
    22		buf := make([]byte, 1+len(x.abs)*_S) // extra byte for version and sign bit
    23		i := x.abs.bytes(buf) - 1            // i >= 0
    24		b := intGobVersion << 1              // make space for sign bit
    25		if x.neg {
    26			b |= 1
    27		}
    28		buf[i] = b
    29		return buf[i:], nil
    30	}
    31	
    32	// GobDecode implements the gob.GobDecoder interface.
    33	func (z *Int) GobDecode(buf []byte) error {
    34		if len(buf) == 0 {
    35			// Other side sent a nil or default value.
    36			*z = Int{}
    37			return nil
    38		}
    39		b := buf[0]
    40		if b>>1 != intGobVersion {
    41			return fmt.Errorf("Int.GobDecode: encoding version %d not supported", b>>1)
    42		}
    43		z.neg = b&1 != 0
    44		z.abs = z.abs.setBytes(buf[1:])
    45		return nil
    46	}
    47	
    48	// MarshalText implements the encoding.TextMarshaler interface.
    49	func (x *Int) MarshalText() (text []byte, err error) {
    50		if x == nil {
    51			return []byte("<nil>"), nil
    52		}
    53		return x.abs.itoa(x.neg, 10), nil
    54	}
    55	
    56	// UnmarshalText implements the encoding.TextUnmarshaler interface.
    57	func (z *Int) UnmarshalText(text []byte) error {
    58		if _, ok := z.setFromScanner(bytes.NewReader(text), 0); !ok {
    59			return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
    60		}
    61		return nil
    62	}
    63	
    64	// The JSON marshalers are only here for API backward compatibility
    65	// (programs that explicitly look for these two methods). JSON works
    66	// fine with the TextMarshaler only.
    67	
    68	// MarshalJSON implements the json.Marshaler interface.
    69	func (x *Int) MarshalJSON() ([]byte, error) {
    70		return x.MarshalText()
    71	}
    72	
    73	// UnmarshalJSON implements the json.Unmarshaler interface.
    74	func (z *Int) UnmarshalJSON(text []byte) error {
    75		// Ignore null, like in the main JSON package.
    76		if string(text) == "null" {
    77			return nil
    78		}
    79		return z.UnmarshalText(text)
    80	}
    81	

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