Source file src/pkg/math/big/ratmarsh.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 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		b := buf[0]
    49		if b>>1 != ratGobVersion {
    50			return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
    51		}
    52		const j = 1 + 4
    53		i := j + binary.BigEndian.Uint32(buf[j-4:j])
    54		z.a.neg = b&1 != 0
    55		z.a.abs = z.a.abs.setBytes(buf[j:i])
    56		z.b.abs = z.b.abs.setBytes(buf[i:])
    57		return nil
    58	}
    59	
    60	// MarshalText implements the encoding.TextMarshaler interface.
    61	func (x *Rat) MarshalText() (text []byte, err error) {
    62		if x.IsInt() {
    63			return x.a.MarshalText()
    64		}
    65		return x.marshal(), nil
    66	}
    67	
    68	// UnmarshalText implements the encoding.TextUnmarshaler interface.
    69	func (z *Rat) UnmarshalText(text []byte) error {
    70		// TODO(gri): get rid of the []byte/string conversion
    71		if _, ok := z.SetString(string(text)); !ok {
    72			return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
    73		}
    74		return nil
    75	}
    76	

View as plain text